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67. THE COLOURS OF ANIMALS: Their Meaning and Use. By EDWABD 







THE figures have been copied, by kind permission of the author, and 
the council of the Linnean Society, from the plates accompany- 
ing Mr. Koland Trimen's paper, ' On some Remarkable Mimetic 
Analogies among African Butterflies.' ('Linn. Soc. Trans.' vol. 
xxvi. pp. 497, et seqq.) 

All figures are represented one-half of their natural size. The 
appearance of the under side of the wings is shown on the left hand 
of the four upper figures. 

Figure 1. The male of Papilio merope (now called P. cenea ; the 
name P. merope being restricted to the West African form), from 
Knysna, Cape Colony. A closely allied butterfly (P. meriones), 
with a very similar male, is found in Madagascar. 
Figure 2. The female of Papilio meriones, from Madagascar. The 
male is almost exactly like Figure 1. The black bar on the costal 
margin of the fore wing of the female probably represents the 
beginning of the darkening which has been carried so far in the 
females of the African P. merope and P. cenea. 
Figure 3. First or cenea-torm of female of Papilio merope (now 
called P. cenea), from Knysna, Cape Colony. The female is totally 
unlike the male of the same species (Figure 1), but closely mimics 
an unpalatable butterfly, Danais echeria, prevalent in its locality. 
The appearance of the latter is shown in Figure Ba. The mimetic 
resemblance is seen to be very striking on both upper and under 
sides of the wings. A local variety of the Danais is also 
mimicked by a corresponding variety of the Papilio. 
Figure 4. Second or hippocoon-form of female of Papilio merope 
(now called P. cenea), from Graham's Town, Cape Colony. This 
variety mimics the southern form of the unpalatable Danais 
niavius, shown in Figure 4a. 

Figure 5. --Third or tropJionius-tona. of female of Papilio merope 
(now called P. cenea), from Knysna, Cape Colony. This variety 
mimics the abundant and unpalatable Danais chrysippus shown 
in Figure 5a. 

In a closely allied species of Papilio from West Africa (the true 
Papilio merope) the male closely resembles Figure 1, while there are 
two mimetic varieties of female. The hippocoon-iorm is like Figure 4, 
except that it is larger and the white patch on the hind wing 
is smaller ; corresponding in both these respects to the West African 
variety of Danais niavius. The trophonitis-torm resembles Figure 5. 
There is no cenea-torm of this species. For further details see 
pp. 234-38. 













I HAVE adopted a general title, 'The Colours of 
Animals,' in order to indicate the contents of this 
volume, although the vast majority of the examples 
are taken from insects, and indeed almost invariably 
from a single order, the Lepidoptera. The examples 
are, however, employed merely to illustrate principles 
which are of wide appli cation. 

I have purposely abstained from multiplying in- 
stances when a little observation or even reflection 
will supply them in large numbers. For example, 
the ordinary Protective Resemblances of mammals 
and birds are barely alluded to, on this account. On 
the other hand, more difficult problems, such as the 
change of colour in arctic mammals, or the meaning 
of the colours of birds' eggs, are treated at far greater 
length. My object in both cases is the same : to 
stimulate observation in a subject which will amply 
repay investigation, from the scientific value of the 
results, and the never-failing interest and charm of 
the inquiry. 


Variable Protective Eesemblance in insects is 
treated in considerable detail, for the reasons given 
above, and because much of the work is so recent 
that no complete account can be found outside the 
original memoirs. 

My chief object has been to demonstrate the 
utility of colour and marking in animals. In many 
cases I have attempted to prove that Natural Selection 
has sufficed to accouDt for the results achieved ; and 
I fully believe that further knowledge will prove that 
this principle explains the origin of all appearances 
except those which are due to the subordinate prin- 
ciple of Sexual Selection, and a few comparatively 
unimportant instances which are due to Isolation or 
to Correlation of Growth. 

In support of these views I have endeavoured to 
bring together a large amount of experimental evi- 
dence in favour of the theories as to the various uses of 
colour. 'Further experiments are still greatly needed. 

In the chapters on ' Sexual Selection ' I have 
argued in favour of Darwin's views, and have 
attempted to defend them against recently published 

At the conclusion of the volume I have brought 
forward a detailed classification of the various uses 
of colour, in which new, and, I believe, more con- 
venient terms are suggested. Definitions and exam- 
ples are also given in the classification, which is, in 
fact, a brief abstract of the whole book. 


I have to thank the Councils of various scientific 
societies for the courteous permission to copy figures 
from their respective publications. The figures in 
the coloured plate are copied from the plates accom- 
panying Mr. Eoland Trimen's paper in the ' Trans- 
actions of the Linnean Society,' vol. xxvi. pp. 
497-522. Figures 18, 19, 20, 21, and 22 are copied 
from the plate accompanying Mr. E. Bowdler Sharpe's 
paper in the ' Proceedings of the Zoological Society,' 
1873, pp. 414 et seqq. Figures 3, 4, 5, 6, 7, 8, 11, 
14, 58, 60, 61, 62 are copied from the plates and 
woodcuts accompanying my papers in the ' Transac- 
tions of the Entomological Society,' 1884, 1885, 1887, 
and 1888. Figures 25, 26, and 27 are copied from 
the plate accompanying Mrs. Barber's paper in the 
' Transactions of the Entomological Society,' 1874, 
pp. 519 et seqq. Figures 29 and 30 are copied from 
the plate and woodcuts accompanying my paper in 
the ' Philosophical Transactions of the Eoyal Society,' 
vol. 178 (1887), B, pp. 311-441. Figures 15, 16, 53, 
54, 63, 64, 65, 66 are copied from the woodcuts and 
plates accompanying G. W. and E. G. Peckham's 
paper in the ' Occasional Papers of the Natural 
History Society of Wisconsin,' vol. i. (1889), Milwaukee. 
Figures 55 and 56 are copied from the plates accom- 
panying Professor Weismann's ' Studies in the Theory 
of Descent,' translated by Professor Meldola. Figure 
10 is copied from one of the plates accompanying Dr. 
Wilhelm Midler's ' Siidamerikanische Nymphaliden- 


raupen' (' Zoologische Jahrbiicher,' J. W. Spengel, 
Jena, 1886). Figure 42 is copied from Vogt (' The 
Natural History of Animals ' : English translation : 
Blackie and Son). Figures 44 and 45 are copied 
from the plates accompanying Curtis's 'British 
Lepidoptera.' The remaining figures are original. 
Figure 17 was kindly lent me by Dr. A. K. Wallace, 
to whom it had been sent by Mr. Wood-Mason. In 
preparing the drawings of the original figures I have 
been greatly assisted by my wife, my sister Miss L. S. 
Poulton, Miss Herman Fisher, Mr. Alfred Sich, 
Mr. Alfred Robinson, and especially by Miss Cundell. 
I have almost invariably referred to original 
papers from which facts or conclusions have been 
adopted; so that any reader having access to a 
scientific library may easily gain possession of further 
details. Not wishing to overburden the book with 
such notes, I have abstained from referring constantly 
to my own papers, although most of the examples are 
taken from them. A list of my papers which deal 
with the colours of insects is therefore printed below. 

Transactions Entomological Society,' London, 1884, pp. 27-60 

1885, 281-329 

1886, 137-179 

1887, 281-321 

* .. >. 1888, 515-606 

Philos. Trans. Royal Society,' vol. 178 (1887), B, pp. 311-441 
Abstract of the above in 'Proceedings Royal Society,' 1887, vol. xlii. 

pp. 94-108 
' Proceedings Royal Society,' 1885, vol. xxxviii. pp. 269-315 

1886, vol. xl. pp. 135-173 
' Proceedings Zoological Society,' 1887, pp. 191-274 


Short papers or notes (exclusive of those which 
are mere abstracts of the above) : 

' Proceedings Entomological Society,' London, 1887, pp. 1-li 

1887, Ixi-lxii 
1888, p. v 

> > > > PP- viii x 


1889 xxxvii-xl 
' Journal of the Victoria Institute,' 1888, vol. xxii., ' On Mimicry.' 

It is my pleasant duty to thank many friends for 
their kind assistance. I owe to Professor Meldola 
more than I can possibly express : his writings first 
induced me to enter upon this line of investigation, 
and I have had the benefit of his great experience 
and wise advice during the whole of the time that I 
have been at work. Nearly every subject touched 
upon in this volume has been discussed with him. 

Professor Westwood has always been most kind 
in helping me with the literature of the subject, with 
which he has so intimate an acquaintance, and in 
giving me the free use of the Hope collection at 
Oxford. Professor E. Eay Lankester has read the 
proof-sheets dealing with the classifications of the 
uses of colour, and has offered valuable suggestions. 
Several beautiful examples were suggested to me by 
Professor C. Stewart. Dr. Giinther, Mr. Eoland 
Trimen, Mr. Oldfield Thomas, Mr. E. Bowdler Sharpe, 
Mr. F. E. Beddard, Mr. W. W. Fowler, and Mr. A. 
H. Cocks have been very kind in answering questions 
upon their special subjects. Sir John Conroy has 


kindly helped me in explaining the physical questions 
involved in the first chapter. I am especially pleased 
to speak of the help received from my former pupils 
Mr. W. Garstangand Mr. E. C. L. Perkins, who have 
supplied many valuable instances, which are specified 
in the volume, where other kind assistance is also duly 

Although I have ventured to disagree with my 
friend Dr. A. R. Wallace upon the subject of ' Sexual 
Selection,' I wish to acknowledge how very much I 
owe to his writings, which I have very frequently 
quoted. I have also made great use of the late 
Thomas Belt's extremely interesting and suggestive 
' Naturalist in Nicaragua.' 

Among recent papers I wish especially to mention 
that by G. W. and E. G. Peckham, of Milwaukee, 
U.S.A. The minute observation of these authors 
upon the courtship of spiders of the family Attidce is 
a model for investigation in a subject which has never 
before been attacked systematically. 

Above all, I should wish to acknowledge, although 
I can never fully express, the depth of my indebted- 
ness to the principles which first made Biology a 
science, the principles enunciated by Charles Darwin. 
It is common enough nowadays to hear of new 
hypotheses which are believed (by their inventors) to 
explain the fact of evolution. These hypotheses are 
as destructive of one another as they are supposed to 
be of Natural Selection, which remains as the one 


solid foundation upon which evolution rests. I have 
wished to express this conviction because my name 
has been used as part of the support for an opposite 
opinion, by an anonymous writer in the ' Edinburgh 
Eeview.' 1 In an article in which unfairness is as 
conspicuous as the prejudice to which it is due, I am 
classed as one of those ' industrious young observers ' 
who ' are accumulating facts telling with more or less 
force against pure Darwinism.' 2 On the strength of 
this and other almost equally strange evidence, the 
Eeviewer triumphantly exclaims, ' Darwin, the thanes 
fly from thee ! ' In view of this public mention of my 
name, I may perhaps be excused for making the per- 
sonal statement that any scientific work which I have 
had the opportunity of doing has been inspired by 
one firm purpose the desire to support, in however 
small a degree, and to illustrate by new examples, 
those great principles which we owe to the life and 
writings of Charles Darwin, and especially the pre- 
eminent principle of Natural Selection. 

E. B. P. 
OXFORD : Dec. 28, 1889. 

1 Edinburgh Review. Article V. April 1888, pp. 407-47. 

* p. 443. The bias of the writer appears in a most singular 
manner upon this page. In the short space of seventeen lines the 
following adjectives are divided between five writers and their works 
industrious, illustrious, gifted, well-read, acute, intelligent, brilliant, 
thoughtful. I need hardly say that all five writers are believed by 
the Reviewer to oppose the theory of Natural Selection. 










ETC 81 

tinued) 133 


XI. WARNING COLOURS (continued) 189 









Colours due to absorption 

THE colours of animals are produced in various ways. 
By far the commonest method is the absorption of 
certain elements of light by means of special sub- 
stances which are called pigments, or colouring matters. 
The colour of each pigment is due to those elements 
of the light which it does not absorb, and which can 
therefore emerge and affect the eye of the spectator. 
Black is, of course, caused by the absorption of all 
the constituents of light, so that nothing reaches the 
eye. The colour of red pigment, like that of red 
glass, depends upon the fact that red is less absorbed 
than any other element of the light which passes 
through. If a sheet of red glass be placed upon 
white paper, the light traverses the glass, is reflected 


from the surface of the paper, re-traverses the glass, 
and emerges. Similarly, in painting, bright effects 
are produced by covering a surface of Chinese white 
with the desired colour. The light passing twice 
through the thickness of the colour, absorption is 
far more complete than when only one thickness is 
traversed, as in a piece of red glass held up to the 
light. Absorption being more complete, the red colour 
is deeper. Animal pigments are nearly always twice 
traversed by the light, and therefore a very thin layer 
produces a considerable effect. 

Animal colours are therefore generally due to 
precisely the same optical principle which causes the 
colour of a wall-paper, a carpet, or a picture. Certain 
transparent animals are, however, for the most part 
coloured by light which passes but once through them, 
upon the same principle as the colours of a stained- 
glass window. The beautiful transparent blue of 
many pelagic animals, such as the Portuguese Man- 
of-war (Physalia), is caused in this way. 

It would be out of place to discuss the details of 
the causes of colour by absorption. I may, however, 
mention that vibrations of very different rates are 
started in the luminiferous ether by the sun, the 
electric light, &c. A certain series of these vibrations 
causes the effect of white light when it falls on our 
retina; but there are vibrations above and below 
this visible series vibrations which we cannot see. 
We can, however, prove their existence in other ways ; 


and it is certain that some animals can see vibrations 
which do not affect our eyes. 1 The slowest vibrations 
that we can see, produce the effect of red, the most 
rapid the effect of violet, while the intermediate 
vibrations cause the other well-known colours of the 
rainbow or the spectrum. 

The absorption of certain elements of light there- 
fore means the disappearance of ethereal vibrations 
with a certain speed. It is believed that these 
vibrations disappear because their motion has been 
communicated to the particles of the absorbing body. 
It is also believed that these particles are in a state of 
constant vibration, and that the vibrations of ether, 
which are timed to those of the body, are used up 
in increasing the motion of the latter. 

A white appearance due to light being scattered 

The production of white is due to a different 
principle, for we know that when light passes through 
a body without any absorption, the body is trans- 
parent and invisible rather than white. When all 
the light passes through, the body is completely in- 
visible. Whiteness is due to reflection of the whole 
visible series of vibrations, unaccompanied by the 
absorption of a part of them, as in the production of 
colours. But regular reflection, viz. reflection from 

1 Sir John Lubbock, The Senses of Animals, Chapter X. (Inter- 
national Scientific Series). 


a polished surface like that of a mirror, does not 
cause whiteness : it renders the surface itself invisible, 
but produces images of surrounding objects. A white 
appearance is produced by irregular reflection, which 
causes the light to be scattered or reflected in all 
directions. To produce such a result there must 
be an immense number of surfaces in an immense 
number of different directions. If a coloured sub- 
stance be reduced to powder of various degrees of 
fineness, the colour will diminish in intensity, and 
the whiteness will increase, according to the fineness 
of the powder ; this is because the number of re- 
flecting surfaces is increased, while the thickness of 
the grains is diminished. This will be clear from the 
following consideration. When a beam of light falls on 
a sheet of glass, a known fraction (about 4 per cent.) 
of the light is reflected back from the first surface : the 
larger portion, however, enters the glass, and, after 
suffering a certain amount of absorption, reaches the 
second surface and is again partially reflected. If the 
glass be powdered, the number of surfaces will be so im- 
mensely increased that all the light will be reflected 
by a small thickness of the powder. The light 
reflected from the second surface of each grain of 
coloured glass will still be coloured by absorption, but 
not sufficiently to produce any visible results, when 
the thickness of the grain is very small. 

Reflection is the immediate cause of whiteness, and 
the amount of reflection is due to the difference 


between the refractive powers (viz. the power of 
changing the direction of rays of light) possessed by 
the grains of glass and the substance, such as air or 
water, which lies between them. Thus the refractive 
powers of glass and water are much nearer than 
those of glass and air : hence a dry powder will 
reflect far more than a wet one, and will appear 
much whiter. 

To take a few familiar examples : snow is white, 
because of the minute globules of air which refract 
very differently from the crystals between which they 
are entangled ; ice, on the other hand, is transparent. 
If snow be compressed the air is driven out, and the 
mass becomes transparent ; if ice be powdered it be- 
comes white like snow. The froth of a coloured liquid 
is not coloured like the latter, but is white. Milk and 
fat are white because light is scattered from the 
surfaces of the countless oil globules, which refract 
very differently from the substance which lies between 
them. The surface of well-polished glass is almost 
invisible, because it reflects regularly, but a scratched 
surface is very visible, because there are surfaces in 
many different directions, which therefore scatter the 
light, while the far more numerous surfaces of ground 
glass scatter the light far more effectually and produce 
a white appearance. 

The white markings of animals are produced in 
various ways. White hairs and feathers owe their 
appearance, like snow, to the number of minute 


bubbles of gas which are contained in their inter- 
stices. Fat is also made use of to give a white 
appearance ; and the same result may be obtained by 
the presence of minute granules, probably akin to 
pigment, but differing widely from it in optical pro- 
perties, in that no absorption takes place. 

Colours due to thin plates 

It has been stated already that when light traverses 
a sheet of glass surrounded by air, a certain pro- 
portion of it is reflected back at the first surface and 
a certain proportion at the second surface. The 
light will be reflected in the same direction from 
both surfaces. It is believed that the vibrations of 
ether, some of which affect us as light, are in the form 
of undulations of different lengths ; if, therefore, the 
sheet of glass be sufficiently thin, some of the undula- 
tions reflected from the second surface will interfere 
with those started from the first surface. This will 
happen when the sheet is of such a thickness that the 
wave of light reflected from the second surface is half 
an undulation behind that reflected from the first 
surface ; for then the two sets of undulations will be in 
opposite directions, and will therefore neutralise each 

This will be quite clear if we apply the same 
reasoning to those visible undulations from which 
the name itself has been borrowed the waves on the 
surface of water. If a set of ripples is started by the 


motion of an object in still water, and then another 
set is started from another object moved, so that the 
ripples succeed each other at exactly the same rate 
as the preceding set, and if the second set is begun 
when the first has advanced half a complete ripple 
(viz. a movement up and down), it is clear that the 
upward movement of the second will correspond to 
the downward movement of the first and vice versa, 
so that, if the objects are so placed that the two sets 
of ripples are traversing the same sheet of water, 
they will neutralise and destroy each other. 

If we compare a number of sheets of glass which 
are successively thinner and thinner, interference will 
first occur among the longest undulations of light, 
because half an undulation will of course require a 
greater distance (or thickness) than when the undula- 
tions are shorter. As thinner and thinner sheets are 
examined interference will gradually pass through 
the whole spectrum from red to violet, destroying 
sets of waves with shorter and shorter undulations. 
The colour seen in each case will be due to the other 
sets of waves which are not destroyed. 

The amount of reflection, and therefore of inter- 
ference and of colour produced, depends upon the 
difference between the refractive power of the thin 
sheet and the substance on each side of it. 

Such interference colours are seen in a soap- 
bubble, and the colours change as the bubble be- 
comes larger and the film thinner : they differ, too, 


on the various parts of the bubble, because the thin- 
ness also varies. A bubble of melted glass may be 
blown thin enough to produce the same effects, which 
are also well seen when a thin layer of air is enclosed 
between two sheets of glass or between the plates of 
some crystals, or when a drop of oil is allowed to 
spread out into a thin film on the surface of water. 
When a substance has a laminated structure, and 
sufficiently thin films are enclosed between the laminae, 
very marked effects are seen. Thus the metallic 
appearance of the laminated flakes which are formed 
on the surface of glass which has been long buried 
in the earth, is accounted for. If these brilliant 
flakes are wetted the colour fades away, because the 
thin films of air between the laminas are displaced by 
water, with a refractive power much nearer to that of 
the glass, and the amount of reflected light is there- 
fore diminished. 

Interference colours due to thin films are certainly 
very important among animals, but the extent to 
which they occur is imperfectly known. The irides- 
cent colours of many beetles' wings are probably due 
to thin films of air included between layers of a horny 
consistence Such colours are unaltered in dried 
specimens. In other cases the chinks between the 
layers are kept open by films of less powerfully re- 
fractive liquids. When the tissue becomes dry the 
films evaporate and the colour disappears. We 
must suppose that the denser layers come together, 


obliterating the chinks and excluding the air; otherwise 
the colours would be more brilliant than ever, because 
the refractive power of air is even lower than that of 
the liquids. The brilliant metallic appearance of 
many chrysalides, especially in the genus Vanessa, 
is caused by a large number of films of liquid enclosed 
between the laminae of the dense outer layer. If the 
pupa be kept in spirit or water the colour remains, 
but disappears directly it is dry, although it can be 
renewed any number of times by wetting. This may 
even occur in a living animal, for Dr. Sharp has just 
directed my attention to an interesting observation 
made by Dr. Nickerl, who found that a brilliantly 
golden beetle (Carabus auronitens) lost all its lustre 
after hybernating in captivity, but entirely regained 
it after drinking some water. 

Colours due to diffraction 

When white light falls upon a surface on which 
there are a number of fine parallel grooves the re- 
flected light appears coloured, the colour varying with 
the angle at which the light falls on the surface, and 
with the angle at which it is seen. This is due to the 
light reflected from different portions of the surface 
having different distances to travel before reaching the 
observer : and when (as occurs when the grooves are 
very close together) these differences amount to half 
a complete undulation for any particular length of 
vibration, interference is caused, and the vibration 


of that particular rate is wanting from the reflected 
light, which therefore appears coloured. 

Opinions differ as to the relative importance of 
animal colours due to thin plates and to diffraction. 
Many which were believed to result from the latter 
are in all probability due to the former. The irides- 
cent colours on the inner surface of many shells 
(mother-of-pearl) are at any rate partially caused by 
diffraction, for an accurate cast of the surface exhibits 
traces of the colours. 1 The shell is, however, a 
laminated structure, and the colours may therefore 
in part be caused by thin plates. 

Colours due to refraction (prismatic colours) 

When light passes through a wedge-shaped trans- 
parent substance (or prism) with greater refractive 
power than the surrounding medium, it is bent in the 
same direction at both surfaces, but its different con- 
stituents are bent unequally. The slowest vibrations 
(red) are bent least, the most rapid (violet) most ; and 
when the substance possesses a sufficiently high re- 
fractive power, all the colours of white light are seen 
arranged like the rays of a fan in the order of their 
rates of vibration. Prismatic colours like those of the 
diamond are due to refraction. 

1 Professor C. Stewart informs me that he has repeated Brewster's 
original experiment, upon which the above statement depends. He 
found that the colour was due to a thin layer of shell which had been 
stripped off and adhered to the surface of the wax. 


It is doubtful how far the colours of animals are 
caused by this principle ; but Dr. Gadow has given 
strong reasons for supposing that the metallic 
colours of birds' feathers are produced in this way, 1 
and there are scales on the wings-cases of certain 
beetles (Pachyrhynchus) which also may owe their 
colours to refraction. 

All these causes of animal colours may be conve- 
niently grouped under two heads (1) pigmentary, and 
(2) structural. The first head includes colours caused 
by absorption, and the effects produced vary with the 
chemical nature of the substance (pigment). The 
second head includes the colours or appearances pro- 
duced in all other ways, the efficient cause being the 
structure of the substance rather than its chemical 

1 Proc Zool. Soc. 1882, pp. 409 et ae%. 



I. Non-significant colours 

COLOUR, as such, is not necessarily of any value to an 
organism. Organic substances frequently possess a 
chemical and physical structure which causes certain 
light-waves to be absorbed ; or the elements of tis- 
sues may be so arranged that light is scattered, or 
interference colours are produced. Thus blood is 
red, fat is white, and the external surface of the air- 
bladder in certain fishes has a metallic lustre, like 
silver. In such cases there is no reason why we should 
inquire as to the use or meaning of the colour in the 
animal economy ; the colour, as such, has no more 
meaning than it has in a crystal of sulphate of copper 
or iron. Such colours are the incidental results of 
chemical or physical structure, which is valuable to 
the organism on its own account. This argument 
will be still further enforced if we remember that the 
colours in question are, strictly speaking, not colours 
at all. Blood and fat are so constituted that they 
will be red and white, respectively, in the presence of 


light, but they cannot be said to possess these colours 
in their normal position, buried beneath the opaque 
surface of an animal. 

The existence of non- significant colours is, never- 
theless, most important, for they form the material 
out of which natural or sexual selection can create 
significant colours. Thus, the colour of blood may be 
made use of for ' complexion,' while fat may be em- 
ployed to produce white markings, as in certain insect 
larvae. The yellow, brown, and red fatty matters of 
the connective tissue are accumulated beneath the 
skin in patches, so as to produce patterns. 

All colour originally non-significant 

All animal colour must have been originally non- 
significant, for although selective agencies have found 
manifold uses for colour, this fact can never have 
accounted for its first appearance. It has, however, 
been shown that this first appearance presents no 
difficulty, for colour is always liable to occur as an 
incidental result. This is even true of the various 
substances which seem to be specially set apart for the 
production of colour in animals ; for pigments occur 
abundantly in the internal organs and tissues of many 
forms. The brilliant colours of some of the lower 
organisms are probably also non-significant. In all 
higher animals, however, the colours on the surface 
of the body have been significant for a vast period of 
time, so that their amount, their arrangement in 


patterns, their varying tints, and their relation to the 
different parts of the body, have all been determined 
by natural selection through innumerable generations. 
Because the origin of all pigments is to be found in 
the incidental result of the chemical and physical 
nature of organic compounds, it by no means follows 
that incidental or non-significant colours would have 
appeared at all on the surface of most animals. 
And we find as a matter of fact that such colours 
tend to disappear altogether, directly they cease to be 
useful, as in cave-dwelling animals. On the other 
hand, the non-significant colour of blood or of fat 
would persist undiminished in such forms. 

Colours may be destroyed by natural selection 

Just as natural selection may develop an appear- 
ance which harmonises with the surroundings, out of 
the material provided by non-significant colour, the 
same agency may lead to the disappearance of the 
latter when it impedes the success of an animal hi the 
struggle for existence. Thus the red colour of blood 
has disappeared in certain transparent fishes, which 
are thereby concealed from their enemies. Among the 
manifold possible variations of nature is that of a 
fish with colourless blood, which can, nevertheless, 
efficiently perform all the duties of this fluid. While 
such a variation would be no advantage to the great 
majority of vertebrates, it would be very beneficial to 


a fish which was already difficult to detect on the 
surface of the ocean on account of its transparency. 

II. Significant colours 

Colours may be useful in many ways, and are there- 
fore always liable to be turned to account in one direc- 
tion or another. They may be of direct physiological 
value to the organism, or may assist in the struggle 
for existence by deluding other species, or by aiding 
the individuals of the same species, or they may be 
intimately connected with courtship. 

1. The Direct Physiological Value of colour 

The colour of chlorophyll, which causes the green 
appearance of vegetation, must be intimately con- 
nected with the important changes which take place 
in this substance in the presence of light. It is well 
known that under these circumstances carbon dioxide 
(popularly called ' carbonic acid ') can be split up, 
and its carbon made to unite with the elements of 
water, forming organic substance. Although this 
process has been much studied it is still very imper- 
fectly understood. It is clear, however, that the 
colour of chlorophyll, involving the special absorp- 
tion of certain light-waves, has some direct bearing 
upon the changes which occur. 

No equally clear instance has been proved to occur 
in the animal kingdom, except in those few forms 


which resemble plants in possessing chlorophyll. Dr. 
Hickson, however, believes that among corals ' the most 
widely distributed colours will eventually be proved to 
be allied to chlorophyll . . . and perform a very simi- 
lar if not precisely identical physiological function.' 
It is much to be desired that this interesting sugges- 
tion, which Dr. Hickson supports by many arguments, 
may be thoroughly tested as soon as possible. 1 

In the very common association of coloured sub- 
stances with the important function of respiration, it 
is clear that the colour is not more than incidental ; 
while the fish with transparent blood shows that 
colour is not indispensable for the due performance of 
the function. Pigment is, however, of direct import- 
ance for vision : it is always present in the eyes of 
animals, except in the case of albinos, and it is said 
that even they possess the essential visual pigment 
associated with the termination of the optic nerve 
(retinal purple). 

The difference between the physiological importance 
of colour in animals and plants is well shown by the 
fact that a true albino variety (not merely a varie- 
gated example) of a green plant could not live for any 
length of iime. 

There are, however, certain cases among animals 
in which it is extremely probable that colour is of 
direct physiological value. It is well known that 
dark colours readily absorb radiant heat, while light 

1 A Naturalist in North Cekbes (Hiokson, 1889), pp. 149-51. 


colours do so with difficulty. For this reason black 
clothes are most trying, and white most comfortable, 
in the hottest weather. Conversely, a dark surface 
readily parts with heat by radiation, while a white 
surface retains heat far more effectually. 

A few writers had suggested that these principles 
may explain the colours of certain animals, but the 
question was first fully entered upon in Lord Wal- 
singham's presidential address to the Yorkshire 
Naturalists' Union in 1885. 1 The predominance of 
dark varieties of insects and white varieties of birds 
and mammals in northern latitudes is connected with 
these facts. ' Birds and animals living through the 
winter naturally require to retain in their bodies a 
sufficient amount of heat to enable them to maintain 
their existence, with unreduced vitality, against the 
severities of the climate. Insects, on the contrary, 
require rapidly to take advantage of transient gleams 
of sunshine during the short summer season, and 
may be content to sink into a dormant condition so 
soon as they have secured the reproduction of their 
species ; only to be revived in some instances by a 
return of exceptionally favourable conditions.' 

It would be fatal for the temperature of one of the 
higher vertebrates " to sink a few degrees below the 
normal, except in the case of certain species, such as the 
dormouse, &c., which have the power of hybernating 
in a dormant condition; such animals were once 

1 See Entomological Transactions of the Union for 1885. 


called 'warm-blooded,' but are now more correctly 
termed ' homothermic,' because it is the constancy of 
the temperature which is so important, and which 
must be maintained whether the surrounding medium 
be colder or warmer than themselves. Other animals 
with an inconstant temperature are now correctly 
called ' poikilothermic ' rather than ' cold-blooded.' 

Lord Walsingham's conclusions appear to be sup- 
ported by the fact that young dark-coloured cater- 
pillars, like those of the Emperor Moth (Saturnia 
carpini), or Tortoiseshell Butterfly (Vanessa urticce), 
seek the light side of a glass cylinder, and always 
change their position when the cylinder is turned 
round. The question needs further investigation, 
and much might be learnt by interposing various 
screens between such larvae and the light, thus cutting 
off different sets of light-waves. 

The most important support to the hypothesis is 
found in an experiment made by Lord Walsingham, 
in which several Lepidoptera of different colours were 
placed on a surface of snow exposed to bright sun- 
shine ; in half an hour the snow beneath the darker 
insects showed distinct signs of melting, but no effects 
were seen beneath the others. The differences were 
further brought out in the course of two hours, when 
the darkest insect of the lot, a black Geometer, the 
Chimney-Sweeper (Odezia charophyllata) , ' had de- 
cidedly won the downward race among them.' 

It is therefore certain that the absorption of 


radiant heat is favoured by the dark colours of 
northern insects, and it is in every way probable that 
they are benefited by the warmth received in this way. 
We cannot, however, as yet assert that such dark 
colours are not also advantageous for concealment or 
some other purpose. 

The white appearance of Arctic birds and mam- 
mals must be advantageous for concealment in a region 
so largely covered with snow, but it is very probable 
that advantage is also secured by checking the loss of 
heat through radiation. 

Thus Lord Walsingham's experiments and con- 
clusions seem to prove that colours are sometimes 
of direct physiological value to animals, although a 
great deal more work must be done before we can 
safely estimate the proportion which this advantage 
bears to others also conferred by the same colours 
(see also pages 92-104). 

2. Protective and Aggressive Resemblance 

By far the most widespread use of colour is to 
assist an animal in escaping from its enemies or in 
capturing its prey ; the former is Protective, the latter 
Aggressive. It is probable that these were the first uses 
to which non-significant colours were put. The re- 
semblances are of various kinds ; the commonest cases 
are those of simple concealment. The animal passes 
undetected by resembling some common object which 


is of no interest to its enemies or prey respectively, 
or by harmonising with the general effect of its sur- 
roundings ; the former is Special, the latter General 
Resemblance, and both may be Protective or Aggressive. 
Among the most interesting Special Aggressive Resem- 
blances are the cases of Alluring Colouring, in which the 
animal, or some part of it, resembles an object which 
is attractive to its prey. 

3. Protective and Aggressive Mimicry 

Mimicry is in reality a very important section of 
Special Resemblance. The animal gains advantage by 
a superficial resemblance to some other, and generally 
very different, species which is well known and dreaded 
because of some unpleasant quality, such as a sting or 
an offensive taste or smell, &c., or it may even be pro- 
tected from the animal it resembles : this is Protective 
Mimicry. When, however, the animal resembles another 
so as to be able to injure the latter or some other form 
which accompanies it or is not afraid of it, the Mimicry 
is Aggressive. Although, strictly speaking, Mimicry 
should fall under the last heading, it is so important 
and so different from the other examples of Special 
Resemblance that it is more convenient to consider it 
separately. In the complete classification at the end of 
the book it will be shown in its true position. 


4. Warning colours 

When an animal possesses an unpleasant attribute, 
it is often to its advantage to advertise the fact as 
publicly as possible. In this way it escapes a great 
deal of experimental ' tasting.' The conspicuous 
patterns and strongly contrasted colours which serve 
as the signal of danger or inedibility are known as 
Warning Colours. In other cases such colours or 
markings enable individuals of the same species easily 
to follow those in front to a place of safety, or assist 
them in keeping together when safety depends upon 

It is these Warning Colours which are nearly 
always the objects of Protective Mimicry, and it will 
therefore be convenient to describe the former before 
the latter. 

5. Colours produced by Courtship 

Finally, in the highest animals, the vertebrata and 
many of the most specialised invertebrate groups, we 
have some evidence for the existence of an aesthetic 
sense. Darwin believed that this sense was brought 
into play in courtship, and that colours and patterns 
have been gradually modified by the preference of the 
females for the most beautiful males ; he believed that 
such Sexual Selection accounts for many of the most 
beautiful features possessed by animals, viz. those 
which are especially displayed during courtship. 


Although this hypothesis has been rejected by A. B. 
Wallace, I shall endeavour to support it by some 
striking observations of recent date, and by as far as 
possible answering the objections which have been 
raised, and the hypotheses which have been believed 
to account for the same facts. 

Display in courtship is probably the most recently 
developed of all the various uses of colour among 
animals, and as such, its consideration is best deferred 
until all the others have been described. 

It must not be supposed that the colours of each 
animal will be found to possess but a single use. 
Thus Protective EesemUances are often supplemented 
by Warning Colours or attitudes, which give the 
animal an extra chance of escape after its first line of 
defence has been broken through. It is also the 
general rule for the colours displayed in courtship to 
be hidden beneath protective tints when the animal 
is at rest. 

The colours of animals may be recapitulated as 
follows : 



1. Colours of Direct Physiological Value. 

2. Protective and Aggressive Resemblance. 
8. Protective and Aggressive Mimicry. 

4. Warning Colours. 

6. Colours displayed in Courtship. 


The rest of this volume will be occupied with the 
further consideration of the last four classes of colours. 
It will be remembered that the third class is but a 
special example of the second, which it is convenient 
to treat separately, and to defer until after the fourth 
class has been considered. 




THE first and most important use of colour is to 
enable an animal to conceal itself from its enemies 
or to approach its prey unseen. 1 

Special and General Resemblances 

These results may be achieved in one of two ways : 
either the animal may more or less exactly resemble 
some object which is of no interest to its enemies, or 
it may harmonise with the general artistic effect of 
its surroundings, so that it does not attract attention. 
We may therefore distinguish Special Resemblance, in 
which the appearance of a particular object is copied 
in shape and outline as well as in colour, and General 
Resemblance, in which the general effects of surround- 
ing colours are reproduced. 

In the latter case it is often difficult to believe, 

1 This was thoroughly appreciated by Erasmus Darwin, who 
says : ' The colours of many animals seem adapted to their purposes 
of concealing themselves, either to avoid danger or to spring upon 
their prey.' Zoonomia, 1794, vol. i. p. 509. 


when we look at the animal by itself, that the pro- 
tection is effective and real. We cannot appreciate 
the meaning of the colours of many animals apart 
from their surroundings, because we do not compre- 
hend the complicated artistic effect of the latter. A 
caterpillar in the midst of green leaves may have 
many brilliant tints upon it, and yet may be all the 
better concealed because of their presence ; the ap- 
pearance of the foliage is really less simple than we 
imagine, for changes are wrought by varied lights 
and shadows playing upon colours which are in them- 
selves far from uniform. 

Francis Galton noticed this fact with regard to the 
higher animals in 1851. ' Snakes and lizards are the 
most brilliant of animals ; bat ah 1 these, if viewed at a 
distance, or with an eye whose focus is adjusted, not 
exactly at the animal itself, but to an object more or 
less distant than it, become apparently of one hue 
and lose all their gaudiness. No more conspicuous 
animal can well be conceived, according to common 
idea, than a zebra ; but on a bright starlight night the 
breathing of one may be heard close by you, and yet 
you will be positively unable to see the animal. If 
the black stripes were more numerous he would be 
seen as a black mass ; if the white, as a white one ; 
but their proportion is such as exactly to match the 
pale tint which arid ground possesses when seen by 
moonlight.' l 

1 Galton's South Africa, p. 187 (Minerva Library). 


We shall see that it is common for an insect to be 
protected by Special Resemblance at one time of its 
life, and by General Resemblance at another, or to 
be concealed at different periods of its life by different 
kinds of Special or General Resemblance respectively. 

Each of these forms of Resemblance may be 
Protective or Aggressive according as they are made 
use of to defend from attack or to assist in capture. 
We shall also see that Protective and Aggressive Re 
semblances may be either Constant or Variable ; in 
the latter case, the appearance is capable of adjust- 
ment in order to correspond with changes in the en- 
vironment. This, the highest form of Resemblance, 
will be deferred until the examples of the other form 
have been considered. 

The Larvse of Geometrse as examples of Special 
Protective Resemblance 

There is no better instance of Special Protective 
Resemblance than that afforded by the larvae of 
Geometra, * stick caterpillars ' or ' loopers,' as they 
are often called. These caterpillars are extremely 
common, and between two and three hundred species 
are found in this country ; but the great majority are 
rarely seen because of their perfect resemblance to 
the twigs of the plants upon which they feed. They 
possess only two pairs of claspers, or legs which are 
peculiar to the caterpillar stage, while in nearly all 


other caterpillars there are five pairs. These claspers 
are placed at the hind end of the body, which is 
long, thin, and cylindrical, and stands out like a 
side twig at an acute angle with the stem to which 
the claspers are tightly fixed. The body also often 
possesses little humps which resemble buds or irregu- 
larities of the bark. The caterpillar sits motionless 

FIG. 1. The larva of Swallow-tail Moth 
(Ourapteryx tambucaria) ; last stage ; 
natural size. 

FIG. 2. Twig of currant ; the general 
appearance much like that of fig. 1. 

for hours together, and the only alteration of the 
attitude is brought about by feeding, which generally 
takes place in the evening or at night. The general 
appearance of one of these larvse and its resemblance 
to a twig is shown in figs. 1 and 2, for which I am 
indebted to the kindness of Mr. Alfred Sich. 

The strain on the body during these long periods 



of absolute stillness would be far too great to be 
borne did not the caterpillar spin a thread of silk, 
which is attached at one end to the stem, while the 
other end remains fixed to the head of the animal. 
How great the strain would be without such a support 
may be well understood by any one who has tried to 
hold out the arm straight at right angles to the body 
for five minutes. There is considerable tension upon 
the thread of silk, so that, if it be 
cut, the larva falls back with a jerk, 
making a more obtuse angle with 
the stem ; and it then tries to remain 
rigid in the new position : this is im- 
possible because of the strain, and 
after again falling backwards once or 
twice, and making one or two more 
attempts to keep firm and motionless, 
it is obliged to give up the twig-like 
position while it fixes a new sup- 
porting thread. In some cases the 
caterpillar gains support by holding 
a leaf or twig with one of its three 
pairs of true legs, or legs which will persist in the 
perfect insect (see fig. 3 ; also figs. 40 and 41, page 152). 
These pairs of legs are placed one on each of the 
body-rings behind the head. 

It is very interesting to notice how the head of 
these caterpillars is modified from the usual shape 
into one which suggests the end of a twig. It is very 

FIG. 3. The larva of 
Peppered Moth (Am- 
phidasii bttularia) 
last stage; natural 


common for the crown to be deeply notched, thus 
producing two humps which make a very natural end 
to the apparent twig. In the caterpillar of the Small 
Emerald Moth (Hemithea thymiaria) there are two 
additional humps on the body-ring (prothorax) behind 
the head, and the latter is bent forwards and inwards, 
so that the end of the caterpillar is made up of four 
blunt projections, forming perhaps 
the most suggestive of all the resem- 
blances to the end of a twig. 

In the larva of the Early Thorn 
Moth (Selenia illunaria) the head 
and first two body-rings are bent 
backwards at right angles to the rest 
of the body. The supporting thread 
of silk passes between the third pair 
of true legs, which a,re borne by a 
high ridge projecting from the angle. 
The ridge continues the line of the 
body, and is coloured like it, while 
the head and first rings are of a 
different colour. The whole effect is exceedingly un- 
caterpillar-like, and very suggestive of some eccentric 
vegetable growth (see fig. 4). 

In order that the resemblance may be complete, it 
is essential that the caterpillar should appear to grow 
out of the branch in a natural manner. The two 
pairs of claspers assist in producing this effect, for 
they partially encircle the branch, and appear to be 

FIG. 4. The larva of 
Early Thorn Moth 
(Selenia illunaria) ; 
adult ; natural size. 



continuous with it (see fig. 7, page 31). Between the 
two pairs there is necessarily a furrow, where the body 
of the larva lies along the cylindrical branch. This 
furrow, which, if apparent, would greatly interfere with 
the resemblance, is rendered inconspicuous in the fol- 
lowing manner. The under side of the caterpillar is 
somewhat flattened, so that it is in contact with a 
small part of the circumference of the branch, and 
the furrow on each side is partially filled up, at any 

rate in certain species, by a number of fleshy tubercles. 
The shadow which would betray the furrow is also 
neutralised by the light colour of the tubercles. The 
effect will be clear on comparing a, b, and c in fig. 5 : 
a is a section of a branch just below the point where 
a lateral twig comes off ; 6 a diagrammatic section of 
a branch and the caterpillar's body ; c the same with 
the addition of the tubercles, which render the outline 
more like that of a. 

I will illustrate the extraordinary degree of resem- 


blance attained in Geometra, by a description of the 
larva of one of our most abundant species the Brim- 
stone Moth (Rumia cratcegata). The appearance of the 
larva when seated among the twigs of its commonest 
food -plant hawthorn is shown in fig. 6. It will be 
observed that some of the twigs are slightly bent in 
the middle, and that a projection is placed on the 
angle; these appearances are exactly reproduced in 

Fio. 6. The larva of FIG. 7.-The hind part of the larva of Brimstone 

Brimstone Moth (Ru- Moth (Rumia cratoegata), seen from right 

mia craiaegatd) ; last side, showing junction with branch adult 
stage ; natural size. 

the larva. The hind part of the larva is represented 
in fig. 7 (magnified 4-5 diameters), showing the 
claspers and the fleshy projections which occupy the 
furrow between the larva and the stem. 

The harmony of colour is quite as perfect as the 
resemblance of shape. The smaller branches of the 
hawthorn are partially covered by a thin superficial 
layer of a bluish-grey colour (the cuticle), while the 


deeper layers beneath are brown or green, or mixed 
brown and green ; these tints become visible over a 
large part of the surface, owing to the breaking 
away of the thin layer. Hence the colour of the 
branches is brown or green, mottled with grey, and 
not only are these the exact tints of the larva, 
but the way in which the colours are blended is 
precisely similar hi the annual and the plant. The 
marvellous fidelity with which the details are thus 
reproduced, probably implies that the relation between 
the larva and this species of food-plant is extremely 
ancient. It will be shown below that this caterpillar 
can also adjust its colour to that of its individual 
surroundings, so that it would become greenish if it 
passed its life among young green shoots, and brown 
if it lived upon the older twigs. It is altogether one 
of the most perfectly concealed forms in existence. 

When, however, such 'stick caterpillars' are 
young, they do not sit upon the branches, but upon 
the leaves of their food-plant, and the twig-like 
attitude would then be inappropriate, for we do not 
see twigs projecting from leaves. In some cases the 
caterpillars are green (e.g. Ephyra omicronaria) , and 
so possess a general harmony with the colour of the 
surface behind them; but in other cases they are 
brown, and then the attitude is often modified into 
a different form of Special Resemblance. The 
caterpillar twists itself into a very irregular spiral 
(e.g. Ephyra pendularia, &c.), or into an exceedingly 


angular zigzag (e.g. Selenia illunaria; see fig. 8), thus 
resembling a dead and crumpled piece of leaf, or the 
spiral leaf-case made by other insects, or the excre- 
ment of birds or snails. The caterpillar of Selenia 
illunaria has a very similar structure and colouring 
at the times when it resembles such very different 
objects as a twig and the excrement of a bird, the 
whole difference being made by a modification of atti- 
tude alone (compare figs. 4 and 8). I have seen the 
larva of the Brimstone Moth twisted into a spiral, 
resting motionless close to the 
notch which it had eaten out of 
a leaf ; in this position it forcibly 

suggested the appearance of a *. 8 -- Th e you 

Early Thorn ( 

small piece of leaf which had 

been accidentally torn, and had 

turned brown and curled up, remaining attached to 

the uninjured part of the leaf by one end. 

We may well suppose that the acquisition of a 
form and attitude which lend themselves so readily to 
the purposes of concealment, was very advantageous 
to the ancestral Geometra, and enabled them to spread 
over the vegetable world, dividing into an immense 
number of species, and ousting many larvae with less 
perfect methods of concealment. In their widening 
range certain Geometrce have thus come to feed upon 
low-growing plants which are altogether without twigs 
or branches. The attitude is then modified, and sug- 
gests some object which might be expected to occur 



upon the plant. Thus the caterpillar of the Straw 
Belle (Aspilates gilvaria), feeding upon such plants as 
yarrow and plantain, coils up the anterior part of its 
body into a flat spiral, with the head in the centre. 
Hence the attitude and the whitish colour of the larva 
produce a very considerable resemblance to a small 
bleached and empty snail-shell, which 
would be of no interest to any insect- 
eater. If the colour of the caterpillar 
were darker it might be mistaken for 
a living snail, and it is doubtful how far 
such a resemblance would be to its ad- 
vantage, in the case of birds. 

Another larva, that of the Large 
Emerald Moth (Geometra papilionaria), 
feeding upon catkin -bearing trees, birch 
and nut, resembles the catkins rather 
than the twigs (see fig. 9). It is short 
and stout, and the manner in which the 
body-rings succeed each other forcibly 
suggests the overlapping scales of a cat- 
kin. Some of the larva? are green and 
some brown, like catkins of different colours. 

FIG. 9. - The 
larva of Large 
Emerald Moth 
a green va- 
riety ; last 
stage; natural 

Protective Resemblance to bark and lichen in 

Certain caterpillars belonging to other groups are 
concealed by their resemblance to the bark of tolerably 


thick branches. They lie flattened and closely pressed 
against the bark ; while the furrow which would lead 
to their detection is partially filled up, and the 
shadow neutralised, by a row of fleshy protuberances 
in the caterpillars of the Eed and Crimson Under- 
wing Moths (Catocalida ; see figs. 38 and 39, page 
151), and by hairs in the larva of the December Moth 
(Pcecilocampa populi). This interpretation was first 
offered by Meldola, and it is strongly supported by 
the previously mentioned fact that similar protuber- 
ances occur in Geometrce, and are strictly confined to 
the comparatively short line of contact between the 
larva and the branch. The lichens on the bark are 
very commonly resembled rather than the bark itself. 
This is the case with the last-named larva. The 
caterpillar, chrysalis, and moth of the Black Arches 
(Psilura monacha) are beautifully protected in this 
way. The black pupa is fixed in a chink in the bark 
by a few inconspicuous threads ; its dark colour har- 
monises with the shadow in the chink, while the long 
tufts of greyish hair project and exactly resemble the 
appearance of lichen. Both larva and moth are 
coloured so as to resemble common appearances pre- 
sented by lichens, and both habitually rest on lichen- 
covered bark. A lichen-feeding Geometer (Cleora 
lichenaria) is wonderfully protected in the same 
manner ; the larva often twists itself among the 
irregularities of the lichen, so that it is completely 



invisible. The moth is also similarly concealed, and 
rests on tree-trunks. 

A caterpillar which makes its surroundings 
resemble itself 

In all the examples hitherto described, and count- 
less others, the insect is defended by resembling its 
surroundings ; the very interesting caterpillar of 

a South American 
butterfly. (Anaea 
sp. ?), described by 
Wilhelm Muller, 
acts differently and 
makes its surround- 
ings resemble itself. 
It gnaws the leaf in 
such a manner as to 
leave a number of 
rough models of it- 
self attached to the 
mid-rib, and then sits down beside them. The cater- 
pillar is green above and dark beneath, although 
the former colour interrupts the latter at certain 
points and comes into contact with the mid-rib on 
which the insect is resting. The dark colour is not 
distinguishable from the deep shadow behind the 
leaf, and therefore the appearance is that of an 
elongated patch of green connected with the mid- 

FIG. 10. The larva of Anaea sp. t on the mid-rib 
of a leaf on which are many pieces of leaf of 
the general appearance of the larva; third 
stage ; natural size ; after Wilhelm Muller. 


rib by two narrow stalks. The larva, in eating, 
leaves several pieces of leaf attached to the mid-rib by 
one or two stalks, which, therefore, present a very 
similar appearance to that of the larva itself. The 
concealment which is thus effected is sufficiently 
indicated in fig. 10. 

An appearance of leaf-like flatness conveyed by 
arrangement of colour 

Another very interesting example, in which the 
effect of shadow is gained by arrangement of colour, 
is afforded by the chrysalis of the Purple Emperor 
Butterfly (Apatura iris). The large green pupa re- 
sembles a leaf in the most perfect manner, mid-rib 
and oblique veining being represented. I showed a 
small twig of sallow, to which a pupa was suspended, 
to several friends, but it was almost invariably over- 
looked ; even when it was pointed out, the observer 
frequently failed to see any difference between it and 
a sallow leaf. The most extraordinary thing about 
this resemblance is the impression of leaf-like flatness 
conveyed by a chrysalis, which is in reality very far 
from flat. In its thickest part the pupa is 8'5 mm. 
across, and it is in all parts very many times thicker 
than a leaf. The dorsal side of the pupa forms a 
very thin sharp ridge for part of its length, but the 
slope is much more pronounced in other parts and 
along the whole ventral side. But exactly in these 


places, where the obvious thickness would destroy the 
resemblance to a leaf, the whole effect of the round- 
ness is neutralised by increased lightness, so disposed 
as just to compensate for the shadow by which alone 
we judge of the roundness of small objects. The 
degree of whiteness is produced by the relative abun- 
dance of white dots and a fine white marbling of the 
surface, which is everywhere present mingled with the 
green. The effect is, in fact, produced by a process 
exactly analogous to stippling. The degree of lightness 
produced in this way exactly corresponds to the angle 
of the slope, which, of course, determines the depth 
of the shadow. By this beautiful and simple method 
the pupa appears to be as flat as a leaf which is only 
a small fraction of 1 mm. in thickness. 

Although the effect which I have just described 
could not have been surpassed by the efforts of an 
artist, it is precisely the result which can be most 
readily explained by the unaided operation of natural 
selection. The minute white markings are present. 
over the whole surface, and their number and size 
must be subject to continual variation ; in fact, it is 
quite certain that no two individuals are alike in these 
respects. The increased protection afforded by their 
more appropriate distribution in certain individuals 
would clearly lead to the survival of the latter, while 
the same process continued in each generation would 
lead to the elaborate and beautiful form of adaptation 
which is now witnessed in this species. 


An analogous effect is produced by the larva of a 
Saw-fly (a plant-eating Hymenopterous insect), which 
rests stretched along the edge of a leaf. In this posi- 
tion the larva (Nematus curtispina) would be detected 
if it covered the notched edge of the leaf ; it has, how- 
ever, the habit of resting along the curved edge of the 
gap made by its own exertions. From the side its 
green ground colour is alone apparent, and it is very 
difficult to detect. When, however, the leaf is looked 
at edgeways, it would seem that the larva must be con- 
spicuous, because its thickness is much greater than 
that of a leaf. From this point of view the back of 
the larva is, of course, seen; along 
the middle line the tubular heart is 

more distinct than usual because of FIG. 11. The larva of 

Nematus curtispina ; 

the transparent skin. The green must stage ; natural 
blood within makes the heart appear 
as a fine dark line against a white border on each 
side, which is entirely due to an accumulation of fat 
beneath the skin. The white band with the fine dark 
line down its middle produces the effect of the edge of 
the leaf, while the rest of the body on each side is 
green, shaded with dark pigment so as to appear much 
flatter than it really is. The appearance of the larva 
is shown in fig. 11. 

The case is also of special interest, because the 
colouring is chiefly derived from internal tissues or 
organs showing through a transparent skin. The 
ground colour is due to the green fluids of the body 


and the green contents of the alimentary canal. The 
dark shading is the only part of the appearance caused 
in the usual way by superficially placed pigment. 
Nearly all the colours of this animal are non- 
significant in many other insects. 

Eeply to objection that methods of concealment 
would certainly be detected 

It has been sometimes objected that these methods 
of concealment cannot be intended as a means of 
defence, because insect-eating animals would be 
sharp-sighted enough to penetrate the disguise. Of 
course, the progressive improvement in the means 
of concealment has been attended by a corresponding 
increase in the keenness of foes, so that no species 
can wholly escape. But so long as a well-concealed 
form remains motionless, it is easy to prove by 
experiment that enemies are often unable to recog- 
nise it. Thus I have found that the insect-eating, 
wood-haunting Green Lizard (Lacerta viridis) will 
generally fail to detect a ' stick caterpillar ' in its 
position of rest, although it is seized and greedily 
devoured directly it moves. The marvellous resem- 
blance of Cleora lichenaria (see p. 35) even deceived 
one of these lizards after the larva had moved more 
than once. The instant the caterpillar became rigid 
the lizard appeared puzzled, and seemed unable to 
realise that the apparent piece of lichen was good to 


eat. After a few moments, however, the lizard was 
satisfied, and ate the caterpillar with the keenest 

Furthermore, the fact that all well-concealed 
forms are good for food, and are eagerly chased and 
devoured by insectivorous animals, while unpalatable 
forms are conspicuously coloured, points strongly 
towards the conclusion that the object of concealment 
is defence from enemies. 



(continued), DIMORPHISM, ETC. 

General Protective Resemblance and changes of colour 
corresponding to changes in the surroundings 

ALL the examples hitherto described illustrate Special 
Protective Resemblance. A good instance of General 
Resemblance is afforded by the large and common 
caterpillar of the Privet Hawk Moth (Sphinx ligustri). 
Although the caterpillar looks so conspicuous, it 
harmonises very well with its food-plant, and is some- 
times difficult to find. The purple stripes increase 
the protection by breaking up the large green surface 
of the caterpillar into smaller areas. This cater- 
pillar also affords a good example of a rapid change of 
colour corresponding to a change of environment. 
When full grown it descends to the ground and 
hurries about in search of a spot to bury in, and, 
being very large and bright green, it would be ex- 
ceedingly conspicuous against the brown earth if it 
retained the usual colour. But just before it descends 
the back begins to turn brown, and becomes finally 


dark brown, so that the caterpillar harmonises well 
with the colour of its new surroundings. The sig- 
nificance of this change was first pointed out by 
Professor Meldola. Other nearly allied caterpillars 
feeding upon trees, such as willow or poplar, which 
grow in damp situations where the ground is covered 
with green vegetation, do not turn brown to anything 
like the same extent. 

A very interesting instance of exactly the opposite 
change at a corresponding period is afforded by the 
caterpillar of the August Thorn Moth (Ennomos angu- 
larid), a brown ' stick caterpillar,' protected by a very 
perfect Special Eesemblance to the dark twigs of the 
elm on which it feeds. When full-fed it constructs a 
very loose cocoon of elm leaves, so loose and open that 
it is easily seen within, and its brown body would be 
conspicuous against the background of green leaves. 
But at the same time the dark brown colour of its 
surface entirely disappears, and the animal is tinted 
by its green blood, which is seen through the trans- 
parent skin ; it is thus well concealed by General 
Resemblance to its new surroundings. 

Another exceedingly interesting case of the same 
kind of change is witnessed in the caterpillar of the 
Miller Moth (Acronycta leporina), which sits motionless 
on the under side of the leaves of the birch and alder, 
and is covered with very long beautiful hair which is 
brilliantly white, and bends over on all sides so as to 
touch the leaf, forming a wide margin round the 


caterpillar. Hence all we can see is an oval convex 
mass of a substance resembling white cotton wool, an 
appearance very suggestive of a cocoon (see fig. 12). 
The caterpillar's body is almost invisible ; but on 
looking carefully we can just make out a dim curved 
shape beneath the white covering, just as a caterpillar 
or chrysalis appears through the walls of its cocoon : 

PIG. 12. -The larva of Miller Moth (Aero- FIG. 13. -Thelarva of Miller Moth (Aero- 
nyctaleporina), at rest on a birch leaf ; nycta leporina), wandering about on 

adult ; natural size. bark before forming cocoon ; natural 


furthermore, the larva is very short and thick, and thus 
resembles the contracted state of a caterpillar before 
turning to a chrysalis. This perfect Special Eesem- 
blance is kept up until the caterpillar is full-fed, 
when it wanders over the bark and finally burrows 
in it. But a cocoon is a motionless object, and 
the resemblance, if continued, would be fatal, for it 
would attract attention. But as soon as the larva 


is mature, the hairs become black and the body of a 
much darker tint, and the animal is then well pro- 
tected by General Eesemblance to the dark surface 
over which it moves (see fig. 13). 

Although the bark of large birch trees is chiefly 
white, the caterpillar is, upon the whole, better con- 
cealed by becoming dark-coloured. It lives on small 
birches and alders with dark bark, as well as on 
large birches, and in the latter case it probably 
wanders among the wide dark chinks rather than 
over the smooth wide expanses, for it would certainly 
burrow in the former rather than the latter. 

Just before pupation the colours of caterpillars 
nearly always become dull, and it is in every way 
probable that such incidental changes have been 
seized upon by natural selection, and have been ren- 
dered advantageous to the species. Such alterations 
of colour are entirely different from those which will 
be described below, in which an animal can modify its 
appearance into correspondence with its individual 
surroundings. The larva of the Privet Hawk Moth 
almost invariably wanders over the earth when it 
has come down from its food-plant ; but if it were to 
descend upon turf, the brown colour would still be 
assumed, although green would conceal it more effec- 
tually. The change to brown is, however, far safer 
for the average caterpillar, and is beneficial to the 
species on the whole, although it must lead to some in- 
dividual failures. In the far higher form of Variable 


Protective Resemblance, which will be described in 
Chapters VII., VIII., and IX., the individual can 
adjust its appearance to any of the various environ- 
ments it is h'kely to meet with in nature. 

The consideration of changes in colour very 
naturally leads to the subject of Dimorphism. 

Dimorphism in Lepidopterous larvae 

It has been already mentioned that the caterpillars 
of the Large Emerald Moth are sometimes green and 
sometimes brown. The same is true of many larvae, 
and in some of the Mocha Moths (Ephyrida) the 
chrysalides are the same colour as the larvae from which 
they develop. These colours have nothing to do with 
sex, and the appearance of the perfect insect does not 
seem to be influenced in any way by the larval dimor- 
phism. It is noteworthy that both colours of dimorphic 
larvae are invariably of protective value : they are, in 
fact, nearly always the two chief tints of nature 
green and brown. 

If we breed from moths developed from the green 
larvae of, e.g., the Large Emerald, the larvae in the 
next generation are chiefly green, and after several 
generations there is little doubt that the brown form 
would become excessively rare ; so also the green form 
would disappear if we bred from the brown varieties. 
But in nature both forms are common, and therefore it 
is certain that both must be advantageous to the species, 


or one of them would quickly disappear. I -believe 
that it is a benefit to the species that some of its 
larvae should resemble brown and others green catkins, 
instead of all of them resembling either brown or green. 
In the former case the foes have a wider range of 
objects for which they may mistake the larvse, and 
the search must occupy more time, for equivalent 
results, than in the case of other species which are 
not dimorphic. 

Dimorphism is also valuable in another way : the 
widening range of a species may carry it into coun- 
tries in which one of its forms may be especially 
well concealed, while in other countries the other 
form may be more protected. Thus a dimorphic 
species is more fully provided against emergencies 
than one with only a single form. To take an ex- 
ample : the green colour of the young caterpillars of 
the Convolvulus Hawk Moth (Sphinx convolvuli) some- 
times persists, and is sometimes replaced by brown 
in the later stages. In Europe the latter form pre- 
dominates, because the creeping food-plant (Con- 
volvulus arvensis) is so small that it is safer for a large 
caterpillar to resemble the earth beneath rather than 
the small leaves on its surface. In the Canary Islands 
and Madeira, where the larva feeds on many large- 
leaved species of Convolvulus, the green form pre- 
dominates, for it is far better protected than the other 
against a continuous green background. 

This result appears to have been brought about by 


the ordinary operation of natural selection, leading to 
the extermination of the less protected variety. I 
have experimented with all the dimorphic larvae men- 
tioned above, and could not find any trace of suscep- 
tibility to the influence of surroundings, so as to lead 
to the production of the appropriate form. When 
such susceptibility is present, of course the dimorphism 
has a far higher protective value. The description of 
such cases is reserved for a future chapter. 

Occasionally the two forms of a dimorphic species 
appear at different times and correspond to the tints 
which successively predominate in the surroundings. 
At one time I thought the brown form of the Large 
Emerald caterpillar might appear rather later than 
the other, when the green catkins had been replaced 
by brown ; but further examination did not confirm 
the observations which pointed in this direction. Dr. 
Alexander Wallace, of Colchester, has, however, found 
that the moths of Bombyx cynthia which are the first 
to emerge from the pupae possess, as a rule, an olive- 
green ground colour, while those which emerge in 
September are generally of a yellow tint. These 
colours harmonise with the appearance of the Ailanthus 
leaflets at corresponding times of the year. 

Dimorphism in the Perfect Insect 

Dimorphism is also met with in perfect insects, 
and it is especially frequent in the females (see page 


302 for an example of a dimorphic male among 
spiders). Its meaning is obscure, but one of the two 
forms is generally much rarer than the other, and 
probably the older. The facts seem to point towards 
the replacement of an older by a younger form, 
because the latter is more attractive to the opposite 
sex, or because it is better concealed, or because the 
appearance is accompanied by other benefits to the 
species. The dark variety of the female Silver-washed 
Fritillary (Argynnis paphia, var. ralezina), and the 
white variety of the female Clouded Yellow (Colias 
edma, var. helice), are examples of dimorphism among 
British butterflies. I exclude that form of dimor- 
phism, or polymorphism, which is caused by one sex 
' mimicking ' two or more species which are specially 
protected (for a good example see pp. 234-38). 

An extremely important form of di- or poly- 
morphism occurs among the females of the social 
Hymenoptera. In this case, however, the different 
forms are specially fitted for certain duties, and the 
consequent division of labour is beneficial to the 
society and therefore to the species. 

Seasonal Dimorphism 

Finally, a species which passes through two or 
more cycles of development in a year, viz. one that 
is ' double ' or ' treble-brooded,' is often characterised 
by * seasonal dimorphism/ in which the first brood is 


different in appearance, and often in size, from the 
later ones. Professor Weismann has investigated this 
question, and he finds that while the later broods can 
be readily made, by the application of ice in the pupal 
stage, to assume the form of the first or winter gene- 
ration, the latter cannot be made to assume the form 
of the summer brood by the application of warmth. 
He infers that such species were single-brooded in the 
short summers which succeeded the Glacial Period, 
and that the appearance was that of the present winter 
form. As the summers became longer, other newer 
generations with a different appearance were added 
(summer broods), but the species always tends easily 
to revert to the more ancient form. An important 
part of the evidence consists in the proof that such 
species are now single-brooded hi the northern part of 
their range, and that the one form is that of the 
winter brood of more southern localities. 1 

I have given a very brief sketch of dimorphism, 
hardly alluding to polymorphism, which is only an 
extension of the same principle. Although the subject 
is only touched upon, enough has been said to show 
that there are many distinct kinds of dimorphism, 
some of which are very obscure. By far the most 
important kind of di- or polymorphism remains to be 
described below (see Chapters VIII. and IX.), in which 

1 See Studies in the Theory of Descent, by August Weismann. 
English translation by Professor Meldola. 


each individual has two or more appearances, as it 
were, at its command, and can develop that one which 
is most suited to its own peculiar surroundings. 

A reason for the wonderful concealment of Lepidopterous 

In the remarkable abundance and variety of 
methods by which concealment is effected in Lepi- 
dopterous larvae, we probably see a result of their 
peculiarly defenceless condition. A larva is a soft- 
walled cylindrical tube which owes its firmness, and 
indeed the maintenance of its shape, to the fact that 
it contains fluid under pressure, which is exerted by 
the sides of the body. This construction is extremely 
dangerous, for a slight wound entails great loss of 
blood, while a moderate injury must prove fatal. 
Hence larvae are so coloured as to avoid detection or 
to warn of some unpleasant attribute, the object in 
both cases being the same to leave the larva un- 
touched, a touch being practically fatal (see also 
pp. 175-76). 

The concealment of Pupae 

Protective Resemblance, either Special or General, 
is seen in nearly all exposed pupae, but most chrysalides 
are buried in the earth or protected by cocoons. The 
cocoons are often sufficient defence, because the silk is 
very unpleasant in the mouth ; but such protection 


only applies in the warmer weather when there is 
an abundance of insect food. In the winter, insectivo- 
rous animals are pinched by hunger, and would devour 
the pupa in spite of the cocoon. We therefore find 
that all cocoons which contain pupae during the winter 
are well concealed, either spun between leaves which 
fall off and become brown, or hidden under bark or 
moss, or constructed on the surface of bark with a 
colour and texture which renders them extremely 
difficult to detect. It is very common for particles of 
the bark to be gnawed off by the larva and fixed on to 
the outside of the cocoon. It will be shown below 
that many larvae can also control the colour of their 

Protective Resemblances in Butterflies and Moths 

The perfect insect is also commonly defended by 
very efficient methods of concealment. The under 
sides of the wings of butterflies are generally coloured 
like the surface on which the "insect habitually rests, 
and they are the only parts seen during repose. We 
can form some idea of the perfection of this conceal- 
ment when we remember the entire disappearance of 
common butterflies in dull weather. Many of them 
creep far down among thickly set leaves, while others 
rest freely exposed upon surfaces which harmonise 
with their colours. 

Perhaps the most perfect concealment attained 
by any butterfly is seen in the genus Kallima, found 


in India, the Malay Archipelago, and Africa. The 
way in which the insect is concealed has been described 
by Wallace in his ' Malay Archipelago,' and also in 
the 'Essays on Natural Selection.' The tip of the 
fore-wing is pointed like the apex of a leaf, and the 
hind-wing has a short tail like a leaf-stalk, while the 
outline of the folded wings between these extremities 
is exactly like that of a withered and somewhat 
shrivelled leaf. At rest the wings are held upright 
over the back, the head and antennae are concealed 
between them, while the tails touch the branch to 
which the insect clings by its almost invisible legs. 
Along the supposed leaf runs a distinct mark like 
a mid-rib, with oblique veining on either side. 

But dead and withered leaves are not all alike ; 
they may be almost any shade of brown, grey, or 
yellow, while they are often attacked by fungi of dif- 
ferent colours and in different places. Similarly the 
under sides of the wings of the butterfly are excessively 
variable, the different colours and markings only 
agreeing in that they all represent some familiar ap- 
pearance presented by withered or decayed leaves. 

Dead leaves are often pierced by insect larvae, and 
a detail of great interest is added to the disguise in 
the semblance of a small hole. The scales are absent 
from both sides of a certain spot on each fore- wing, 
which is therefore only covered by the thin transparent 
wing membrane. These spots come opposite to each 
other in the position pf rest, and the effect produced 


is exactly that of a hole, for the two membranes are 
BO transparent that they are completely invisible. The 
size of the apparent hole varies very greatly in the 
numerous specimens of Kallima inachis, in the Hope 
Collection at Oxford. 

The upper sides of the wings, concealed during 
rest, are dark, with a deep orange bar across the 
fore-wings. I have heard a naturalist, who is ac- 
quainted with the Indian species (Kallima inachis) in 
its natural surroundings, object to the interpretation 
afforded by Mr. Wallace, on the ground that he has 
often seen the butterfly displaying the conspicuous 
upper sides of its wings when settled, and has seen it 
resting on inappropriate surfaces. I do not think 
that this objection is fatal ; for butterflies only dis- 
play their brilliant tints during the short pauses 
between the successive flights, when they are on the 
alert and can evade their enemies by wariness and by 
the swiftness of their flight. Our own beautiful Eed 
Admiral (Vanessa atalanta), Peacock (V. Jo), and Small 
Tortoiseshell (V. urticce) similarly display their bril- 
liant colours when pausing on a flower or even on the 
ground. But during prolonged rest, when the insects 
are often semi- torpid and would be easily captured if 
detected, the wing?, are invariably held so that the 
sombre tints of the under sides are alone visible. 
Hence the display of bright colours by the Indian 
Kallima is no argument against the protective value 
of the leaf-like appearance of the under sides ; for the 


latter acts as a disguise when it is most necessary, for 
the butterfly to be concealed. It appears that the 
Malayan species (Kallima paralekta) is more cautious 
during the brief pauses between the flights ; for Mr. 
Wallace states that it frequents dry woods and thickets, 
and that it invariably settles on bushes with dry or 
dead leaves. He never saw one of these butterflies 
settle upon a flower or green leaf. 

A recent paper by Mr. .S. B. J. Skertchly ! en- 
tirely supports Mr. Wallace's statements. The author 
calls attention to the fact that leaf-mimicking butter- 
flies, of several genera in addition to Kallima, settle 
in an entirely different manner from that of other 
butterflies. While the latter gradually slacken their 
speed and settle deliberately, the leaf butterflies ' fly 
rapidly along, as if late for an appointment, suddenly 
pitch, close their wings, and become leaves. It is 
generally done so rapidly that the insect seems to 

Certain English moths are also protected by their 
resemblance to dead leaves. One of the most beautiful 
examples is afforded by the Herald Moth (Gonoptera 
libatrix), which suggests the appearance of a decayed 
red leaf sprinkled with a few white spots of fungoid 
growth ; the irregularly toothed margin of the wings 
adds to the effect. The bright eyes of the moth might 
expose the deception, but they are covered during 
rest by a tuft of hair which springs from the base of 

1 Ann. and Mag. Nat. Hist. Sept. 1889, pp. 209 et seg. 



the antennae (see fig. 14). When the moth is about 
to fly the antennae are brought forward, and the same 
action raises the tufts and uncovers the eyes. The 
moth appears in the autumn and lives through the 
winter, so that the resemblance to dead leaves is 
peculiarly appropriate. 

The Angle-shades (Phlogophora meticulosa) is also 
beautifully concealed by 
resembling a withered 
and crumpled leaf. The 
colours of the Yellow 
Underwing (Triplicena 
pronuba), as seen during 
flight, strongly suggest 
the appearance of a yel- 
low leaf whirled along 
by the wind and then 
suddenly dropping. The 
sudden swift rise and 
rapid descent are very 
unlike the flight of a 
moth. When at rest, it hides deeply amid thick 
foliage or among dead leaves on the ground ; it is 
extremely difficult to detect, and instantly rises when 

The Rev. Joseph Greene has pointed out that the 
various shades of yellow and brown are especially 
characteristic of autumn moths, while grey and silvery 
tints predominate in the winter species ; such tints 

FIG. 14. The base of left antenna of 
Herald Moth (Gonoptera libatrix), show- 
ing the tuft of hair which covers the eyes 
of the moth in the position of rest ; 
x 24-5 diameters. 


harmonise with those that are most characteristic in 
the corresponding seasons. 

The Buff-tip Moth (Pyg&ra bucephala) is very 
perfectly concealed by resembling a broken piece of 
decayed and lichen-covered stick. The cylindrical 
shape is produced by the wings being rolled round the 
body. A friend l has raised the objection that the 
moth resembles a piece of stick cut cleanly at both 
ends, an object which is never seen in nature. The 
reply is that the purple and grey colour of the sides of 
the moth, together with the pale yellow tint of the parts 
which suggest the broken ends, present a most perfect 
resemblance to wood in which decay has induced that 
peculiar texture in which the tissue breaks shortly 
and sharply, as if cut, on the application of slight 
pressure or the force of an insignificant blow. 

The excreta of birds are also very commonly re- 
sembled by moths as well as by caterpillars. This 
is the case with the little Chinese Character (Cilix 
spinula}? and with many grey and white Geometers 
which rest on the upper sides of leaves with their 
wings extended as if ' set.' In this position they 
forcibly suggest the appearance of birds' excrement 
which has fallen on to a leaf from a great height, and 
has therefore become flattened into a wide patch. In 
spite of a faithful resemblance to such an object, these 
moths possess very great beauty. 

Dr. C. M. Chadwick, of Leeds. 

* Arthur Sidgwick, Journ. of the Rugby School Nat. Hist. Soc. 


The appearance of splinters of wood is also often 
suggested by moths such as the ' Sharks ' (Cucullia) 
or Goat Moth (Cossus). Others resemble the surfaces 
of rock upon which they habitually rest (Bryophila, 
many Geometers, &c.). 

I have merely given a few striking instances of 
resemblance to objects which are of no interest to 
insect-eating animals. Numerous other examples 
might have been added, but my object is merely to 
illustrate from the Lepidoptera a principle of colour- 
ing which is of extremely wide application, viz. its 
use in aiding an organism to escape from enemies 
by the method of concealment. Abundant examples 
of this principle will be recognised by every one 
interested in natural history, among other orders of 
insects as well as the Lepidoptera, among vertebrate 
animals no less than among the invertebrate sub- 

Protective Resemblances in other Insects and in Spiders 

In the other orders of insects, the Orthoptera 
(locusts, grasshoppers, &c.) will be found to include the 
most beautiful examples of Protective Eesemblance. 
The tropical ' leaf insects ' and ' walking-stick insects ' 
belong to this order. The latter hold their limbs 
irregularly, so that the resemblance to a dead branch 
with lateral twigs is rendered all the more perfect. 


Spiders are often protectively coloured ; many ex- 
cellent examples are given by Elizabeth G. Peckham. 1 
One of the most remarkable is Ccerostris mitralis, from 
Madagascar, which sits motionless on a branch and 
resembles a woody knot. Its appearance is shown in 
fig. 15. A common Wisconsin spider, Epeira prompta, 

FIG. 15. Cceroslris mitralis in proaie; FIG. IS.Speir 

from Peckham ; after Vinson. lichen - covered" tree"- trunk ; from 


generally rests on the branches of cedar bushes, and 
closely resembles lichen (see fig. 16). Spiders are 
especially relished by insectivorous animals, so there 
is every reason for the faithfulness of these resem- 
blances. In many other cases, however, the resem- 
blance is chiefly aggressive, enabling the spider to 
approach its prey. 

1 Occasional Papers of tJie Natural History Society of Wisconsin, 
vol. i. 1889, Milwaukee, pp. 61 et seq. 




MANY of the lower Vertebrata have the power of 
rapidly modifying their colour according to the en- 
vironment, and these will be described in a future 
chapter. Such a power appears to be possessed by 
few reptiles, and by no bird or mammal. 

Protective Resemblances among Reptiles 

Our two English snakes are well concealed by 
their colours ; the olive-green Grass Snake (Tropi- 
donotus natrix) harmonising well with the grassy banks 
which it chiefly frequents; while the brown viper 
(Pelias berus) is difficult to detect upon the dry heaths 
where it is most commonly found. Our lizards are 
also well protected in the same manner. 

Protective Resemblances among Birds 

Wallace has directed attention to the protective 
colours of female birds which build open nests, and he 
points out that the males are similarly protected when 


they undertake the duties of incubation. The same 
necessity does not apply to species which construct 
covered nests or build in holes. 

The Colours and Markings of Birds' Eggs 

The protective value of the tints and markings 
of eggs are of great interest, and have not been 
sufficiently investigated. The fact that eggs are 
protectively coloured was fully recognised by Erasmus 
Darwin, who places them under ' colours adapted to 
the purpose of concealment.' He says ' the eggs of 
birds are so coloured as to resemble the colour of 
the adjacent objects and their interstices. The eggs 
of hedge-birds are greenish with dark spots; those 
of crows and magpies, which are seen from beneath 
through wicker nests, are white with dark spots ; and 
those of larks and partridges are russet or brown, like 
their nests or situations.' l This description of the 
eggs of crows and magpies is incorrect. The eggs 
of crows are greenish with umber markings; those 
of magpies pale greenish with dark markings. It is 
probable that Erasmus Darwin correctly explained 
the appearance of the eggs of the wood-pigeon (see 
p. 62), and inadvertently illustrated this principle of 
colouring by erroneous instances. The special men- 
tion of the interstices between the parts of sur- 
rounding objects, as well as the objects themselves, is 

1 Zoonomia, 1794, vol. i. p. 510. 


of great interest; protective colouring can never be 
fully understood until this principle is taken into 

In order to make out the true meaning of the 
colours of eggs they must be observed in their natural 
surroundings, and must be looked at from all points 
of view and at varying distances. It is very probable 
that the bright blue colour of certain eggs will be 
explicable under these conditions. 

The fact that concealed eggs are almost invariably 
white strongly confirms the conclusion that the colours 
of expos-ed eggs are of value to the species, and are 
maintained by the operation of natural selection. 
Certain exposed eggs may, however, be white, as in 
the wood-pigeon, but in these cases the eggs are pro- 
tected from enemies beneath ; for the holes in the 
loosely constructed nest through which they are seen 
cannot be distinguished from others through which 
the bright sky appears. 

The whiteness of eggs hidden in holes or in covered 
nests, or buried under leaves, is of a very different 
nature, for it is due to the cessation of natural selec- 
tion, perhaps aided by reversion to the ancestral 
colour, which is still preserved in the eggs of reptiles. 
All useful characters are kept up to a high pitch of 
efficiency by the continual elimination of the unfittest, 
and as soon as such elimination ceases, the level of 
efficiency must fall. This interpretation is confirmed 
by the fact that the eggs of certain species which now 


nest in the dark still retain traces of patterns which 
are well developed upon the eggs of their nearest allies 
with other habits. Thus the egg of the puffin, which 
nests in a burrow, would be called white at a little 
distance, but closer examination reveals the presence 
of very faint spots, which are distributed as in the 
very distinctly marked egg of the razor-bill. 1 Certain 
other species still lay strongly marked eggs in the 
dark, and in their case the change of habit presumably 
took place at a comparatively recent date. Such a 
conclusion can be tested by an investigation of the 
habits of closely allied species. Although white must 
have been the ancestral colour of birds' eggs, it has 
probably been re-acquired in species which nest in the 
dark. It would be very difficult to believe that such 
a habit has persisted continuously since the time when 
all birds' eggs were white. 

The strongest confirmation of this explanation of 
the whiteness of hidden eggs is, however, to be found 
in the colours of the eggs in the various breeds 
of domestic fowls. If the gradual disappearance of 
colour is due to the cessation of natural selection, we 
must expect it to occur, however the cessation has 
been brought about. Natural selection cannot operate 
to preserve the colour of eggs laid in the dark, and it 

1 This interesting example attracted my attention while looking 
over a collection of eggs in the possession of my friend, Mr. E. H. 
Greenly. Mr. H. Seebohm informs me that he has no doubt about 
the validity of this interpretation, which was suggested in hiu work 
on British Birds, 1885, vol. iii. p. 367. 


is equally inoperative when enemies are artificially 
excluded from eggs laid in open nests. And the eggs 
laid in our poultry-yards afford conclusive evidence 
that colour disappears as surely under the latter 
condition as under the former. The brown colour 
must be a very important protection to the eggs of 
the ancestor of our domestic breeds, the Asiatic jungle 
fowl (Gallus bankiva) ; while a white appearance 
would greatly add to the danger of discovery by egg- 
eating animals. But there is no such difference be- 
tween the value of white and brown in confinement, 
and we accordingly find that the colour is disappear- 
ing. Certain fowls lay white eggs, and the tint of 
those which still lay coloured eggs varies considerably, 
' the Cochins laying buff-coloured eggs, the Malays a 
paler variable buff, and Games a still paler buff. It 
would appear that dark-coloured eggs characterise the 
breeds which have lately come from the East, or are 
still closely allied to those now living there.' ' 

Erasmus Darwin further suggested that the colours 
of eggs, in common with other protective colours, may 
be due to the effect of the imagination of the female. 2 
This suggestion has been still further elaborated by 
A. H. S. Lucas, 3 but no real proof of it is brought 
forward in his paper. That eggs resemble their sur- 

1 Darwin, Variation of Animals and Plants under Domesti atiou, 
1875, vol. i. p. 261. 

2 Loc. cit. p. 611. 

Royal Society of Victoria, 1887, pp. 52-60. 


roundings is explicable by the operation of natural 
selection, while the gradual loss of colour when natural 
selection ceases to operate, is in opposition to Mr. 
Lucas's hypothesis, which assumes that the colour of 
the shell is determined by the influence of surround- 
ing tints upon the retina of the female. If the rusty 
spots on the eggs of birds of prey are due, as Mr. 
Lucas supposes, to the sight of blood, eggs laid in the 
dark should still be affected by the memory of some 
colour either predominant in the surroundings, or of 
especial interest to the female. The hypothesis might 
easily have been tested by surrounding birds with un- 
usual colours and observing the tints of their eggs : 
and, had this been done, I believe that the paper would 
not have been written. 

Since the last paragraph was printed, a letter from 
the Rev. F. F. Grensted has been communicated to 
' Nature ' by Mr. A. E. Wallace. 1 The writer believes 
that the colour of the egg of the red-backed shrike 
varies with the tint of the lining material of the nest. 
Mr. E. B. Titchener maintains that there is not suffi- 
cient evidence for this opinion. At one time Mr. 
Titchener believed that Variable Protective Resem- 
blance was exhibited by the eggs of the yellow- 
hammer and spotted fly- catcher as well as by those 
of the red-backed shrike. Further observation con- 
vinced him that the evidence was insufficient. 2 

1 Nature, vol. 41, Nov. 21, 1889, p. 53. 

2 Ibid., Dec. 12, 1889, pp. 129-30. 


The strongest argument used by Mr. Lucas is the 
fact that cuckoos at first sight appear to have the 
power of adjusting the colour of their eggs to those of 
the birds which are so successfully imposed upon. It 
seems to be certain, however, that the cuckoo carries 
her egg to the nest in her beak ; for there are numerous 
instances of the cuckoo's egg having been found in 
a nest which the bird itself could not possibly enter, 
and Mr. Lucas gives examples of the same kind from 
Australia. The cuckoo has therefore the chance of 
seeing the colour of her egg, and of carrying it to the 
appropriate nest. It is also possible that different 
individuals lay eggs of a different shade, and deposit 
them in the nests of species with eggs of a correspond- 
ing appearance. The whole relation of the cuckoo to 
the birds it deludes is most interesting, but very 
difficult to decide satisfactorily, because of the extreme 
shyness of the bird. I do not think, however, that the 
facts which .are now at our disposal afford sufficient 
justification for the opinion that the female cuckoo 
can control the colour of her eggs. 

I have discussed the colours of birds' eggs at some 
length in the hope that those readers who are interested 
in the subject may be induced to observe for them- 
selves, and assist in obtaining a far more complete 
knowledge of the meaning of the colour and marking 
of eggs than we at present possess. 

I know of no more inspiring subject than the 
colours of birds' eggs. The most superficial glance 


over a collection of eggs reveals hosts of interesting 
problems which require solution. I look forward to 
the time when any description of colour and marking 
will be considered incomplete unless supplemented 
by an account of their meaning and importance in 
the life of the species. 

Protective Resemblances among Mammalia 

Among the Mammalia it would be hardly possible 
to meet with a better example of protective colouring 
and attitude than that of the hare as it sits motion- 
less, exactly resembling a lump of brown earth, for 
which indeed it is frequently mistaken. The dark 
brown or grey colours of all our smaller quadrupeds 
are also highly protective. The change of colour in 
northern mammals in the winter will be described 
in Chapter VH 

Protective Resemblances among Fish 

The power of colour adjustment is very widely 
distributed among fish and Amphibia, and will receive 
attention in a later chapter. I will therefore only say 
a few words about the Protective Eesemblance of the 

Professor Stewart has shown me a beautiful ex- 
ample in the Australian Sea Horse (Phyllopteryx eques), 
a fish which is covered with numerous cutaneous 


appendages, most of which are supported by a bony core. 
The appendages are flat, and are alternately banded 
with dusky brown and orange, exactly resembling the 
form and colour of the sea-weed to which the fish 
clings with its tail. There also are many bony spines 
without the flat folds of skin, and these are doubtless 

The general arrangement of colour on porpoises, 
most fish, &c., has been well explained by Wallace. 
Looking down on the dark back of a fish it is almost 
invisible, while, to an enemy looking up from below, 
the light under-surface would be equally invisible 
against the light of the clouds and sky.' 1 

The white colour of one side of such fish as the 
sole, turbot, &c. (Pleuronectidce), viz. the side which 
is in contact with the sand or mud, cannot be ex- 
plained in this way. In such a case we see the dis- 
appearance of colour in consequence of the cessation 
of natural selection, as in the white eggs laid in the 
dark, while the white bellies of many fish may be 
compared to the whiteness of the eggs of the wood- 
pigeon, an appearance produced by the operation of 
natural selection. 

It has been already pointed out that natural 
selection may not only remove the pigment from an 
animal, but may oven replace the red blood of a 
vertebrate by a colourless fluid. The transparency 

1 Tropical Nature, p. 171. 


of the surface swimming fish, Leptocephalus, is in- 
creased in this way. 1 

Protective Resemblances among Marine Animals 
Before leaving this part of the subject I must 
allude to Protective Eesemblances among marine 
animals. Although large numbers of isolated cases 
are understood, the principles of colouring in marine 
forms have been very incompletely worked out. The 
difficulties are far greater than in land animals, be- 
cause it is often nearly impossible to observe the 
species in their natural environment, and it has 
been already shown that this is essential if we are fully 
to understand the meaning of all details in their 
appearance and attitudes. It is, however, very satis- 
factory to know that the whole subject of the colouring 
of marine mollusca is being undertaken in a syste- 
matic manner by Mr. W. Garstang, 2 assisted by all the 
appliances of the laboratory of the Marine Biological 
Association at Plymouth. 

Protective Resemblances among Marine Mollusca 

E. S. Morse has shown, contrary to Darwin's 
opinion, 3 that the appearances of many mollusca 
are such as to afford concealment. An extremely 

1 E. Ray Lankester, On the Distribution of Haemoglobin,' Proc. 
Boy. Soc. No. 140, 1873. 

2 Journ. Mar. Biol. Assoc., New Series, vol. i. No. 2, Oct. 1839, 
pp. 173 et seq. 

3 Descent of Man, vol. i. p. 316. 


interesting example was brought before me by Mr. 
Garstang, viz. that of the Opisthobranch mollusc, 
Hermcea, which is transparent and therefore invisible, 
except for the ' hepatic ' canals, which simulate in form 
and colour the reddish weed (Griffithsia) on which the 
animal usually lives. Mr. Garstang finds that the 
colour is purely adventitious, being due to the food 
undergoing digestion (see pp. 79, 80). Another English 
species of Hermcea is green, and lives on green weeds. 
Mr. H. L. Osborn has published a very interesting 
note on the resemblance between the colour of a coral 
on the North American coast and the mollusc which 
habitually lives upon it. 1 He states that Dr. E. B. 
Wilson, working in 1879 in Dr. Brooks's laboratory 
at Beaufort, N.C., found an orange-yellow coral 
(Leptogorgia virgulata) invariably attended by a gastro- 
pod of the same Colour (Ovulum uniplicaturri), which 
was never seen apart from the coral. Dr. Wilson's 
coral occurred in shallow water. In 1884, Mr. Osborn, 
also working at Beaufort, found a Leptogorgia in ten 
fathoms of water, of the same general habit as L. vir- 
gulata, but of a deep rose colour, almost purple. The 
ground-colour was mottled with white round the open- 
ings of the polypes. A large number of molluscs were 
found on the coral, and these had red-brown shells, with 
the surrounding skin of a deep rose colour mottled with 
white. Except for this difference in colour the molluscs 
exactly resembled 0. uniplicatum, and Mr. Osborn con- 
1 H. L. Osborn, Science, New York, 1885, vi. pp. 9-10. 


eiders that they were undoubtedly of the same species. 
When placed in an aquarium the molluscs always 
sought their own corals, but if red- molluscs and 
yellow corals were put together the former took no 
notice of the latter. 

It is very interesting to find that Mr. Garstang 
notices a similar association between species allied to 
the above at Plymouth. A reddish coral (Gorgonia 
verrucosd) is attended by a gastropod (Ovula patula) , 
adapted in form and colour for concealment on the 
stems of the Gorgonia. 

It might be argued that these are cases of Pro- 
tective Mimicry, inasmuch as one animal resembles 
a portion of another for the purpose of protection. 
Similar examples are to be found in certain parasites 
which resemble the colour of the hair or skin of 
the animal they infest. Protective Mimicry, how- 
ever, leads one animal to be mistaken for another, 
and thus to live upon the reputation of the latter. 
Protective Kesemblance simply renders an animal 
difficult to detect. Animals defended in the former 
manner are almost invariably conspicuous ; in the 
latter they are admirably concealed. Mr. Garstang 
tells me that Gorgonia is exempt from the attacks of 
fishes, so that the molluscs gain additional advantage 
by resembling an inedible form. Inasmuch as con- 
cealment appears to be the chief object of the form and 
colour, the example falls under Protective Eessmblance, 
although it leads in the direction of true Mimicry. 




Aggressive Resemblances 

PASSING now to Aggressive Resemblances, the appear- 
ance of the larger Carnivora harmonises well with 
their surroundings, enabling them to approach their 
prey. The colours of snakes, lizards, and frogs are 
doubtless Aggressive as well as Protective. Certain 
carnivorous insects, such as the Mantidae, are well- 
concealed by their colour ; and this, although chiefly 
Protective, is probably also of value in enabling them 
to creep upon their prey. Aggressive, like Protective, 
colouring may be either Special or General. 

Alluring Colouration 

Special Aggressive Resemblance sometimes does 
more than hide an animal from its prey ; it may even 
attract the latter by simulating the appearance of 
some object which is of special interest or value to it. 
Such appearances have been called Alluring Coloura- 


tion by Wallace, and they are some of the most in- 
teresting of all forms of Aggressive Eesemblance. 

An Asiatic lizard, Phrynocephalus mystaceus, is a 
good example. Its general surface resembles the 
sand on which it is found, while the fold of skin at 
each angle of the mouth is of a red colour, and is 
produced into a flower-like shape exactly resembling 
a little red flower which grows in the sand. Insects, 
attracted by what they believe to be flowers, approach 
the mouth of the lizard, and are of course captured. 
Professor C. Stewart kindly brought this instance 
before me, and showed me a specimen of the lizard 
in the Museum of the Royal College of Surgeons. 
' Similar examples are to be found among fishes. 
The Angler, or Fishing Frog (Lophius piscatorius) , pos- 
sesses a lure in shape of long slender filaments, the 
foremost and longest of which has a flattened and 
divided "extremity. The fish stirs up the mud so as 
to conceal itself, and waves these filaments about : 
small fish are attracted by the lure, mistaking it for 
worms writhing about in the muddy water ; they 
approach and are instantly engulphed in the enormous 
mouth of the Angler. This interesting habit has been 
known since the days of Aristotle. Certain deep-sea 
forms allied to Lophius behave in a similar manner, 
but as the depths of the sea are dark, they have a 
special ' phosphorescent organ, which probably illu- 
minates the play of the tentacles which serve to 
allure other creatures.' In some of these fish (certain 


species of Ceratias) the foremost tentacle bears a 
luminous organ which is suspended as a lure in front 
of the mouth. 1 The prey are attracted by the light 
into this convenient position for effecting their capture. 
An Indian Mantis (Hymenopus Ucornis) feeds 
upon other insects which it attracts by its flower-like 

PIG. n.Bymenopui bicomis in active pupa stage. 

shape and pink colour. The apparent petals are the 
flattened legs of the insect. The appearance of the 
Mantis in the active pupa stage is shown in fig. 17.- 
The figure has been copied from a drawing sent by 

1 A. Giinther, Challenger Reports, vol. xxii. p. 52, and Introduc- 
tion, p. xxx. The function of the luminous organ was first sug- 
gested by Liitken. 


Mr. Wood-Mason to Mr. Wallace, who kindly lent it 
to me. 

Another beautiful example of Alluring Colouring 
was discovered by Mr. H. 0. Forbes in Java. Butter- 
flies are often attracted by the excreta of birds, and a 
spider (Ornithoscatoides decipiens) takes advantage of 
this fact to secure its prey. The resemblance to a 
bird's dropping on a leaf is carried out with extraordi- 
nary detail. Such excreta consist of a * central and 
denser portion, of a pure white chalk-like colour, 
streaked here and there with black, and surrounded 
by a thin border of the dried up more fluid part, 
which, as the leaf is rarely horizontal, often runs for 
a little way towards the margin ' and there evaporates, 
forming a rather thicker extremity. The margin is 
represented by a film-like web, with a thickened part 
to represent the fluid which has run to the edge or 
apex of the leaf ; the central mass is represented by 
the spider itself with white abdomen and black legs, 
lying on its back in the middle of the web, and held 
in position by the spines on its anterior legs which 
are thrust under the film. 1 The whole combination of 
habits, form, and colouring afford a wonderful example 
of what natural selection can accomplish. In such a 
case there is no necessity for calling in the aid of any 
other principle, for the addition of each new feature 
and the improvement of every detail would at once 

1 H. 0. Forbes : A Naturalist's Wanderings in the Eastern Archi- 
pelago, pp. 63-65. 


give an advantage to the possessor in the constant 
struggle for food. 

Adventitious Protection 

Before proceeding to describe the power of Vari- 
able Protective Eesemblance possessed by many 
animals, it is necessary to point out that effects 
similar to those described above may be gained by 
means which supplement the acquisition of any special 
colour and form, or which may entirely replace these 
methods of producing concealment. Many animals 
cover themselves with objects which are prevalent in 
their surroundings and are of no interest to their 
enemies. Sometimes the meaning of this habit is 
concealment alone, but in other cases objects of great 
strength are selected and bound firmly together so 
as to form a resistant armour. 

Many Lepidopterous larvae live hi cases made of 
the fragments of the substance upon which they live. 
The cases of the larvae of Clothes Moths are only too 
well known ; those of the Psychidce are made of leaf 
or brown grass stems. The larva of the Essex 
Emerald Moth (Geometra smaragdaria) covers itself 
with a loose case made of fragments of leaves spun 
together with silk. The cocoons of Lepidoptera are 
frequently concealed by containing fragments of wood 
or bark gnawed off the surface on which the cocoon is 
constructed (Centra, Cilix, Hemerophila, &c.). Birds' 


nests are often similarly concealed ; the lichen- covered 
nest of the chaffinch is an obvious instance. - 

The well-known cases of Caddice-worms (Trichop- 
tera) are partly for concealment and partly for defence ; 
they are built of grains of sand, small shells (often 
alive), vegetable fragments, in fact, of any suitable 
objects which are abundant at the bottom of the 
stream in which they happen to be. 

Some of the best examples are to be found among 
marine animals. Certain sea-urchins cover themselves 
so completely with pebbles, bits of rock, shell, &c., that 
one can see nothing but a little heap of stones. 

Many marine mollusca have the samp habits, 
accumulating sand upon the surface of the shell or 
allowing a dense growth of algae to cover them. 1 The 
best example of the kind was shown me by Professor 
C. Stewart, and is all the more interesting because of 
the transition observed in the habits of different species 
of the same genus, Xenophora. Many of these gastro- 
pods include pieces of shell, rock, coral, &c., in the 
edge of the growing shell. The effect is probably to 
obscure the junction between the shell and the surface 
on which it rests, and thus to assist in rendering the 
organism difficult of detection. Thus the growth of 
the shell may be traced by a spiral line of included 
fragments (X. calculifera) . In X. Solaris the habit is 
only maintained during the early stages of growth, 

1 E. S. Morse: Proc. Boston Soc. Nat. Hist, yol, xiv. April 5, 
1871, p. 7. 



and the spiral line of fragments extends for a certain 
distance, and is then suddenly replaced by spines 
which are doubtless of value as a defence. In X. cerea 
and X. solaroides the size of the adventitious particles 
is so great as to nearly conceal the shell, while in 
X. conchyliophora nothing can be seen but a heap of 
fragments. Specimens of Xenophora and of the crabs 
mentioned below are to be seen in the Museum of 
the Eoyal College of Surgeons, as part of a beautiful 
series intended by Professor Stewart to illustrate the 
various uses of the colours of animals. 

The tube of certain well-known marine worms 
(Terebellida) is constructed of sand-grains cemented 

One of the most interesting examples of adventi- 
tious protection is afforded by certain crabs (Steno- 
rhynchus, Inachus, Pisa, Mala) , which fasten pieces of 
sea-weed, &c., on their bodies and limbs. Bateson 
has watched the process in Stenorhynchus and Inachus. 
1 The crab takes a piece of weed in his two chelae, and, 
neither snatching nor biting it, deliberately tears it 
across, as a man tears paper with his hands. He 
then puts one end of it into his mouth, and, after 
chewing it up, presumably to soften it, takes it out 
in the chelae and rubs it firmly on his head or legs 
until it is caught by the peculiar curved hairs which 
cover th m. If the piece of weed is not caught by 
the hairs, the crab puts it back in his mouth and 
chews it up again. The whole proceeding is most 


human and purposeful. Many substances, as hydroids, 
sponges, Polyzoa, and weeds of many kinds and 
co 1 our s, are thus used, but these various substances 
are nearly always symmetrically placed on corre- 
sponding parts of the body, and particularly long, 
plume-like pieces are fixed on the head, sticking up 
from it. ... Not only are all these complicated 
processes gone through at night as well as by day, 
but a Stenorhynchus if cleaned and deprived of sight 
will immediately begin to clothe itself again, with the 
same care and precision as before.' 1 Bateson states 
that Stenorhynchus does not betray any disposition to 
remain in an environment which harmonizes with its 

Adventitious Colouring 

The protective colouring of many animals may be 
due to the food in some part of the digestive tract, 
seen through the transparent body. This is impor- 
tant in many transparent caterpillars, such as the 
Noctuce, and probably in many marine organisms. If 
a larva, such as that of the Angle-shades (Phlogophora 
meticulosd), be fed on the orange- coloured marginal 
florets of the marigold, the passage of food along the 
alimentary canal can be distinctly traced by the pro- 
gressive change in the colour of the caterpillar. 

The green colour of the blood of most larvae is 

1 Journ. Mar. Biol. Assoc., New Series, vol. i. No. 2, Oct. 1889, pp. 


adventitious in origin, having been derived from the 
chlorophyll of the leaves ; it is, however, much modi- 
fied in constitution by the time it reaches the blood. 
The green colouring matter passes from the blood 
into the cells of the surface of the body in many 
caterpillars, but is re-dissolved in the blood of the 
chrysalis. It is then made use of, in certain species, 
to tinge the eggs, and, after this, is absorbed into the 
body of the young larvae which afterwards hatch from 
them, protecting them with a green colour before they 
have had time to acquire fresh chlorophyll from the 
leaves. The passage of an adventitious colouring 
matter on into a second generation is a very remark- 
able phenomenon. There does not, however, seem to 
be any doubt about its occurrence in certain species 
(e.g. Smerinthus ocellatus) , l and I have a good deal of 
unpublished evidence on the subject. 

1 See ' Proceedings of Physiological Society,' pp. xxv and xxvi, 
in Journal of Physiology, vol. viii. 1887. 



PROTECTIVE Resemblance in its highest and most per- 
fect form must not be fixed, but capable of adjustment, 
so that the animal is brought into correspondence 
with each of the various tints which successively form 
its environment, as it moves about. An active and 
wide-ranging animal will be benefited by the power 
of resembling the tints of many different environments, 
and by that of changing its colour rapidly. 

More sluggish animals only require the power of 
bringing their appearance into harmony with a single 
environment, although the capability of adjustment 
is still of great value, because the environments of the 
different individuals vary, at any rate to a slight 
extent. Thus a moth lays some of its eggs upon one 
tree of a certain shade of green, and others upon 
another with leaves of a rather different shade ; so that 
the caterpillars would not have same environment, and 
would gain, by possessing the power to adapt their 
colours. At the same time there would be no im- 


perative necessity for the change to be extremely 

In other cases it will be of advantage to the animal 
to possess the power of changing twice in its life, once 
for the peculiar surroundings of the caterpillar, and 
once for the peculiar surroundings of the chrysalis. 
There is indeed some ground for the belief that in 
certain cases the colours of the perfect insect also may 
be adjusted to correspond with the peculiar environ- 

Variable Protective Resemblance in Fishes 

Instances of the power of rapid adjustment are 
very common, although most people are not aware of 
them. Nearly all fishermen know that the trout 
caught in a stream with a gravelly or sandy bottom 
are light-coloured, while those caught in a muddy 
stream are dark. It is also well known that the same 
fish will soon change in colour when it passes from one 
kind of background to the other. Thus Mr. E. D. Y. 
Pode tells me that all the trout in a stream near Ivy 
Bridge have become unusually light ever since the 
pollution of the stream by white china clay. 

The same facts are true of many other freshwater 
and sea fishes. The interior of a minnow-can is 
painted white in order that the bait may become light- 
coloured and thus conspicuous in the dark water where 
the pike or perch is likely to be found. The change 
of colour occupies an appreciable time, and the fisher- 


man knows that he stands an extra chance of catch- 
ing his fish while the bait remains unadapted to its 
environment. This experience serves to prove in a 
practical way that the power of changing the colour is 
essentially protective. 

Variable Protective Resemblance in Amphibia 

Other animals possess the same power. The Com- 
mon Frog (Rana temporaria) can change its tints to a 
considerable extent. Thus Sir Joseph Lister states 
that ' a frog caught in a recess in a black rock was 
itself almost black; but after it had been kept for 
about an hour on white flagstones in the sun, was 
found to be dusky yellow with dark spots here and 
there. It was then placed again in the hollow of the 
rock, and in a quarter of an hour had resumed its 
former darkness. These effects are independent of 
changes of temperature . . .' l The Green Tree Frog 
(Hyla arborea), so common in the South of Europe, 
is bright green when seated among green leaves, but 
becomes dark-brown when resting on the earth or 
among brown leaves. It is very interesting to notice 
that when this frog turns brown, irregular spots 
become conspicuous upon its skin, spots which evi- 
dently correspond to those upon the Common Frog 
(Rana), but which are invisible when the green tint is 

1 Lister : Phil. Trans., 1858, vol. 148, p. 628. 


Variable Protective Resemblance in Reptiles 

The power of Variable Protective Eesemblance is 
therefore present among fish and Amphibia, but the 
most remarkable and well-known example is afforded 
by a reptile, the Chamaeleon. The rapidity with 
which the change of colour takes place, and the wide 
range of tints which the animal has at its command, 
have caused this lizard to be regarded as a type of 
everything changeable. But the same power is also 
present in certain of the South American lizards- 
belonging to the family Iguanidce, and it is probable 
that Variable Protective Eesemblance is much more 
common than has been generally supposed. 

The changes of colour depend upon the eye 

The physiological mechanism by means of which 
these rapid changes of colour are effected has been 
investigated by Lister in this country, by Briicke in 
Germany, and by Pouchet in France. At first sight 
it appears likely that the light may directly determine 
the distribution of colouring matter in the pigment 
cells in or immediately beneath the skin. Each of 
the various surroundings of an animal would, accord- 
ing to its colour, reflect light of a certain constitution, 
and it might well be supposed that each kind of re- 
flected light would produce a different effect upon the 


pigment cells. It is, however, now well known that 
the action is extremely indirect; certain kinds of 
reflected light act as specific stimuli to the eye of the 
animal, and differing nervous impulses pass from 
this organ along the optic nerve to the brain. The 
brain being thus indirectly stimulated in a peculiar 
manner by various kinds of reflected light, originates 
different impulses, which pass from it along the nerves 
distributed to the skin, and cause varying states of 
concentration of the pigment in the cells. The highest 
powers of the microscope, assisted by ah 1 the varied 
methods of histology, have failed to detect the con- 
nection between the nerves and the pigment cells in 
the skin, and yet such connection appears to be ren- 
dered certain by the fact that light falling on the e$B 
modifies the distribution of the pigment granules. 

The pigment cells in the skin are often of various 
colours, and are 'arranged in layers, so that very 
different effects may be produced by concentration in 
certain cells, leading to the appearance of those of 
another colour, or to a combined effect due to the 
colours of two or more kinds of cells. 

Blind animals cannot vary their colour protectively 

It has been shown by experiment that blinded 
frogs have no power of altering their colour so as to 
correspond with surrounding tints. The same facts 
also have been proved in a most interesting manner 


by the observation of living animals in their natural 
surroundings. Thus Pouchet noticed that one single 
plaice out of a large number upon a light sandy 
surface was dark-coloured, and thus unlike its sur- 
roundings. Examination showed that this individual 
was blind, and therefore unable to respond to the 
stimulus of reflected light. 1 

Another very interesting example of the same kind 
was brought under my notice by my friend, Mr. H. 
Nicoll. This gentleman had observed that in addition 
to the light- coloured trout usually seen in a chalk 
stream in Hampshire (a tributary of the Test), very 
dark individuals are occasionally met with. He was 
puzzled for a long time, but the fact that the dark 
fish could never be induced to rise to a fly finally led 
him to examine them, when he found that they were 
invariably blind, the crystalline lens being opaque. 
Sometimes the fish were blind in one eye, but this did 
not affect their colour. The darkness appears to come 
on gradually with increasing blindness, for the depth 
of the tint varies in different individuals, and some- 
times only part of the body (e.g. the tail) is affected. 
The blindness probably comes on with age, for the 
dark fish are always large, generally between one and 
two pounds in weight. 

1 Quoted by Semper, Animal Life, International Scientific Series, 
pp. 95-9ti. 


The power of varying the colour essentially protective 

The protective value of the change of colour in 
normal trout was especially well seen when contrasted 
with these blind individuals. As it has been some- 
times asserted that protection is not the meaning 
of resemblance to the environment, I was anxious to 
observe so striking a contrast for myself. Mr. Nicoll 
kindly gave me the opportunity of seeing the fish in 
his stream, and I can in every way confirm his state- 
ment that a person unaccustomed to the observation of 
animals would certainly fail to detect any trout except 
the black ones. No one who had the opportunity of 
comparing the changing colours of the normal fish 
ever harmonising with their surroundings, with the 
unvarying conspicuous darkness of the blind in- 
dividuals, could hesitate for a moment in admitting 
that concealment is the one object of the adjustment 
of colour. 

The change of colour may also be voluntary or 
may follow from mental excitement. Thus the colours 
of fish often become much brighter while they are 
feeding. 1 

The food of blind trout 

It may be objected that the dark fish still continue 
to live in the same stream with the more perfectly 

1 For a carious change of colour in the conger, see Bateson, Ix. 
pp. 214-15. 


concealed individuals. This is sufficiently explained 
by the facts that the waters are carefully preserved, 
and that the blindness only comes on when the fish 
are large, and are therefore exposed to the attacks of 
comparatively few enemies. 

Mr. Nicoll informed me that the black fish were 
usually in very poor condition, and I was very anxious 
to ascertain the kind of food which was still accessible 
to them. We therefore caught two fine specimens 
which were in fair condition. I opened them and 
found their stomachs quite full of caddice-worms, 
cases and all, together with a few fresh-water shrimps 
(Gammarus), These animals are doubtless hunted by 
scent and touch, while the insects on the surface of 
the water can only be obtained by sight. 1 

Loss of power of varying colour in a chameleon 
before death 

The changes which took place in a chamaeleon in 
my possession probably show the dependence of the 
power of adjustment upon the state of the nervous 
system. In the summer, while the lizard was healthy 
and had an abundance and variety of insect food, it 
was dark-coloured by day, when it rested on some 
dark branches or walked about in its shaded cage. 
Placed upon a leafy branch in strong light it became 

1 Certain fish habitually seek their food by the olfactory and 
tactile senses. See Bateson, I.e. p. 214. 


yellowish-green in a very short time, the change 
beginning in a few seconds. At night when it was 
asleep it became light and straw-coloured. In the 
winter it died, probably on account of the scarcity 
and monotony of the only insect diet which could be 
obtained for it. For many days before its death it 
became almost black and lost all power of changing its 
colour. Its weakened nervous system either ceased to 
respond to the influence of light, or was unable to pro- 
duce any effect upon the pigment cells, which were thus 
paralysed, with their pigment permanently diffused. 
Green frogs also generally become dark before they die. 

Explanation of darkness of blind animals 

Some authorities have maintained that an animal 
of a kind which possesses the power of altering its 
colour should, when blind, become light- instead of 
dark-coloured. When the skin is light-coloured the 
pigment in the cells is strongly contracted, so that the 
coloured surface contributed by each cell occupies but a 
small space, and produces but little effect ; when the skin 
is dark the coloured parts of the cells are relaxed, and 
stretch out into the long branching processes, so that 
each dark surface becomes as large as possible. The 
latter is evidently the condition of rest, while concen- 
tration is the state of activity. It is therefore to be 
expected that when the coloured parts of cells are 
cut off from all stimuli, they will be permanently 


relaxed, so that the skin will be dark ; and we have 
seen that such a result actually occurs. When a 
muscle is cut off from nervous stimuli it also enters 
a condition of permanent rest or relaxation. Thus 
when the face is paralysed on one side, the muscles 
are relaxed and unable to balance the contraction of 
those on the other, so that the face is drawn over 
towards this latter side. The contractions of a muscle 
cell and those which take place in a pigment cell are 
not essentially different ; the former are far more 
specialised and powerful, but both of them exhibit 
manifestations of that contractile power which is 
possessed by the simplest cells. It is therefore of 
interest that both should behave in a similar manner 
when cut off from the nervous system which provides 
the stimuli under which both normally contract. In 
1858, Sir Joseph Lister showed that the coloured 
part of a pigment cell contracts independently of the 
cell itself. Cells are now recognised as composed of 
a network containing a glassy substance in its meshes ; 
pigment granules are only contained in the network, 
and, as this contracts, it carries them inwards from 
the long branching processes towards the centre of 
the ceU. 

Loss of colour in cave-dwelling animals 

On the other hand it has been argued that the 
Proteus, a blind amphibian living in the underground 
rivers of Carniola, and Carinthia, is light-coloured, 


and that other blind animals living in dark caverns 
are often white. In the majority of cases this result 
is undoubtedly due to the gradual disappearance of 
the useless pigment, and not to the excessive con- 
traction of the structures in which it is usually con- 
tained. Just as the useless eye has become rudi- 
mentary in these animals, so has the useless colour 
gradually disappeared from the skin. The energy 
necessary for the production and maintenance of such 
structures has been diverted, either wholly or in 
part, to other and more useful ends. In the Proteus, 
however, the degeneration is as yet incomplete, for the 
skin still retains pigment cells. An individual now in 
my possession has gradually become much darker since 
its removal from the cave at Adelsberg. It is probable 
that this result has followed from the direct effect of 
light upon the skin ; for it is known that superficial 
pigment cells are sensitive to light, although the 
changes of colour thus induced differ from those caused 
indirectly through the nervous system, in the absence 
of any harmony with the colours of the environment. 
The skin of the Proteus is probably extremely sensitive 
to light. By day the animal in my laboratory always 
lies concealed beneath a plate at the bottom of the 
aquarium, while ife comes out every night and swims 
freely about. As the eyes are very degenerate and 
buried beneath the surface, it appears certain that the 
difference between light and darkness is appreciated 
by the skin. W. Bateson has shown that blind 


shrimps and prawns bury themselves in the sand by 
day and swim about at night, exactly like the uninjured 
animals. 1 

The seasonal change of colour in northern mammals 

The well-known fact that many northern quad- 
rupeds become white in winter has given rise to a 
great deal of discussion as to the manner in which 
the change is brought about. Some have maintained 
that the animals simply acquire a new coat of white 
hair which conceals the darker fur beneath, while the 
long hairs of the summer coat are believed to be shed. 
Others believe that these latter actually change and 
become white, and that, although an abundance of 
new hairs also appear, nothing is shed. Most ob- 
servers agree that the white hair is shed at the close 
of winter : this is of course independently neces- 
sary, in order to reduce the thickness of the winter 

I shall bring forward what appears to be conclusive 
evidence that the latter view is the right one, at any 
rate for certain species. But however the change is 
brought about, it will be rightly considered in this 
part of the subject, if it can be proved that it is called 
up either directly or indirectly by the stimulus pro- 
vided by the external conditions, and is not merely a 
contemporaneous change, harmonising with those in 

1 L.c. p. 212. 


the surroundings. The simplest view to take of the 
matter would be to suppose that natural selection has 
favoured an extra growth of hair of a white colour for 
the winter season, so that if an animal were trans- 
ported to the equator, a similar change would take 
place at a corresponding time. If the change was 
thus merely contemporaneous and without any actual 
physiological relation to the surroundings, it would 
require discussion in the previous chapters, for it 
would be precisely parallel to the darkening of the 
larva of the Privet Hawk Moth, which takes place 
whether it will descend upon brown earth with which 
it will harmonise, or green turf against which it will 
be conspicuous (see pp. 42-43) , It is possible that the 
change of certain purely Arctic animals is of this 
kind ; but it must be remembered that many such 
animals range southward into districts where the 
white coat would be conspicuous in whiter, so that 
the higher power of Variable Protective Resemblance 
would be very beneficial. 

The question is, however, one of evidence, and I 
shall show that in certain species the change in 
colour is physiologically associated with the conditions, 
like the change in the colour of a fish which depends 
on the reflected light entering its eye. A discussion 
of the probable nature of the physiological association 
is better deferred until after considering the evidence. 


Sudden change of colour determined by sudden 
exposure to extreme cold 

A classical experiment made by Sir J. Boss, con- 
siderably over fifty years ago, seems decisive on the 
above-mentioned point, as far as the species ex- 
perimented upon is concerned. A Hudson's Bay 
Lemming kept in the cabin, and thus shielded from 
the low temperature, retained its summer coat through 
the winter : ' It was accordingly placed on deck in a 
cage on February 1, and next morning, after having 
been exposed to a temperature of 30 below zero, the 
fur on the cheeks and a patch on each shoulder had 
become perfectly white. On the following day the 
patches on each shoulder had extended considerably, 
and the posterior part of the body and flanks had 
turned to a dirty white ; during the next four days the 
change continued but slowly, and at the end of a week 
it was entirely white, with the exception of a dark 
band across the shoulders, prolonged posteriorly down 
the middle of the back. . . .' No further change took 
place, and the lemming died of the cold on February 
18, the thermometer having been between 30 and 
40 below zero every night. 'On examining the 
skin it appeared that all the white parts of the fur 
were longer than the unchanged portions, and that 
the ends of the fur only were white so far as they 
exceeded in length the dark-coloured fur; and by 


removing these white tips with a pair of scissors it 
again appeared in its dark summer dress, but slightly 
changed in colour, and precisely the same length as 
before the experiment.' l 

This experiment conclusively proves, (1) that 
the external condition itself provides the cause which 
brings the appropriate change in colour; for the 
animal did not change until subjected to the con- 
dition ; 2 (2) that in all probability the cause is a 
lowered temperature acting upon the skin ; (3) that 
the existing dark hairs become white at the tips ; for 
we cannot well believe that a fresh growth could have 
overtopped the existing hair in a single night ; (4) that 
the whitening hairs grow suddenly and rapidly. 

Nature of the change of colour in the American Hare 

The same conclusions are also supported by some 
extremely careful observations conducted by F. H. 
Welch upon the American Hare (Lepus Americanus) 
in New Brunswick. 3 In the latter district the animal 
keeps its winter coat till May, when it is gradually 
shed, the change being complete in June. The winter 
coat gradually develops in October and November, and 

1 Sir J. Ross : Appendix to Second Voyage, Nat. Hist. p. xiv. 

2 This conclusion is also supported by the fact that such changes 
occur earlier when the winter is exceptionally early. Concerning 
the Alpine Hare, see Tschudi, Thierleben der Alpenwelt, p. 300. 

Proc. Zool. Soc. 1869, p. 228. 


is retained from December till the end of April. The 
appearance of the back and sides in summer is ' glis- 
tening fawn-colour interspersed with black, especially 
over the vertebral ridge.' The colour is conferred by 
long thick hairs (the pile) covering a woolly under- 
growth of a slaty colour. 

Early in October the first changes appear ; the 
whiskers become white at the tip or in some part of 
the shaft, and a few of the longer hairs on the back 
also become white at the tip or throughout. At this 
time there is no addition to the summer coat, only a 
change in the colour of existing hairs. The changes 
advance during November, and on separating the fur 
a new growth of stiff white hairs is seen over the sides 
and back : these grow rapidly, while the long hairs of 
the summer coat also grow and become white very 
quickly as soon as the new hairs appear on the surface. 
* The shaft of the hair of the new growth is invariably 
white, a circumstance which renders it easily distin- 
guished from the autumnal hair in process of change.' 
This change is most frequent at the tip, proceeding 
downwards, but it sometimes begins in the middle, 
and occasionally at the base. ' The whiskers, which 
apparently do not lengthen but merely alter in colour, 
will demonstrate each variety. 

' Thus the whiter hue would appear to be brought 
about by a change of colour in the pile of the autumnal 
coat, combined with a new hybernal white crop, the 
latter undoubtedly playing no small part in the 


colouring process and in the thickening of the fur. 
There is no indication of shedding : an increase in 
length ensues over the whole body.' 

There is considerable individual difference in the 
time of change : it sometimes commences before the 
first fall of snow, indicating that the stimulus is the fall 
of temperature affecting the skin rather than the 
colour affecting the eyes. Great differences are seen 
when the same species is followed into other localities. 
' On the seaboard it (the winter change) is postponed 
in comparison with inland districts in the same lati- 
tudes.' In Hudson's Bay Territory it changes early 
and carries the winter coat till June, while no change 
of colour takes place in the winter in the southern 
parts of the United States. An individual kept in a 
warm barn at St. John's, New Brunswick, retained the 
summer colours. 

The consideration of the Hudson's Bay Lemming 
and the American Hare lead to the conclusion that all 
species in which the northern change does not occur 
in the southern individuals, possess the power of Vari- 
able Eesemblance. It is possible that the change is 
merely contemporaneous when it occurs uniformly in 
all individuals of the species, and it is at any rate 
probable that it would soon become so, because the 
extreme complexity of the mechanism by which Vari- 
able Resemblance is brought about would need the 
constant operation of natural selection to keep it in 


a state of efficiency. This consideration is better 
deferred until after the probable nature of the 
mechanism has been discussed. 

The physical cause of the change of colour 

It is now necessary to inquire into the actual 
physical cause of the change in appearance. It has 
already been explained that the dark colour depends 
upon absorption, while the whiteness depends upon 
scattering of light. The former is occasioned by 
pigment granules, the latter by included gas bubbles. 
When the latter are sufficiently abundant, the hair 
becomes white in spite of the pigment ; if then the 
gas were absorbed the dark colour would be restored. 1 
It appears to be well authenticated that in certain 
cases patches of human hair have become white 
during some nervous attack, again becoming dark at 
its cessation. Such changes can be explained by the 
evolution of gas (probably carbon di-oxide) at the base 
of the hair, and its subsequent absorption (probably 
by some alkaline fluid). It is therefore probable that 
the nervous system can so modify the processes taking 
place in the cells at the base of the hair as to cause 

1 This explanation only applies to the existing dark hairs which 
become white. It is very improbable that any pigment exists in the 
new hairs which make up the great part of the winter coat. Hence, 
in testing the explanation offered above, the hairs must be selected 
with the greatest care, and the investigation should be conducted in 
connection with an experiment like that of Sir J. Boss (see pp. 94-96). 


the formation of gas bubbles. The many recorded 
cases of hair turning white in a few hours as the 
result of some strong nervous shock are to be explained 
in the same manner. . 

That the change in the long autumnal hairs of 
Lepus Americanus is due to the appearance of large 
numbers of bubbles is rendered probable by an exami- 
nation of Welch's figures and descriptions. He speaks 
of the white part of a hair being much broader than 
the coloured part, and containing additional rows of 
'cells.' His 'cells' appear to be bubbles of gas, 
and he draws them with the characteristic dark 
borders. It must be remembered that the dark parts 
of a hair also contain bubbles, although in smaller 

The change in the hair is indirectly caused by the 
change of temperature 

It is extremely improbable (to say the least) that 
such changes as the evolution of bubbles, and above 
all, the growth in length, are the direct result of a 
lowered temperature on the hair itself. That they 
are indirect results, through the nervous system, is in 
every way probable, and is furthermore in harmony 
with certain well-known facts concerning the regula- 
tion of temperature. 

The direct tendency of cold is clearly to diminish 
the activity of those processes upon which the pro- 


duction of heat depends, just as it would tend to 
dimmish rather than promote the growth of hair. 
This direct effect is obvious in animals which are un- 
injured by variations of temperature. ' The body of 
a cold-blooded animal behaves in this respect like a 
mixture of dead substances in a chemist's retort : 
heat promotes and cold retards chemical action in 
both cases.' But the higher vertebrates are warm- 
blooded (homothermic), and such direct effects of cold 
would be fatal. ' In these animals there is obviously 
a mechanism of some kind counteracting, and indeed 
overcoming, those more direct effects which alone 
obtain in cold-blooded animals.' The influence of 
cold upon the nerves of the skin constitutes a stimulus 
to that part of the central nervous system which 
regulates the production of heat : thus cold indirectly 
increases the amount of heat, and the temperature 
of the body remains constant. I may mention that 
the amount of heat produced in the body at any one 
time may be gauged by the amount of oxygen ab- 
sorbed in respiration. 1 

It is in every way probable that such changes in 
colour as that of Sir J. Boss' Lemming and the 
American Hare are also indirectly caused by the cold, 
which we may suppose acts as a stimulus to that part 

1 For a further account of the regulation of temperature see 
Professor MichaeT Foster's Physiology, from which the quoted 
sentences are taken. I owe the correct understanding of the physical 
cause of the change of colour to a conversation with Professor 


of the nervous system which presides over the nu- 
tritive and chemical changes involved in the growth 
of hair and the appearance of the bubbles. 

Probable variation in susceptibility to stimulus of 
cold in different districts 

In the northern part of an animal's range, natural 
selection would favour great delicacy in the adjustment 
of the mechanism by which such changes are produced, 
so that the winter coat would be ready in time to 
harmonise with the mantle of snow. Conversely, 
extreme delicacy would be a disadvantage in the 
southern part of the range, if the climate were such 
that the snow did not lie on the ground for any great 
part of the winter. There is abundant evidence of 
variations in the delicacy of adjustment, upon which 
natural selection could operate. 

Mr. F. E. Beddard has directed my attention to 
three Arctic Foxes (Cam's lagopus) from Iceland, which 
have been in the Zoological Gardens since 1887. 
One l of these turns perfectly white every winter, while 
the other two remain dark. 

The stoat always becomes white in the alpine 
districts of Scotland,' frequently in the north of Eng- 

1 When I examined this fox on October 14, 1889, the change in 
colour was nearly complete : there was, however, a grey patch of hair 
on the back which was certainly moulting. It is possible, therefore, 
that the change is effected in an entirely different manner in this 



land, occasionally in the Midlands, and Mr. Couch 
has seen two white stoats in Cornwall. 1 It would be 
extremely interesting to take a number of Scotch 
stoats to Cornwall and an equal number of Cornish 
stoats to Scotland, in order to test whether the 
southern individuals are less susceptible to change 
than the northern. It is likely that the great differ- 
ence is not wholly to be explained by the relation of 
northern to southern temperature, but at any rate 
partially by the fact that the change is disadvantageous 
in most parts of England ; for it would render the 
animal conspicuous against the prevalent tints of a 
midland or southern winter. Of course, any such 
disadvantage implies that natural selection would 
gradually blunt the susceptibility of the apparatus by 
which the change is produced. The rare cases of 
a change of colour in Cornwall are probably examples 
of a formerly beneficial susceptibility, as yet unaltered 
by natural selection. 

Loss pf susceptibility to stimulus of cold in animals 
which remain white all the year 

Such a nervous mechanism as that to which I have 
alluded, would be of the highest intricacy and com- 
plexity, and would speedily lose its efficiency unless 
constantly preserved by natural selection. Thus 
certain Arctic animals which remain on the snow 

1 Boll : British Quadrupeds, second edition, pp. 196-201. 


nearly all the year retain the white coat permanently, 
and there is no need for the mechanism by which the 
change is produced. And yet in certain species we 
may feel sure that such a mechanism existed under 
former conditions. Thus the Arctic Hare (Lepus 
glacialis) usually remains white all the summer ; oc- 
casionally, however, it becomes greyish, the change 
of colour being limited to the points of the hair : 
the young are born grey, but change to white at 
their first winter (Welch). The latter change 
appears to be independent of cold, for Sir J. Boss 
speaks of a young hare turning white as early as 
those running wild, although in a temperature not 
much below freezing. This observation forms an in- 
teresting contrast with the behaviour of species pos- 
sessing an efficient nervous mechanism (the Hudson's 
Bay Lemming and the American Hare) when shielded 
from a low temperature. 

The white winter coat chiefly for concealment, but 
may also help to retain heat 

Certain northern animals, especially those fre- 
quenting trees, do not become white in winter : this 
is true of the Glutton (Gulo luscus). Occasionally 
dark winter individuals occur in species which as a 
rule change their colour regularly : thus, a black 
Arctic Fox is well known, but its rarity (Sir J. Eoss 
found three individuals out of fifty white ones) prob- 


ably indicates that it is, as we should expect, at a 
disadvantage, and that it will disappear. Mr. Wallace 
considers that the dark colour of arboreal northern 
animals, which is clearly for concealment, disproves 
the theory that the white colour is of value in retain- 
ing animal heat. But it does not follow that such 
benefits are wholly non-existent, because they must 
be dispensed with under the pressure of a stronger 
necessity. Mr. Wallace's argument shows that con- 
cealment is the paramount necessity ; but this does 
not disprove the opinion that other advantages also 
may be conferred by one particular mode in which 
concealment is attained. 

The seasonal change of colour in northern birds 

The same convincing evidence as to the nature of 
the .change, and the manner in which it is brought 
about, has not yet been brought forward hi the case 
of birds. Mr. A. H. Cocks, who has had a very wide 
experience of northern animals, believes that it is at 
least partially due to a change in the autumnal 
feathers. He writes : ' I have some specimens of 
Lagopus (various species) showing brown feathers 
with white tips, and in one species, at any rate, the 
converse.' Mr. E. Bowdler Sharpe does not however 
think that the evidence of a winter change in existing 
feathers is sufficient. 1 He has nevertheless proved 

1 H. Seebohm thinks it ' possible that the white winter feathers 


that other changes of colour do occur, as will be seen 
in the following passage from his most interesting 
paper. 1 

' Let any one who doubts the possibility of mark- 
ings such as those on the Greenland Falcon becoming 
gradually changed without an intermediate moult, 
study the changes exhibited by the common Sparrow 
Hawk in its progress towards maturity. The general 
characteristic of the species of Accipiter is to have a 

striped plumage when young and a barred dress when 
old. But it is not- generally known that this is 
effected by a gradual change in the markings of the 
feather, and not by an actual moult. On the first 
appearance of the feathers from the downy covering 
of the nestling, the markings on the chest are longi- 
tudinal drops (fig. 18) of a pale rufous-brown colour. 
The gradual dissolution and breaking up into three 
bars is shown in fig. 19. Hence, when the bars are 
perfectly developed a shade of darker brown over- 

(of Ptarmigan) gradually change colour in spring, only those being 
moulted which have been injured in winter.' British Birds, vol. ii. 
p. 427, n. 

1 Proc. Zool. Spc. 1873, pp. 414 et sec[. 


spreads the upper margin, gradually eclipsing the 
rufous-brown shade, which remains the evidence of 
the previous plumage (fig. 20). Hence are shown 
two successive stages of the development of the dark 
brown shade which at last removes all traces of the 
reddish tint (figs. 21 and 22).' 

If the winter change does not occur in the 
autumnal feathers, it by no means follows that 
the power of Variable Eesemblance is absent. The 
growth of new white feathers may be indirectly due 

to the cold, acting through the medium of the nervous 
system. This is, however, very far from being proved ; 
for it does not appear to be certain that there is a 
single species becoming white in winter which retains 
its dark colour at this time of the year in the southern- 
most part of its range. 

Mr. A. C. Billups, of Niagara, Ontario, tells me 
that during an exceptionally mild winter, about 
seven or eight years ago, neither the ' snow bird ' 
nor the American Hare acquired the winter dress. 
Hence the power of Variable Resemblance appears to 
be possessed by certain birda. 


Variable Resemblance of northern animals most nearly 
related to that of certain insects 

The acquisition of a special winter covering as a 
response to the stimulus of cold is most nearly related 
to the Variable Eesemblance exhibited by many cater- 
pillars and chrysalides. It will be shown in the next 
chapter that these latter changes are similar to the 
above in that the stimulus (of reflected light) acts 
upon the skin ; that the results are in all probability 
indirect, and take place through the part of the 
nervous system which regulates the production of 
colour ; finally, that far greater time is required for 
the accomplishment of the change than in those 
animals in which the stimulus acts upon the eye, and 
in which existing pigments are arranged instead of new 
substances elaborated. 

Rapid adjustment of Colour in certain invertebrate 

Certain invertebrate animals, however, possess the 
power of rapidly adjusting their colour to that of their 
surroundings. It is well-known in Crustacea, and is 
probably very common among them. The power has 
been proved to depend upon the eye as among the 
vertebrates. Some cuttle-fish also can modify their 
colours in the same manner, with remarkable pre- 


cision and rapidity. The resemblance between 
certain individuals of Ovulum and the rose-coloured 
coral, and between other individuals and the yellow 
coral (see pp. 70-71), is probably due to the existence 
of a power of adjustment ; but this suggestion needs 
experimental verification. A fact mentioned by Morse 
is even more convincing : he states that individuals 
of the same molluscan species occupying different 
stations are differently coloured, and he quotes from 
Dr. A. A. Gould the observation that the colour of all 
the shells found in the sandy harbour of Provincetown 
is remarkably light. 1 There is no evidence as to 
whether the change in colour, if produced at all, takes 
place rapidly or slowly ; but the latter is the more 
probable in these animals. 

Professor Stewart found four or five bright red 
individuals of the Nudibranchiate mollusc Archidoris 
tuberculata in a mass of bright red sponge (Hymenia- 
cidon sanguined) upon which they were feeding. 2 
The colour was very different from that of individuals 
taken upon another sponge (Halichondria) . The ob- 
servation strongly suggests the existence of a power of 
Variable Protective Eesemblance, although it is possible 
that the colour of the food may be made use of. 

It is very likely that Variable Eesemblance will 
be found to occur far more generally than has been 
hitherto supposed. 

1 Proc. Boston Soc. Nat. Hist. vol. xiv. April 5, 1871. 

2 W. Garstang, l.c. p. 177. 


Variable Resemblance, Protective and Aggressive 

As in so many other cases, the specialised form of 
concealment by the organism resembling its surround- 
ings treated of in this chapter may be either Protective 
or Aggressive ; it may enable an animal to escape its 
enemies or to approach its prey unseen. Frequently 
it may be turned to both uses by a single animal. 
Thus the green tree frog is probably aided in cap- 
turing the insects on which it feeds because of its 
close resemblance to the leaves around it ; but it is 
also protected in the same manner from the animals 
which prey upon it. Thus Mr. E. A. Minchin tells 
me, from his experience in India, that tree frogs are 
sought for with especial eagerness by snakes, which 
greatly prefer them to others. It is probable that 
this power when possessed by a vertebrate animal 
nearly always bears a double meaning, although a con- 
sideration of the different instances will show that it 
is especially Protective in some and especially Aggres- 
sive in others. In the next chapter we shall meet 
with a large number of cases briefly alluded to at the 
beginning of this chapter, in which the power is in 
many respects different, and possesses an entirely 
Protective meaning. 




No insect is known to possess the power of rapidly 
adjusting its colour to the tints of its surroundings, 
and it has not long been known that any power of 
adjustment exists. There is still a great deal to be 
done in finding out the extent to which the power is 
present, and in further investigating the physiological 
processes which are involved in its operation. Up to 
the present time the Lepidoptera (butterflies and 
moths) alone have been made the subjects of in- 
quiry, and we know nothing of other insects in this 

Many caterpillars and chrysalides have been proved 
to be capable of adjusting their colours to those of the 
surroundings, and it is also known that certain cater- 
pillars can construct cocoons of different colours, so 
as to harmonise with the environment. The latter 
extremely interesting example of Variable Protective 
Resemblance has been very insufficiently investigated. 
It is also probable that a relatively small number of per- 
fect insects possess the same power ; but in this case 


no experimental researches have been conducted. I 
will first consider the chrysalides, because they were 
first found to possess the power, and because it has 
been more completely investigated in them than in 
the other cases. 

Variable Protective Eesemoiance in Lepidopterous Pupae. 

The capability of adjusting the colour to that 
of the surroundings is only present in exposed chry- 
salides, and has not been found hitherto among 
the pupae of Heterocera (or moths), nearly all of 
which are either buried in the earth or concealed in 
opaque cocoons. In both cases the chrysalides are 
generally reddish-brown hi colour, the shade varying 
greatly in different species. The dark colour is of pro- 

FIG. 23. The pupa of Swallow- FIG. 24. The pupa of Swallow- 
tailed Moth, showing colour tailed Moth (Uropteryx sambu- 
assuined when the larva has caia) ; the usual dark colour 
been placed on white paper assumed in cocoon ; natural 
before pupation. size. 

tective value when the chrysalis is accidentally ex- 
posed upon the surface of the earth. 

Since this last paragraph was written, I have 
found that the chrysalis of the Swallow-tailed Moth 


(Uropteryx samlwcata) becomes light-coloured when 
the caterpillar has been placed upon white paper 
shortly before pupation (see fig. 23). The chrysalis 
is usually dark (see fig. 24), and is contained in a 
cocoon which is formed of the brown fragments of 
leaves or twigs spun together with threads of silk. 
The cocoon, which is suspended from the food-plant 
and swings freely, is so loose and open in texture that 
the enclosed pupa is easily seen, and is in fact as 
exposed as that of many butterflies. 

The chrysalides of butterflies are generally freely 
exposed, and many species have been proved to possess 
the power of adjusting the pupal colour to that of 
the adjacent surface. Such pupse are often suspended 
head downwards from a boss of silk, to which the 
hooks at the posterior end are affixed ; or they are fre- 
quently attached horizontally, or in a vertical position 
with the head upwards, by similar posterior hooks and 
a strong silken girdle, which is fixed on either side to 
the supporting surface, and which sinks into a groove 
across the back of the pupa. The group which in- 
cludes the Tortoiseshell and Peacock Butterflies adopts 
the former mode of suspension; that to which the 
* Garden Whites ' belong adopts the latter. 


The History of the Discovery of Variable Protective 
Resemblance in the pupae of Butterflies 

In 1867 Mr. T. W. Wood exhibited to the Entomo- 
logical Society of London l a number of chrysalides of 
the Swallow-tailed Butterfly (Papilio machaori), and of 
the large and small Garden White Butterflies (Pieris 
brassicce and P. rapes), which corresponded in colour to 
the surfaces to which they were attached. Dark 
pupse had been found on tarred fences and in subdued 
light ; light ones on light surfaces ; while green leaves 
were shown to produce green chrysalides, at any rate 
in certain cases. Mr. Wood's inclusion of the chrysalis 
of the Swallow-tail, with which he states that he was 
imperfectly acquainted, was most unfortunate, and 
doubtless prevented his suggestive paper from gaining 
the success it deserved. It is quite true that this 
chrysalis appears in two forms, being sometimes green 
and sometimes dark grey ; but, without sufficient evi- 
dence, it was unwise, although most natural, to assume 
that these colours could be adjusted to green or dark 
surroundings respectively. I have since tested the 
chrysalis, and as far as my experiments (which were 
with small numbers) are conclusive, they show that it 
has no power of adjustment. 2 In the discussion which 
followed Mr. Wood's paper, Mr. Bond stated that ' he 

1 Proc. Ent. Soc. 1867, pp. xcix.-ci. 

Phil. Trans vol. 178 (1887), B. p. 406-408. 


had had thousands of pupae of Papilio machaon, and 
had often had the brown variety of pupa on a green 
ground colour, whilst in some seasons he had obtained 
no brown specimens at all.' 

In spite of this unfortunate mistake, Mr. Wood 
adduced quite sufficient evidence concerning the 
Garden Whites to show that the subject was worth 
investigation. But the great example and the great 
principles of Darwin had not penetrated far into the 
mass of naturalists ; and distinguished entomologists 
preferred the expression of an adverse opinion, to 
making an easy experiment upon one of our commonest 

Mr. Wood also stated that the chrysalis of the 
Large Tortoiseshell Butterfly (Vanessa polychloros) was 
coloured like a withered elm-leaf, when suspended 
among the foliage of the elm on which its caterpillar 
feeds. Its colour was then light reddish-brown with a 
cluster of metallic silvery spots, but when suspended 
from a wall, the metallic spots were not produced, 
and the pupa was of a mottled greyish colour. This 
observation led Mr. Wood to conclude ' that by the 
proper use of gilded surfaces the gilded chrysalides of 
Vanessa, and perhaps of other genera, would be ob- 
tained ' ; and he added, ' I hope to be able to try the 
experiment next season.' If this intention had been 
carried out, such startling results would have been 
obtained that opposition would have broken down 
before them, and the combined researches of many 


naturalists would have been brought to bear upon the 
subject. The experiment, however, was not made till 
nineteen years later, when I was led to do as Mr. 
Wood had proposed, although unaware at the time of 
his suggestion. 

Nevertheless, during these nineteen years, gradual 
confirmation of Mr. Wood's central position was 
afforded. In 1873 Professor Meldola supported the 
observations upon the chrysalides of the ' Garden 
Whites.' He compared large 
numbers of individuals, and 
found that the pupse upon 
black fences were darker 
than those upon walls. 1 

In 1874 a paper by Mrs. 
M. E. Barber, and commu- 
nicated by Mr. Darwin to 
the Entomological Society 
of London, was printed in 
the Transactions of that 
society. 2 'Mrs. Barber had 
experimented with a com- 
mon South African Swallow- 
tailed Butterfly (Papilio 
nireus), and had found the 
chrysalis wonderfully sensi- 
tive to the colours of its environment. When the 
pupae were attached among the deep green leaves of 

1 Zool. Soc. Proc. 1873, p. 153. 2 1874, p. 519. 

FIG. 25. The pnpa of Papttio nireus 
attached to orange tree ; natural 



the food-plant, Orange, they were of a similar colour 
(see fig. 25) ; when fixed to dead branches covered 
with withered, pale yellowish-green leaves, they re- 
sembled the latter (see fig. 26). One of the cater- 
pillars ' affixed itself to the wooden frame of the case, 

FIG. 26. The pupa of PapHio niretu 
attached to plant (Veprii lanceo- 
lata) with withered yellowish-green 

7. The pupa of Papilio nireus 
attached to woodwork. 

and then became a yellowish pupa of the same colour 
as the wooden frame' (see fig. 27). The case was 
made partly of purplish-brown brick and partly of 
wood, and one of the pupae, attached close to the 
junction, was believed by Mrs. Barber to have assumed 


both colours, that of the brick upon its back and that 
of the wood upon its under surface. My experiments 
upon the chrysalis of the Small Tortoiseshell Butterfly, 
to be described below, do not support this conclusion, 
and it is a common thing for the colours of pupae to 
differ greatly in the dorsal and ventral regions. Mrs. 
Barber also tried the effect of scarlet cloth, but little 
if any influence was exerted. 

Mr. Mansel Weale also showed that the colour of 
certain other South African pupae can be modified, 1 
and Mr. Roland Trimen made some experiments 
upon another African Swallow-tail 2 (Papilio demoleus, 
common at Cape Town), confirmatory of Mrs. Barber's 
observations. He covered the sides of the cage with 
bands of many colours, and found that green, yellow, 
and reddish-brown tints were resembled by the pupae, 
while black made them rather darker. Bright red 
and blue had no effect. The larvae did not exercise 
any choice, but fixed themselves indiscriminately to 
colours which their pupae could resemble and those 
which they could not. In the natural condition the 
latter would not exist, for the pupae can imitate all 
the colours of their normal environments. 

Finally, Fritz Miiller experimented upon a South 
American Swallow-tail (Papilio poly damns)? and found 

Trans. Ent. Soc. Land. 1877, pp. 271, 275. 
2 Described in a letter to me, published in my paper already 
referred to, p. 316. 

* Eosmos, vol. 12, p. 448. 


that its pupae, although appearing in two forms, dark 
and green, like those of our own Swallow-tail, also 
resemble the latter in having no power of adjusting 
their colours to the surroundings. 

Theories as to the manner in which the colours of such 
pupae are determined 

These observations and experiments had been 
made when I began to work at the subject in 1886 : 
they appeared to prove that the power certainly exists, 
but nothing was really known as to the manner in 
which the adjustment is effected. Mr. T. W. Wood's 
original suggestion, that 'the skin of the pupa is 
photographically sensitive for a few hours only after 
the caterpillar's skin has been shed,' was accepted 
by most of those who had worked at the subject. 
And yet the suggestion rested upon no shadow of 
proof ; it depended upon a tempting but overstrained 
analogy to the darkening of the sensitive photographic 
plate under the action of light. But the analogy 
was unreal, for, as Professor Meldola stated in the 
discussion which followed Mrs. Barber's paper, ' the 
action of light upon the sensitive skin of a pupa 
has no analogy with its action on any known photo- 
graphic chemical. No known substance retains per- 
manently the colour reflected on it by adjacent 
objects.' The supposed ' photographic sensitiveness ' 
of chrysalides was one of those deceptively feasible sug- 


gestions which are not tested because of their apparent 
probability. It would have been very easy to transfer 
a freshly formed pupa from one colour to another 
which is known to produce an opposite effect upon it ; 
and yet if this simple experiment had been made the 
theory would have collapsed, for the pupa would have 
been found to resemble the first colour and not the 
second. Furthermore, Mr. Wood's suggestion raised 
the difficulty that chrysalides which had become ex- 
posed in the course of a dark night would have no 
opportunity of resembling the surrounding surfaces, 
for the pupal colours deepen very quickly into their 
permanent condition. In working at the subject I 
determined to pay especial attention to such ques- 

Experiments upon the chrysalis of the Peacock 

I began work with the common Peacock Butterfly 
(Vanessa lo), of which the chrysalis appears in two 
forms, being commonly dark grey (see fig. 28), but 
more rarely, bright yellowish-green (see fig. 29) : both 
forms are gilded, especially the latter. The gilding 
cannot be represented in the woodcuts. Only six 
caterpillars could be obtained, and these were placed 
in glass cylinders surrounded by yellowish-green 
tissue paper. Five of them became chrysalides of the 
corresponding colour; the sixth was removed imme- 
diately after the caterpillar skin had been thrown 


off, and was placed in a dark box lined with black 
paper, but it subsequently deepened into a green 

PIG. 28. The pupa of Peacock FIG. 29. The pupa of Peacock 

Butterfly ; dark form ; natural Butterfly ; light yellowish-green 

size. form. 

pupa exactly like the others. Obviously the sur- 
roundings had exercised their influence before the 
pupa was removed. 

Experiments upon the chrysalis of the Small Tortoise- 
shell Butterfly 

Being unable to obtain more larvae of the Peacock, 
I worked upon the allied Small Tortoiseshell Butterfly 
(Vanessa urticce), which can be obtained in immense 
numbers. In the experiments conducted in 1886, 
over 700 chrysalides of this species were obtained and 
their colours recorded. Green surroundings were 
first employed in the hope that a green form of pupa, 
unknown in the natural state, might be obtained. 
The results were, however, highly irregular, and there 
seemed to be no susceptibility to the colour. The pupas 
were, however, somewhat darker than usual, and this 


result suggested a trial of black surroundings, from 
which the strongest effects were at once witnessed : 
the pupae were as a rule extremely dark, with only 
the smallest trace, and often no trace at all, of the 
golden spots which are so conspicuous in the lighter 
forms. These results suggested the use of white sur- 
roundings, which appeared likely to produce the most 
opposite effects. The colours of nearly 150 chrysalides 
obtained under such conditions were very surprising. 
Not only was the black colouring matter as a rule 
absent, so that the pupae were light-coloured, but 
there was often an immense development of the 
golden spots, so that in many cases the whole surface 
of the pupae glittered with an apparent metallic lustre. 
So remarkable was the appearance that a physicist, to 
whom I showed the chrysalides, suggested that I had 
played him a trick and had covered them with gold-leaf. 

These remarkable results led to the use of a gilt 
background as even more likely to produce and in- 
tensify the glittering appearance. By this reasoning 
I was led to make the experiment which had been 
suggested by Mr. Wood nineteen years before. The 
results quite justified the reasoning, for a much higher 
percentage of gilded chrysalides, and still more remark- 
able individual instances, were obtained among the 
pupae which were treated in this way. 

The following table shows the results of some ex- 
periments in which the above-mentioned colours were 
employed : 



















Degrees of colour 




- g -Si 

^ g- 


s ? 

I js"S 






















g uw 



Green surroundings 








= 3 

= 105 








= 145 








- 67 


In order to realise these results it must be remembered 
that the appearance represented by (4) or (5) is very 
rarely seen in nature, except when the pupa is dis- 
eased. By far the commonest varieties met with are 
those represented by (3), which are therefore called 
normal forms. 

Special advantages of the Small Tortoiseshell for 
purposes of experiment 

From the results expressed in the tabular form 
given above, it was clear that this species was very 
susceptible to surrounding colours, and that black 
and gold produced the most opposite effects. Another 
advantage in the use of this species is the fact that 
the caterpillars live in companies, each of which 


develops from the eggs laid by a single butterfly. 
Hence by keeping the companies separate, the varying 
hereditary tendencies, due to different parentage, are 
eliminated ; for a company of moderate size would 
contain over one hundred larvae, and would therefore 
furnish the material for several experiments. Con- 
sidering also the abtuadance of the species, I determined 
to employ it for the investigation of the process by 
which the change of colour is effected. 

The pupae darker when crowded together 

Very early in the investigation a possible source 
of error was detected. It seemed probable, when 
many individuals were collected together at the sus- 
ceptible period, which will be shown to occur towards 
the end of larval life, that each of them would be 
affected by that part of the surroundings which was 
constituted by the black skins of its neighbours. It 
was therefore necessary to take into account the 
relative positions of the pupae, and, in the most 
careful experiments, to place only a single individual 
in each coloured case. Experiment soon showed 
that these precautions were necessary. Many of the 
darker pupae, shown in the table to be produced by 
white and gilt surroundings, were proved to have 
been influenced 'by mutual proximity, so that the 
results would have been even more striking if this 
source of error had been allowed for. 


The period during which the colours of pupae are 

A very large number of experiments and the 
closest and most frequent observations were devoted 
to the determination of the time during which these 
organisms are sensitive to surrounding colours. It 
was first necessary to observe everything that happens 
to a caterpillar between the cessation of feeding and 
the change into a chrysalis, for I felt sure that the 
time of susceptibility lay somewhere within these 
limits. When one of these caterpillars is full-fed, 
it descends from its food-plant (nettle) and wanders 
about in search of some suitable surface upon which 
to pass the pupal period. This is stage i., and its 
length varies greatly, according to the proximity of 
suitable surfaces. Then the caterpillar, having found 
the surface, rests motionless upon it, generally in a 
somewhat curved position. This is stage ii., and it 
is also variable in length, but fifteen hours may be 
accepted as a fair average of the time spent in this 
position. Finally the caterpillar hangs, head down- 
wards, suspended by its last pair of claspers (larval 
legs), which are attached to a boss of silk spun at the 
close of the second stage. This is stage iii., which 
lasts for about eighteen hours, at the end of which 
time the skin splits along the back behind the head, 
and the chrysalis is exposed by the skin being worked 


up towards the boss of silk. Then the tail of the 
chrysalis is withdrawn from the interior of the skin 
and is forced up the outside of the latter, until it 
comes in contact with the boss of silk. Contact 
immediately causes some of the numerous hooks on 
the end of the chrysalis to be entangled in the silk. 
During this apparently perilous operation the chrysa- 
lis is suspended to the larval skin, although different 
opinions obtain as to the exact method of its attach- 
ment. The sight is extremely interesting and beautiful, 
and the operation is almost always performed with 
precision and success. As soon as the pupa is firmly 
attached to the silk, it endeavours, by the most violent 
movements, to get rid of the skin, and generally 
succeeds in detaching it. 

Exact determination of the period of susceptibility 

The whole of the period before pupation, including 
the three stages, may be estimated at about thirty-six 
hours. Even if the caterpillars were susceptible 
during stage i., no effective results could be obtained ; 
for they are then wandering over surfaces of various 
colours, of which few can be the same as that which 
will form the environment of the chrysalis. Many 
experiments were conducted with the object of as- 
certaining the exact period of susceptibility. Larvae 
were exposed to one colour during stages i. and ii., 
and then transferred to another colour for stage iii., 



while other larvse were exposed to each of the colours 
for all three stages : the effects were then compared. 
The results of the largest experiment of the kind are 
given below : 


Degrees of colour 




(as before) (1) 






( 6 ) 


In black surroundings for all 

three stages . . . 




= 7 

Transferred from black into 

gilt for stage iii. . . 




= 9 

Transferred from gilt into 

black for stage iii. . . 



= 15 

In gilt surroundings for all 

three stages . . . 




= 20 



This analysis speaks for itself. Stages ii. and iii. are 
both sensitive, but stage iii. is much less sensitive 
than the other. This is proved by the fact that the 
larvae which had been exposed to gilt surroundings 
during stage ii. and to black afterwards, were lighter 
thm those which had been exposed to black during 
stage ii. and to gilt afterwards. In other words, the 
coloured surroundings, both gilt and black, produced 
more effect during stage ii. than iii. ; but both stages 
are sensitive, because the black and gilt surroundings 
produced still greater effects when they operated for 
the whole period before pupation. It must be ob- 
served that the caterpillars, in the experiment sum- 
marised above, tended as a whole to produce the 
lighter forms of chrysalides, so that the black did 


not cause nearly such strong effects as the gilt sur- 
roundings. The tendency was evidently hereditary 
and shared by all the caterpillars of the company, so 
that we have a striking example of the errors which 
were eliminated by keeping the companies separate. 

It is almost unnecessary to point out how com- 
pletely the old theory of ' photographically sensitive ' 
chrysalides is broken down by these experiments. 
Not only is the adjustment of the pupal colours to 
their surroundings due to larval susceptibility, but 
the larva itself has ceased to be highly sensitive many 
hours before pupation takes place. And this is to be 
expected, for during the latter part of stage iii. rapid 
changes are going on beneath its surface, and the 
developing pupa is becoming loosened from the larval 
skin which encloses it like a shell. Putting together 
the results of all the experiments, it is probable that 
in this species the influence of surrounding colours 
operates upon the larva during the twenty hours 
immediately preceding the last twelve hours of the 
larval state. Hence stage ii. is the great period of 
susceptibility, and this is probably the true meaning 
of the hours during which the caterpillar rests motion- 
less on the surface upon which it will pupate ; while 
stage iii. has other meanings connected with the rapid 
pupal development which is taking place. 


Determination of the part affected by surrounding 

Having thus defined the time of susceptibility, the 
next question was to ascertain the organ or part of 
the larva which is sensitive. At first it appeared 
likely that the larvae might be influenced through their 
eyes (ocelli), of which they have six on each side of the 
head. Hence in many experiments the eyes of some 
of the larvae were covered with an innocuous opaque 
black varnish, and they, together with an equal number 
of normal larvae from the same company, were placed 
in gilt or white surroundings. The pupae from both 
sets of larvae were, however, always equally light- 
coloured. It then seemed possible, although highly 
improbable, that the varnish itself might act as a 
stimulus similar to that caused by white or gilt 
surroundings, and therefore the experiment was re- 
peated with black surroundings in darkness ; but the 
pupae of the two sets were again almost identical, so 
that it appeared certain that the eyes can have 
nothing to do with the influence. 

It then seemed possible that the large branching 
bristles, with which the larvae are covered, might con- 
tain some organ which was affected by surround- 
ing colours, but experiments in which half of the 
larvae were deprived of their bristles showed con- 
clusively that the sensitive organs must have some 


other position, for the pupse from both sets of larvae 
were identical. 

I was thus driven to the conclusion that the 
general surface of the skin of the caterpillar is sensi- 
tive to colour during stage ii. and part of stage iii. 
In order to test this conclusion I wished to subject 
the body of the same larva to two conflicting colours, 
such as black and gold, producing the most opposite 
effects upon the pupa. Such an experiment, if 
successfully carried out, would decide some important 
points. If the part of the body containing the head 
was not more sensitive than the other part, a valuable 
confirmation of the blinding experiments would be 
afforded. Mrs. Barber's suggestion that parti- coloured 
pupae may be produced by the influence of two colours 
would be tested in a very complete manner ; if parti- 
coloured pupae were obtained it seemed probable that 
the light acts directly upon the skin, but if they could 
not be obtained it seemed more probable that the 
light influences the termination of nerves in the skin, 
and that the pupal colours are produced through the 
medium of the nervous system. 

The practical difficulties in the way of such an ex- 
periment were very great, for the conflicting colours 
could only be applied during stage iii., when the larva 
is motionless and may be disturbed with impunity. 
If, on the other hand, a larva be disturbed in stage 
ii. it begins to walk about and thus renders the 
experiment impossible. The only way to obtain 


satisfactory results in spite of the slight susceptibility 
of stage iii. was to employ large numbers of larvaa, 
and to pay careful attention to minute differences of 
pupal colour as well as to the time during which the 
conflicting colours had been applied. 

The experiments were conducted in two ways. 
In the first the larvae were induced to suspend them- 
selves from sheets of clear glass, by placing them in 
wide shallow glass boxes so that the ascent to the 
glass roof was easily accomplished.. As soon as sus- 
pension (stage iii.) had taken place, each larva was 
covered with a cardboard tube divided into two 
chambers by a horizontal partition which was fixed 
rather below the middle. There was a central hole 
in the partition just large enough to admit the body 
of the larva. The tube was fixed to the glass sheet 
with glue; the upper chamber was lined with one 
colour, e.g. gilt, and the lower chamber with the 
opposite colour, e.g. black, with which the outside of 
the cylinder was also covered, in case the larva should 
stretch its head beyond the lower edge. The parti- 
tion was fixed at such a height that the larval head 
and rather less than half of the total surface of skin 
were contained in the lower chamber, while rather 
more than half of the skin surface was contained in 
the upper chamber. The arrangement is shown in 
section in fig. 30. 

The second method of conducting the conflicting 
colour experiments was superior in the more equal illu- 


mination of the upper and lower colours. The bottom 
of a shallow wooden box was covered with alternate 
areas of black and gilt paper, and partitions were 
fixed along the lines where the two colours came into 
contact. Each par- 
tition was gilt to- 
wards the gilt surface 
and black towards 
the black, and was c 
perforated close to 
the bottom of the 
box with holes which 
would just admit the 
body of a larva. The 
box was then placed 
in a vertical position 
towards a strong 
light, so that the 
partitions became 

horizontal shelves, while the black and the gilt sur- 
faces were uppermost alternately. As soon as a larva 
was suspended to a glass sheet, the boss of silk was 
carefully scraped off and was pinned on the upper colour 
above one of the holes, so that the head and first five 
body-rings passed through the hole on to the colour 
beneath, which tended to produce opposite effects. 
Other larvae were similarly fixed between the shelves 
upon one colour only, so as to afford a comparison 
with the results of the conflicting colours. 

FIG. 30. The larva of Small Tortoiseshell Butter- 
fly suspended in a tube of which the upper 
compartment is lined with gilt, the lower with 
black ; x 2. s. Boss of silk. b. Black, c. Card- 
board, g. Gilt. 


A careful comparison of all the pupse obtained in 
the conflicting colour experiments showed that, when 
the illumination of the two surfaces was equal, the 
effective results were produced by that colour to 
which the larger area of skin had been exposed, 
whether the head formed part of that area or not. 
Parti-coloured pupae were never obtained. It there- 
fore appears to be certain that the skin of the larva 
is influenced by surrounding colours during the sensi- 
tive period, and it is also probable that the effects are 
wrought through the medium of the nervous system. 
This latter conclusion receives further confirmation 
from other observations which will be described in the 
next chapter (see pp. 142- ^1G). 


INSECTS (continued) 

The meaning of the metallic appearance of pupae 

APART from the general physiological significance of 
the results described in the last chapter, they are of 
extreme interest in giving us a possible clue to the 
meaning of the remarkable metallic appearance of 
the pupae of many butterflies. This wonderful appear- 
ance has given the name chrysalis to the second 
stage of Lepidopterous metamorphosis, although rela- 
tively few pupae are really entitled to bear it. But 
some pupae which deserve the name are very common, 
and probably have attracted attention ever since men 
began to look with interest on the world around them. 
Not only did the alchemists believe that in the appear- 
ance of these animals they received encouragement 
for the successful issue of the projects which were 
always before them, but we find that Aristotle, writing 
more than 2,200 years ago, mentions chrysalis as a 
word which was generally used * in his time, and which 
had therefore been invented as descriptive of the 


golden appearance at a still earlier period. There can 
be no doubt of this, for Aristotle's word is xpva-a\\is, 
identical with our own ; nor can there be any doubt 
as to the stage of insect life to which Aristotle was refer- 
ring, for his language is precise and descriptive. In 
fact, if a naturalist wished to convey to any one igno- 
rant of the changes undergone in insect metamorphosis 
a short and simple but perfectly accurate account of 
the two first stages of a Lepidopterous insect, he could 
not do better than use the very words of Aristotle : 
' Caterpillars take food at first, but afterwards they 
cease to take it and become quiescent, being generally 
called chrysalides ; ' ! or again in another passage : 
'Afterwards the caterpillars, having grown, become 
quiescent, change their shape, and are called chrysa- 
lides.' 3 

Mr. T. W. Wood suggested that the metallic 
appearance was so essentially unlike anything usually 
found in the organic kingdoms, that it acted as a 
protection to the organisms possessing it. Others 
have thought that it has the value of a warning 
colour, indicating an unpleasant taste (see Chapter 
X.). It is probable that the appearance sometimes 
bears this meaning now, but it is unlikely that such 
was its original use ; for the fact that metallic colours 
can be called up or dismissed by the appropriate sur- 

1 o? re yap \afi.&avovffi rii vpurov Tptxpfyv, yueri ravra ovKtrt 

i', d\A.' aKivtiTi^ovfflv al KaAov/j.ei/ai \nr& Tivtav xpWAAfSes. 
iiero 5 -ravra (at] av|7j0i<rat a.Kwriri^oL.(ri > ical 
T^V (iop<t>1)v, ical KaXovvrai 


roundings shows that they are essentially protective, 
and as far removed as possible from conspicuous 
warning colours, the object of which is to render their 
possessors unlike the environment. What can be the 
object in nature which the glittering pupae resemble ? 
It is obvious that metals are not sufficiently abun- 
dant on the surface of the earth to afford models for 
successful imitation, and there is the same objection 
to certain metallic sulphides which otherwise would 
answer the purpose admirably. 

A consideration of the darker non-glittering va- 
rieties of the same species helps us to an explana- 
tion. These certainly resemble the grey surface of 
weathered rocks, and the whole shape of such pupae, 
with their angular projections and tubercles, com- 
bines with their colour to produce a most perfect 
Protective Kesemblance to rough dark surfaces of 
rock. In fact, did we not delude the larvae by offering 
them flat mineral surfaces in our walls and sides of 
houses, the protection would be so complete that 
we should hardly ever find the chrysalides ; and, as 
a matter of fact, they are rarely seen except in such 

In England we very rarely see a brightly metallic 
pupa because in our moist climate exposed rock- 
surfaces quickly weather and become lichen-covered. 
If, however, the bright appearance of many recently 
fractured rocks were retained, as they are in drier 
countries, they would cause the production of a similar 


appearance in the pupae of those larvae which sought 

Although metallic surfaces are not conspicuous in 
nature, there is a very abundant glittering mineral 
which is quite common enough to offer a surface 
against which the larvae might often suspend them- 
selves. I refer to the mineral mica, the substance 
forming the glittering flakes which are so well-known 
in common granite. Furthermore, any recently 
broken rock contains bright and glittering surfaces, 
although they may not be so brilliant as mica, and 
the bright spots of the pupae would thus be of pro- 
tective value against almost any freshly exposed 
mineral surface. 

Hence we see that the pupae would occur as dark 
or glittering forms, as the surrounding mineral sur- 
faces are dark or glittering : they appear in two 
different varieties which are respectively in harmony 
with the two conditions of the mineral surfaces they 
resemble the dark and weathered, and the bright 
and freshly exposed condition. 

It may be that this adaptation to mineral sur- 
roundings arose when the widespread green tints of 
the vegetable kingdom contributed less to the total 
appearance of land-surfaces ; or the adaptation may 
have followed the habit of feeding upon herbaceous 
plants which withered away in the hot season, 
changing from green to brown during the time when 
the insect was in the chrysalis state and could 


undergo no corresponding change of colour. How- 
ever the adaptation arose in the ancestor of all butter- 
flies which now emerge- from gilded chrysalides, it is 
probable that it took place in some hot dry country, 
where mineral surfaces did not weather quickly but 
remained glittering for long periods of time. 

The manner in which golden chrysalides are adapted 
for concealment on plants 

In the origin and gradual progress of our modern 
aggressive forms of vegetation, less and less of the 
land-surface has been formed by mineral substances, 
until the green colour of foliage and the brown colour 
of stems and of withered leaves have become the pre- 
dominant tints of nature and the most feasible models 
for Protective Eesemblance. It is therefore interesting 
to note how the species with gilded pupse have adapted 
themselves to the change. 

The chrysalis of the Peacock Butterfly (Vanessa lo) 
still retains the dark variety, which is formed when 
pupation takes place upon dark rock surfaces ; but the 
golden form has been replaced by a green variety, 
which is produced when the chrysalis is suspended 
from the leaves of its food-plant. The green variety 
still retains the metallic appearance, and exhibits it 
to a much greater extent than the dark variety. 
During the summer of 1888 I found that the green 
form is produced by the surroundings which cause 


the appearance of the gilded form of the Small 
Tortoiseshell chrysalis, viz. by a gilt and by a white 

The chrysalis of the Eed Admiral Butterfly 
(Vanessa Atalanta) has no green variety, but it appears, 
like the Small Tortoiseshell, as a dark or a glittering 
form resembling the two conditions of rock-surfaces 
upon which it often pupates, hanging suspended 
without any attempt at concealment except such as is 
afforded by its very perfect colour-harmony with the 
surroundings. I have shown that this species also is 
susceptible, and that either variety of pupa is produced 
by the appropriate environment. But this chrysalis 
is very commonly found attached to the food-plant, 
and when this is the case it hangs suspended in a 
tent formed of leaves carefully spun together by the 
caterpillar, so that it is concealed from view. The 
larva also often has the habit of partially biting 
through the leaf-stalk or stem, so that the leaves of 
its retreat hang down and wither. The dead brown 
leaver thus afford a far more harmonious background 
for the dark pupa, if by any chance it becomes 
exposed to view. 

The Small Tortoiseshell has neither the green 
variety of the Peacock nor the protective habit of 
the Eed Admiral, and therefore it almost invariably 
seeks mineral surroundings for the pupal period, and 
very rarely becomes a chrysalis on its food-plant. 
In 1886 I only found three such pupse suspended to 


the food-plant, although I examined the nettle-beds 
where many hundreds of caterpillars had been feeding 
and had left for pupation. All these three pupae were 
dead, being filled with the parasitic larvae of Ichneumon 
flies. In 1888 I found many more pupae upon the 
food-plant, but a very high percentage of these had 
been killed by parasites, and the hurrying on of 
pupation which occurred in the other cases and pre- 
vented the larvae from wandering in a normal manner 
may, I think, be attributed to the state of health 
induced by that extraordinarily wet season. 

The colours of certain dimorphic pupae cannot be adjusted 
to the surroundings 

I have already mentioned that I experimented 
upon the pupae of the Swallow-tailed Butterfly 
(Papilio machaori), and found that they were not sus- 
ceptible to the influence of surrounding colours. This 
is also true of the small family of Mocha moths 
(Ephyrida) which have freely exposed pupae, fixed 
like those of many butterflies by a silken girdle and 
boss, and often appearing in two varieties, green and 
brown. The caterpillars of the same species are also 
of two colours, and always produce pupae of corre- 
sponding tints (see page 46). 


Variable Protective Resemblance in the pupae of the 

The susceptibility of the two species of Garden 
White Butterflies (Pieris brassica and P. rapes) was 
also investigated in the same season (1886), and the 
results of previous observers were confirmed and 
extended. Many colours were employed, and it was 
found that the light reflected from yellow and orange 
surroundings was very potent in producing bright 
green varieties of the chrysalides of both species. It 
is therefore probable that when the light reflected 
from green leaves produces this effect in nature, the 
yellow and orange constituents of the light form 
the stimuli. When, therefore, these constituents are 
made use of nearly alone, they produce still more 
marked effects. Black and white backgrounds caused 
the pupae of both species to become dark and light 
respectively, and all other colours except yellow and 
orange produced more or less dark pupae. 

Experiments were made upon P. rapce, to ascertain 
the susceptible period, the larvae being transferred as 
in the case of the Small Tortoiseshell. The results 
were as in the latter : the larva is sensitive and not 
the pupa, and the time of chief susceptibility is during 
stage ii. 

A few larvae of P. rapce were blinded, but the chry- 
salides were similar to those produced by normal larvae. 


Further experiments on the same subject 

During the summer of 1888 I conducted further 
experiments upon the same subject. The results are 
as yet imperfectly worked out, and are unpublished, 
but I will shortly mention the chief conclusions. 
Other glittering metallic surfaces, such as silver or tin, 
do not produce anything like so striking an effect as 
gold upon the pupaB of the Small Tortoiseshell. It 
seems probable that the yellow light reflected from 
the gold is effective in preventing the formation of 
pigment, and in thus producing the gilded chrysalides, 
just as the yellow light also prevents the appearance 
of pigment and produces the bright green pupae among 
the Pierida. 

Two new species also were investigated, and proved 
to be sensitive. The pupae of the Silver-washed 
Fritillary (Argynnis paphia) can be rendered dark or 
light in colour, although the metallic spots do not 
seem to be affected. The pupae of the Large Tortoise- 
shell (Vanessa polycTiloros) were also rendered dark 
brown without metallic spots, or light reddish-brown 
with the spots, by the use of appropriate surroundings. 
The metallic spots could not be extended over the 
pupal surface as in the case of the Small Tortoise- 


Confirmatory results obtained by other workers 

It is also interesting to record that many of these 
results have been since confirmed by independent 
workers. Mr. G. C. Griffiths worked at the chrysalis 
of the Small Garden White (Pieris rapce), and con- 
firmed my results in many important respects. 1 The 
Eev. J. W. B. Bell and Mr. Pembrey have worked at 
the pupae of the Small Tortoiseshell and Peacock, and 
the former also at the pupse of the Large Tortoise- 
shell. 2 Their results are, on the whole, confirmatory 
of those described above. 

Variable Protective Resemblance in the colours 
of cocoons 

It has been already mentioned that the colour of 
the cocoon in certain species can be adjusted to the 
environment. I obtained proof of this in 1886, at 
the suggestion of Mr. W. H. Harwood of Colchester, 
who had observed that the colour of the cocoon of the 
Emperor Moth (Saturnia carpini) varied, and seemed 
to suit its environment. I found that caterpillars of 
this species spun very dark brown cocoons in a black 
calico bag (see fig. 31), while white cocoons were 

Trans. Ent. Soc. Lond. 1888, pp. 247 et seq. 
The Midland Naturalist, Dec. 1889, pp. 289-90. 


spun in white surroundings in a strong light (see 
fig. 82). 

In this case it seems almost impossible for the 
surrounding colours to influence directly the colour of 
the cocoon. It is necessary to assume the existence 

FIG. 31. The cocoon of Emperor Moth PIG. 32. The cocoon of Emperor Moth, 

(S. carpini), spun in a black calico spun on a white surface in strong 

bag ; natural size, although an excep- light ; natural size, 
tionally small cocoon. 

of a complex nervous circle as a medium through 
which the stimulus of colour can make itself felt. If 
this conclusion be correct it is probable that the 
colours of the pupa and larva are adjusted in the 
same manner. 

The observation upon S. carpini has been con- 

1 Proc. Hoy. Soc. vol. xlii. p. 108. I have since found that the 
fact must have been known previously, for it is quoted in Mr. A. R. 
Wallace's Tropical Nature. I do not yet know the name of the 
naturalist who made the observation. 


firmed, and has been extended to other species. Thus 
Kev. W. J. H. Newman showed that the cocoons of the 
Small Eggar Moth (Eriogaster lanestris) are creamy 
white when spun upon white paper (see fig. 33) , dark 

FIG. 33. The cocoon of Small Eggar PIG. 34. The cocoon of Small Eggar 
Moth (E. lanestris), spun upon white spun among green leaves, 

paper ; natural size. 

brown when constructed among leaves (see fig. 34) - 1 
These cocoons are so compact and smooth that they re- 
semble birds' eggs : a fact which explains the name of 
the moth. In constructing the cocoon the caterpillar 
leaves a few holes, which are doubtless of importance 
in permitting a free exchange of air. The fact that 
light reflected from green leaves is here the stimulus 
for the production of a dark colour is readily intelligible 
when we remember that the moth does not emerge till 
the following February at the earliest, while the in- 
sect often remains in the pupal state for one or two 
years longer. The leaves in contact with the cocoon 
soon die and turn brown, and after this change the 
dark colour is highly protective. It is also of especial 
importance for the cocoon to be well concealed during 
the winter months, when insect-eating animals are 

1 /Yoc. Ent. Soc. Land. 1887, pp. 1. li. 


pressed for food, and are obliged to search for it with 
extreme care. 

I have also shown that the cocoon of the Green 
Silver Lines Moth (Halias prasinand) can be modified in 
colour like that of the Small Eggar. 1 This species also 
passes the winter in the chrysalis state, when the brown 
colour is highly protective. One of my caterpillars 
had begun to spin a brown cocoon upon an oak leaf 
(see fig. 35). I then removed the caterpillar to a white 
box ; it remained motionless for several hours and then 

FIG. 36. White cocoon spun by same 
caterpillar when transferred from 
oak leaf to white paper; natural 

Fio. 35. Brown oocoon begun 
by caterpillar of Green Silver 
lines Moth (fi.prasinana)\ifOQ 
an oak leaf ; natural size. 

FIG. 37, The brown oocoon of 
Green Silver Lines spun upon 
an oak leaf. 

spun a white cocoon (see fig. 36). The brown cocoon 
of the same species is shown in fig. 37. Remembering 
the experiments upon the Small Tortoiseshell, it is 
very probable that the colour of the cocoon was deter- 

Proc. Ent. Soc. Lond. 1887, pp. 1. li. 


mined during the time when the caterpillar was 
motionless in the box. 

Still later in 1888 Dr. E. G. Lynam sent me some 
cocoons of the Gold-tail Moth (Liparis auriflua) which 
had been also modified in a similar manner, and I 
found that the same power is possessed by the cater- 
pillar of the Brimstone Moth (Rumia crat&gatd) . l In 
this latter case a green tissue-paper background pro- 
duced brown cocoons like those spun upon green leaves. 

It is probable that this power of adjusting the 
colour of the cocoon is very common among species 
which spin in exposed situations. It may also be 
expected to occur in those Hymenoptera with similar 
habits. The investigation of the physiological pro- 
cesses involved in the adjustment would be of extreme 
interest. Last year (1888) I obtained a large number 
of Small Eggar caterpillars, intending to begin such 
an investigation, but nearly all of them died just 
before reaching maturity. It is to be hoped that 
many species will now be tested in order to ascertain 
whether this form of susceptibility is present. 

Variable Protective Resemblance in Lepidopterous 

It now remains to briefly consider the power of 
colour-adjustment possessed by certain caterpillars. 
Naturalists have long known that in certain species 
1 Proc. Ent. Soc. Land. 1888, p. xxviii. 


the colour of the caterpillars may vary according to 
the colour of the plant upon which they are found. 
This is especially true of caterpillars feeding upon 
brightly coloured parts of the plant, such as the 
anthers or petals. At the same time there has been, 
until recent years, hardly any systematic investigation 
of these interesting facts. Professor E. Meldola's 
editorial notes to his translation of Dr. Weismann's 
' Studies in the Theory of Descent ' (the essay on 
' The Origin of the Markings of Caterpillars ') contain 
many instances of this kind, together with most sug- 
gestive remarks upon them, which first induced me to 
work at the subject. At a still earlier date the same 
writer had brought together all the scattered examples 
of this kind, including the power of adjusting the 
colours of pupae, and had drawn attention to the 
general principles involved. 1 

Experiments upon the larva of the Eyed Hawk Moth 

(Smerinthus ocellatus) 

The instance which Professor Meldola chiefly con- 
siders in his editorial notes is that of the caterpillar 
of the Eyed Hawk Moth (Smerinthus ocellatus), which 
is of a whitish-green colour when it is found upon 
apple and certain kinds of willow, and of a bright 
yellowish-green when found upon other species or 
varieties of willow. ' The colours are on the whole 

1 Proc. Zool. Soc. 1873, p. 153. 


protective; the larva resembles the under side of a 
rolled- up leaf, and when the food-plant bears leaves 
with white and downy under sides (apple, Salix 
viminalu, &c.) the larva is usually whitish ; while it 
is generally yellowish-green upon trees of which the 
leaves have green under sides (Salix triandra, S. baby- 
lonica, S. rubra, S.fragilis, &c.). I remember, when 
a boy, finding the two varieties of larva, and being 
much astonished at the difference between them. 

I began working at the species in 1884, and have 
bred large numbers of the larvae for every season since 
that year. Only the results of the earlier experiments 
are published. 1 The eggs of each female moth were 
kept separate, and the caterpillars of each batch were 
fed upon a variety of food-plants, and manifested de- 
cided differences in their shade of green. At the same 
time remarkable exceptions occasionally occurred : 
sometimes, also, when collecting I have found bright 
green individuals upon apple. Blinding experiments 
like those upon the Small Tortoiseshell led to negative 
results. These experiments were very laborious, for 
a caterpillar changes its skin four times, and with it 
the covering to its eyes and the opaque varnish. Hence, 
before each change of skin the caterpillars were sepa- 
rated from the food, and, after changing it, were re- 
blinded before being restored. 

Before this investigation had been begun, it waa 
believed that such variability in caterpillars was due to 

1 Proc. Boy. Soc. vol. xxxviii. p. 269 ; vol. xl. p. 135. 


the direct chemical effect of different kinds of leaves 
upon them after being eaten, and it was therefore 
called phytophagic variability. Many special experi- 
ments were directed toward the solution of this 
question. Thus, leaves were sewn together, so that 
the caterpillars were exposed to the colour of the 
upper or of the under side alone, although they ate 
the same leaf in both cases. In other instances the 
' bloom ' was rubbed off the under sides of some leaves 
(Salix fragilis, incorrectly described as Triandra in 
my papers) , while others were left normal. The results 
proved that the caterpillars are affected by the colour 
of the leaves and not by the leaves as food. Com- 
parison with the experiments on pupae renders it 
most probable that reflected light influences the skin. 

Experiments upon the larvae of other Sphingidse 

Professor Meldola had also quoted the instance of 
the larva of the Privet Hawk Moth (Sphinx ligustri), 
which is of a much brighter green when found upon 
privet than when found upon lilac. Larvae of this 
species, from the same batch of eggs, were fed upon 
the two plants, and the above quoted observation 
was confirmed. The larvae of the Lime Hawk Moth 
(Smerinthus tilice) were similarly modified, being made 
unusually light green by the use of variegated elm 
and a lime having leaves with very white and downy 
under sides. 



Experiments upon the larvae of Geometrae and Noctuae 

The experiments were then extended to many 
other dark-coloured larvae (chiefly Geometree). The 
method of experiment was as follows : a larva which 
resembles the twigs or bark of its food-plant was 
selected, and was surrounded by the leaves upon which 
it fed, and by white or green surfaces. No brown 
twig or anything dark-coloured was allowed to come 
near it during its whole life. Under these circum- 
stances the larvae, in the majority of the species selected 
for experiment, became very light brown or light grey 
in colour, and quite unlike the darker larvae of the 
same kinds which were produced when an abundance 
of dark twigs had been mixed with the leaves of the 
food-plant. 1 

The results were certainly protective, for the 
lighter larvas were far less conspicuous en the green 
leaves and stems than the darker ones would have 
been. At the same time it must be admitted that the 
resemblance of the darker forms to the dark branches 

1 These experiments have been successfully applied to the follow- 
ing Gcometrce : Crocallis elinguaria (for two seasons), Ennomos 
angularia, E. htnaria, Boarmia rhomboidaria (this species was inves- 
tigated by my friend and pupil, Mr. E. C. L. Perkins, B.A., of Jesus 
College, Oxford), B. roboraria ; and to one of the Noctuce, Catocala 
sponsa, Since this note was written, I have found, during the past 
summer (1889), that the Geometer Heterophylla abruptaria, and the 
Noctuas Catocala electa and C. elocata, are also sensitive, the first and 
last named to a marked degree. 


is much stronger than that of the light varieties to 
the leaves (see figs. 38 and 39). Two species, how- 
ever, are already known in which the green stems and 

FIG 38. The larva of a continental Noctua (Calocala elocata) with the colour 
adjusted to that of the dark twigs mixed with its food-plant ; nearly full-fed ; 
two-thirds natural size. 

FIG. 39. The colour of a larva of the same species when only preen twigs and leaves 
were supplied to it. The food-plant in both cases was black poplar (Populut 

leaves cause the production of green larvae, so that the 
concealment is very perfect. And we may be quite 
sure tha,t there are many other species with equal 

Experiments upon the larvae of the Brimstone Moth 

Lord Walsingham first pointed out to me that the 
larvse of the Brimstone Moth (Eumia cratcegata) vary 
from brown to green, and through all intermediate 
shades. I found that when brown objects were 



entirely excluded the larvae became greenish-brown, 
brownish-green, or sometimes of a decided green 
colour, and thus harmonised well with the leaves and 
young green twigs of the hawthorn. In the presence 
of dark twigs they became dark brown like so many 
other larvae. 1 

Experiments upon the larvae of the Peppered Moth 

The second instance is even more remarkable, and 
has only been observed during the present year (1889). 
i I obtained some 

hundreds of eggs 
from a single wild 
female of the Pep- 
pered Moth (Am- 
phidasis betularid), 
and the caterpillars 
which hatched were 
treated as in the 
other experiments. 
The larvae reared 
among green leaves 
and shoots became 

FIG. 41. The larva of Peppered Moth surrounded by bright green (866 
abundant dark twigs as well as leaves. 

fig. 40) iciihout ex- 
ception, while the others in nearly all cases assumed 
the colour of the dark-brown twigs, which were mixed 

1 Report of the British Association, 1887, p. 756 ; also Nature, 
vol. 36, p. 594. 

FIG. 40.-The larva of Peppered Moth (A. betularia) 
surrounded by green twigs and leaves ; full-fed ; 
half natural size. 


with the leaves upon which they fed (see fig. 41) : 
about one or two per cent., however, took their colour 
from the latter. The food-plants were the same in 
both experiments. 

The change of colour is not due to the food seen through 
a transparent skin 

Some authorities have supposed that the change 
of colour under such circumstances is a comparatively 
simple thing, that the younger green leaves eaten 
and seen in the alimentary canal through the more or 
less transparent tissues cause a brighter appearance, 
while the older leaves produce in the same manner a 
darker appearance. This cause of colour is certainly 
efficient in many transparent caterpillars (see p. 79), 
such as some of the Noctua, but it does not account 
for any of the results obtained in my experiments. 

As a precaution against such an error, I reversed 
the surroundings of a few larvae of most of the species 
experimented upon. The new conditions were main- 
tained for some days, during which the contents of the 
alimentary canal must have been changed many times, 
but no perceptible effect was produced. This result 
also serves to show that the influences act very slowly, 
and that the processes of adjustment are totally dif- 
ferent from those which cause the rapid changes of 
colour considered in Chapter VII. 


The difference between slow and rapid adjustment 
of colour 

The essential difference between the two kinds of 
adjustment is that, in the one case, the pigmented 
part of certain cells contracts in obedience to nervous 
stimuli, and thus alters the general appearance ; while 
in the other case the coloured part is actually built 
up of the appropriate tint, or loses its colour alto- 
gether and becomes transparent in obedience to the 
same stimuli. The frog or fish has a series of ready- 
made screens which can be shifted to suit the environ- 
ment ; the insect has the power of building up an 
appropriate screen. In many cases, however, the 
green colour of caterpillars is due to the ready-made 
colour of the blood, which becomes effective when 
pigment is removed from the superficial cells, but 
which disappears when the latter are rendered 
opaque. Here, however, the superficial cells form the 
screen which has to be built up or from which the 
colour must be dismissed ; and in certain species 
even the colour of the blood is entirely changed in 
the passage from a green to a dark variety or vice 

Hence it is to be expected that the changes occur- 
ring in an insect will occupy a considerable time as 
compared with those which take place in a frog. 
Another difference between the two processes is that 


the stimulus from the environment falls upon the eye 
in the one case and probably upon the surface of the 
skin in the other. 

Variable Protective Resemblance in insects is no 
explanation of the origin of colour 

Many authorities have believed that, in the results 
of these experiments upon the colours of insects, we 
see an explanation of the origin of colour, by the direct 
influence of environment accumulated through many 
generations. This is a very tempting conclusion, and 
one which for a time appeared to me to be satisfactory. 
But as soon as there was clear evidence that the 
medium of the nervous system is necessary, the 
results were seen to be indirect, and to have needed 
the most astonishing adaptations on the part of the 
organism before the colour of the environment could 
exercise any influence upon it. 

It might still be maintaine'd that the existing 
colours and markings of certain caterpillars are at any 
rate in part due to the accumulation through heredity 
of the indirect influence of environment, working by 
means of the nervous system. To this it may be 
replied that the whole use and meaning of the power 
of adjustment depends upon its freedom during the life 
of the individual ; any hereditary bias towards the 
colours of ancestors would at once destroy the utility 
of the power, which is essentially an adaptation to the 


fact that different individuals will probably meet with 
different environments. As long ago as 1873, Pro- 
fessor Meldola argued that this power of adjustment 
is adaptive and to be explained by the operation of 
natural selection. 1 

Comparison between the varying effects of green 
leaves upon the different stages of an insect strongly 
supports the view that the results are due to adaptation. 
Thus the caterpillar of the Brimstone Moth remains 
upon its food-plant for a few weeks in the summer when 
the leaves are green, and green leaves cause the larva 
to become green and to lose the dark pigment. But 
the chrysalis remains among the leaves in winter 
when they have become brown, and green leaves cause 
the caterpillar to spin a dark cocoon. Hence precisely 
opposite effects are produced by the operation of the 
same force, the nature of the effects having been 
determined by adaptation. 

Furthermore, there is no positive evidence for any 
of these effects becoming hereditary. I have carried 
on some of my experiments for more than one genera- 
tion, always carefully noting the effects produced in 
the parents, and have never been able to detect any 
resulting hereditary tendencies, even when the previous 
generation had been powerfully influenced. 

When therefore we meet with a dimorphic species 
which is not influenced by its environment, so as to 
produce the appropriate form, I do not believe that we 

' Proc. Zool. Soc. 1873, p. 153. 


are witnessing the results of a power of adjustment 
which existed in the past but is now lost. I think, on 
the other hand, that variability or dimorphism pre- 
ceded the power of adjustment in all cases. I have 
already shown that these appearances possess a pro- 
tective value even when they cannot be adjusted (see 
pp. 46-48). When Variable Protective Eesemblance is 
present, but acts somewhat uncertainly (as in the larva 
of the Eyed Hawk Moth), it is probable that the power 
has been only recently acquired and is still imper- 
fect. This conclusion is supported by the fact that 
the closely allied caterpillar of the Convolvulus Hawk 
Moth (Sphinx convolvuli) has no power of adjustment, 
although it is completely dimorphic 1 (see pp. 47, 48). 
Before finally leaving this part of the subject I 
will briefly allude to facts which render it probable that 
certain perfect insects possess the power of Variable 
Protective Eesemblance. 

Variable Protective Resemblance probable in certain 

The colour of certain insects varies with the pre- 
vailing tint of the locality in which they occur. The 
best instance known to me is that of one of the 
Geometrce, the Annulet Moth (Gnophos obscurata). 
This moth is light-coloured in chalky localities (e.g. 
on the chalk at Lulworth), but darker when the pre- 

1 Trans. Ent. Soc. Land. 1888, pp. 552-553. 


vailing tint of the earth is dark, as in peaty districts. 
It is improbable that these are local races, and the 
only other interpretation is that the colours can be 
varied as the result of a stimulus. No experimental 
proof of this has been as yet afforded. If the view 
adopted here be correct, it will be of extreme interest 
to define the susceptible period ; it will most probably 
be found at the close of larval life. 

I have treated this part of the subject at some 
length and have discussed many details. I have done 
so because the inquiry is new, and will not be found 
in other books on the colours of animals ; l and also 
because I hope that some of my readers may be in- 
duced to carry on investigations for themselves in a 
field which is easily entered, and in which further 
help is especially necessary. 

1 Since this sentence was written, Mr. A. B. Wallace's most inter- 
esting volume, Darwinism, has appeared. A short account of Variable 
Protective Resemblance in insects will be found in it. 



WE now come to a class of colours with a meaning 
precisely opposite to that of the large class we have 
just been considering. The object of the latter is to 
conceal the possessor from its enemies, the object of 
the former is to render it as conspicuous as possible. 
As in other classes of colour, the most familiar and 
striking illustrations are to be found among insects. 1 

The sharp contrast between most Protective or Aggres- 
sive Resemblances and Warning Colours 

It must have been obvious to any one interested in 
natural history that the insects met with during a 
walk in summer may be arranged in two great groups : 
those which are extremely difficult to find and excite 
our wonder by the perfect manner in which they are 
concealed, and those which at once attract our attention 
by their startling colours and conspicuous attitudes, 
the effect being often greatly increased by the habit 

1 Many of the facts and conclusions in this chapter are taken from 
my paper in the Proc. Zool. Soc. 1887, p. 191. 


of living in companies. These two groups form, 
perhaps, the sharpest contrast in nature. We 
assume, almost as a matter of course, that the latter 
are protected in some other way, that if captured 
they would prove to be of little value, or even posi- 
tively nauseous or dangerous. 

The value of Warning Colours 

At first sight the existence of this group seems to 
be a difficulty in the way of the general applicability 
of the theory of natural selection. Warning Colours 
appear to benefit the would-be enemies rather than 
the conspicuous forms themselves, and the origin and 
growth of a character intended solely for the advan- 
tage of some other species cannot be explained by the 
theory of natural selection. But the conspicuous 
animal is greatly benefited by its Warning Colours. 
If it resembled its surroundings like the members 
of the other class, it would be liable to a great deal of 
accidental or experimental tasting, and there would 
be nothing about it to impress the memory of an 
enemy, and thus to prevent the continual destruction 
of individuals. The object of Warning Colours is 
to assist the education of enemies, enabling them to 
easily learn and remember the animals which are to 
be avoided. The great advantage conferred upon the 
conspicuous species is obvious when it is remembered 
that such an easy and successful education means an 


education involving only a small sacrifice of life. It 
must not be supposed that nauseous properties are 
necessarily attended by Warning Colours ; there are 
very many instances in which they are accompanied 
by Protective Kesemblances and habits. The common 
cockroach is a familiar example of this latter asso- 

Warning Colours in Mammalia 

The highest vertebrate animals are rarely protected 
by the possession of the qualities which-are most com- 
monly attended by Warning Colours, viz. an unplea- 
sant taste or smell. There is, however, at least one 
mammal of which this is certainly true. This ex- 
ample is brought forward hi Belt's most interesting 
book, ' The Naturalist in Nicaragua.' l Thus he tells 
us that at night ' the skunk goes leisurely along, 
holding up his white tail as a danger- flag for none to 
come within range of his nauseous artillery.' He also 
alludes to the fetid fluid which these animals ' discharge 
with too sure an aim at any assailant.' He describes 
the large white tail as laid over against the black and 
white body, producing a very conspicuous effect in 
the dusk, so that the animal ' is not likely to be 
pounced upon by any of the Carnivora, mistaking it 
for other night-roaming animals.' The conspicuous 
appearance of the skunk is shown in fig. 42. 

1 Second edition, 1888, pp. 174, 249, 250, 320, 321. See also 
Mr. A. E. Wallace's Darwinism, 1st edition, p. 233. 



I know of no instance of this kind among birds, but 
it is probable that the gaudy and strongly-contrasted 
colours of certain tropical species may be found to be 
accompanied by some nauseous property and to be of 
warning significance. 

RG. 42. The Brazilian Skunk (Afephiti* suffocant) : showing the conspicuous black 
and white appearance of the animal which serves as a warning to its enemies. 

The brilliant and conspicuous colours of many 
powerful birds are, I think, to be explained as a 
result of the free scope given to sexual selection (see 
pp. 311-12). 


Warning Colours in Reptiles 

Warning characters are not uncommon among 
poisonous reptiles. The various species of Coral 
Snake (Elaps), occurring in tropical America, are ex- 
tremely venomous, and are highly conspicuous, their 
bodies being alternately banded with bright red and 
black, and often with yellow. 1 It is extremely in- 
teresting to observe that the deadly Eattlesnake 
(Crotalus) warns an intruder of its presence by sound 
instead of by sight, like the Coral Snake. The Cobra 
is protectively coloured, but, if attacked, it expands 
the hood with the conspicuous eye-like marks, and 
thus endeavours to terrify its enemy by the startling 
appearance. The majority of poisonous snakes, how- 
ever, depend entirely upon Protective Resemblance 
together with the use of their fangs. This, for ex- 
ample, is the case with our common Viper. 

It is, however, an advantage to some snakes to 
acquire warning characters and to live on their repu- 
tation for being poisonous; for although an animal 
bitten by one of them would probably die, the effects 
are never immediately fatal, and there would be plenty 
of time for the snake itself to be killed. Again, the 
snake possesses only a limited supply of poison at any 
one time, and if this had been recently drawn upon 

1 See also A. B. Wallace's Essays on Natural Selection, 1875, 
p. 101. 


for purposes of defence or for killing prey, the snake 
would be comparatively harmless. Hence it .would 
be to the advantage of certain snakes to advertise 
publicly the fact that they are dangerous, retaining 
the poison to use if necessary ; and others would gain 
by concealing themselves by Protective Eesemblance, 
while they also would use their poison fangs if detected 
and attacked. The question is not whether one of 
these methods is better than the other, but whether 
either of them is better than an intermediate con- 
dition ; so that we can well understand why one 
group of poisonous snakes should adopt one method, 
while the other method is made use of by another 

Warning Colours in Amphibia 

Among the Amphibia a beautiful example has been 
afforded by Mr. Belt's acute powers of observation. 1 
' In the woods around Santo Domingo there are many 
frogs. Some are green or brown, and imitate green 
or dead leaves, and live amongst foliage. Others are 
dull earth-coloured, and hide in holes and under logs. 
All these come out only at night to feed, and they are 
all preyed upon by snakes and birds. In contrast 
with these obscurely coloured species another little" 
frog hops about in the daytime, dressed in a bright 
livery of red and blue. He cannot be mistaken for 
any other, and his flaming vest and blue stockings 

' Loc. tit. p. 32L 


show that he does not court concealment. He is very 
abundant in the damp woods, and I was convinced he 
was uneatable so soon as I made his acquaintance 
and saw the happy sense of security with which he 
hopped about. I took a few specimens home with me 
and tried my fowls and ducks with them, but none 
would touch them. At last, by throwing down pieces 
of meat, for which there was a great competition 
amongst them, I managed to entice a young duck into 
snatching up one of the little frogs. Instead of swal- 
lowing it, however, it instantly threw it out of its 
mouth, and went about jerking its head, as if trying 
to throw off some unpleasant taste.' It is also ex- 
tremely probable that the well-known European Sala- 
mander (Salamandra maculosd), so conspicuous with 
its irregular yellow blotches on a black ground, pos- 
sesses some unpleasant attribute. I do not think, 
however, that there is any direct evidence for this, 
like that obtained by Mr. Belt in the case of the 
Nicaraguan frog. 

Warning Colours in Marine Animals 
Many fish are poisonous, and many possess for- 
midable defensive spines, but I do not know that any 
attempt has been made to connect these characters 
with a conspicuous appearance. It is very probable, 
however, that such a connection exists in many cases. 1 

1 Mr. Garstang suggests that the weever-fish (Trachinus viper a) 
is an example of Warning Colouration. It possesses a pair of in- 


"Warning Colours are probably wide-spread among 
marine organisms. Mr. Garstang had suspected that 
the bright colours of certain compound Ascidians were 
of warning significance, because these helpless animals 
are thus rendered extremely conspicuous, and because 
some of them emit a most unpleasant odour. He now 
finds that fish invariably refuse them : although some- 
times tasted or even swallowed, they are never retained. 
The bright colours of many sea-antmones and sponges 
are probably to be explained in the same way. Evi- 
dence in favour of this conclusion is given on pp. 



Warning Colours in Caterpillars : the history of their 

Warning Colours are greatly developed in insects, 
and an account of the first recognition of this prin- 
ciple among caterpillars is of great historical interest. 
When Darwin was investigating the bright colours of 
animals, and was elaborating his theory of their ex- 
planation as of use in courtship, he came across the 
brilliant colours of certain caterpillars, and saw at 

tensely poisonous spines on its gill-covers, and is rendered conspicuous 
by a deep black first dorsal fin. The body of the fish is completely 
buried in the sand, which it resembles in colour, the black fin alone 
being seen. Mr. Garstang thinks that this conspicuous character 
prevents such fish as gurnards from mistaking the weever for the 
dragonet (Callionymus lyra), which is similar in size and habits. He 
has frequently found the dragonet in the stomachs of gurnards, but 
the weever never. 


once that they were a difficulty in the way of the 
theory. For caterpillars are undeveloped organisms ; 
they have been described as ' embryos leading an in- 
dependent life,' and there is no way of distinguishing 
the sexes by external colour or structure (except in a 
few instances). Here, therefore, we meet with bril- 
liant colours, often rendering the possessors con- 
spicuous, which cannot be of any use in courtship. 
Seeing, therefore, that the bright colours must be of 
use in some other way, Darwin drew the attention of 
Wallace to the subject, and asked whether he could 
suggest any explanation. Wallace accordingly thought 
over the subject, and considered it as part of the 
wider question of the varied uses (other than sexual) 
of brilliant and startling colour, in other stages of 
insect-life, and in numerous instances scattered over 
the whole animal kingdom ; and he finally ventured 
to predict that birds and other enemies would be found 
to refuse such conspicuous caterpillars if offered to 
them. He believed, in fact, that such larvae are pro- 
tected by possessing a nauseous taste or smell, or some 
other property which renders them unfit for food. 
Conversely Wallace argued that inconspicuous cater- 
pillars would be eaten and relished whenever they 
were detected. 

It is most inspiring to read the letter in which the 
great founder of modern biology accepted this fruitful 

' . . . You are the man to apply to in a difficulty. 


I never heard anything more ingenious than your 
suggestion, and I hope you may be able to prove it 
true. That is a splendid fact about the white moths ; 
it warms one's very blood to see a theory thus almost 
proved to be true.' 1 

Very soon after the suggestion was made public 2 
it received confirmation by experiments conducted by 
Mr. J. Jenner Weir 3 and Mr. A. G. Butler. 4 At a 
later date experiments of the same kind were made by 
Professor Weismann, 5 and still later by myself. 6 It 
was found that while birds devoured with eagerness 
the well-concealed caterpillars, they refused those 
with conspicuous colours; it was also found that 
other insect-eating animals, such as frogs, lizards, 
and spiders, refused larvae with warning colours, or 
did so after first tasting them. 

Examples of Warning Colours among Caterpillars 

A very common example of a caterpillar with 
warning colours is afforded by the larva of the Cur- 
rant Moth or Magpie Moth (Abraxas grossulariata) , 
which is excessively abundant in gardens (see fig. 43) 

1 Life and Letters of Charles Darwin, 1887, vol. iii. p. 94. 

2 Proc. Ent. Soc. Lond. Ser. 3, v. p. Ixxx. 1867. 
Trans. Ent. Soc. Lond. 1869, Part i. April. 

* Ibid. p. 27. 

Studies in the Theory of Descent, Part ii. pp. 336-340. English 
translation by Professor B. Meldola. 

6 Proc. Zool. Soc. 1887, p. 191. This paper contains an account 
of all previous work on the same subject. 



The caterpillar is extremely conspicuous, being of a 
cream colour with orange and black markings. Al- 
though it belongs to the group of well- 
concealed ' stick-caterpillars ' (Geome- 
tm), of which several instances have 
been considered in Chapter III., it makes 
no attempt to hold itself in any of the 
attitudes characteristic of its group 
(compare fig. 43 with figs. 1, 2, 3, 4, 6, 
8, and 9). All observers agree that 
birds, lizards, frogs, and spiders either 
refuse this species altogether, or exhibit 
signs of the most intense disgust after 
tasting it. 

FIG. 43. The larva 
of Magpie Moth 
(A. grosnulariata), 
showing Warning 
Colouring ; full- 
led ; natural size. 

PIG . 44. The larva of Buff-tip Moth (P. Bucephala ), 
showing Warning Colouring; full-fed ; natural 
size ; from Curtis. 

FIG. 45. The larva of Cinnabar 
Moth (E. Jaeobcece), showing 
Warning Colouring ; full-fed; 
natural size ; from Curtis. 


The caterpillar of the Buff-tip Moth (Pygaera bu- 
cephala), fig. 44, and the Cinnabar Moth (Euchelia 
jacobaa), fig. 45, are also extremely abundant, and 
are good examples of the association of Warning 
Colours with a nauseous taste. Both of them are 
gregarious, living in large companies, so that their 
conspicuous appearance is greatly intensified. The 
colours of the first-named larva are black, yellow, and 
orange. It feeds on oak, elm, lime, birch, hazel, &c., 
and the large bare branches which attest its appetite 
are very familiar sights in autumn. The second 
caterpillar is coloured by alternate black and yellow 
rings ; it feeds upon ragwort in the summer. There 
is plenty of experimental evidence for the unpleasant 
taste of both caterpillars. 

The conspicuous gregarious caterpillars of the 
Large Garden White Butterfly (Pieris brassicce), which 
are only too well known in cabbage gardens in the 
autumn, are also protected in the same manner. 
Many other instances will be found in the papers 
already referred to. 

A caterpillar may be freely exposed rather than 

In some cases the warning of an unpleasant 
quality is conveyed by the caterpillar being freely 
exposed, while its colours, although sober, do not 
harmonise with those of the food-plant. This may 


be true of gregarious species, such as the dark larvae of 
the Peacock or Small Tortoiseshell butterflies, which 
feed freely exposed on the tops of nettles, and which are 
known to be refused by some insect-eating animals. 1 

The various unpleasant qualities possessed by 
caterpillars with Warning Colours 

Other unpleasant attributes, as well as that of 
a nauseous taste, may be associated with Warning 
Colours. A strongly smelling or irritant fluid may be 
discharged from special glands on the approach of an 
enemy. Glands of this kind occur on the back of 
many common caterpillars, such as the brilliantly 
coloured ' Palmer worm ' (larva of Porthesia auriflua), 
or the onspicuous ' Hop-dog ' (larva of Orgyia 
pudilunda). The larvae of some common gregarious 
saw-flies (Hymenoptera), such as Croesus septentrionalis, 
which completely denudes the branches of birch trees, 
have a number of odoriferous glands along the middle 
of the ventral surface. When disturbed, the body is 
turned forward over the head, and the glands are 
everted so that their secretion escapes into the 
air. The meaning of the gregarious habit is very 

1 The gregarious habit may render an insect so conspicuous that 
it is unnecessary for it to acquire bright colours. The ' warning ' 
significance of the gregarious habit was first suggested by Fritz 
Miiller (Kosmos, Dec. 1877). An abstract of this paper has been 
published by Professor Meldola (Proc. Ent. Soc. Lond. 1878, pp. vi. 
and vii.) 


clear in this and parallel cases ; for when many indi- 
viduals combine to discharge an unpleasant odour, 
they become surrounded by an atmosphere which acts 
as a most effective barrier. 

Irritating hairs possessed by certain larvae 

Again, caterpillars may be protected by possessing 
irritating hairs. This is the" case with the ' Palmer 
worms ' mentioned above, which are thus doubly pro- 
tected. Many people have discovered this fact to 
their cost after handling these pretty black, red, and 
white caterpillars, which are so abundant and freely 
exposed on our hawthorn hedges in early summer. 
When the face or neck is touched by the hands, which 
are covered with minute barbed hairs shed by the 
caterpillar, an intensely irritating rash soon makes its 
appearance. The same effect is produced, as I shall 
always remember, if an old cocoon, in which the hairs 
are interwoven, be pulled to pieces with the fingers. 
These caterpillars were nearly always refused, but Mr. 
Butler records that they were in one case eaten with- 
out hesitation by a young sky-lark, which soon after- 
wards died with symptoms which may have been due 
to the irritating hairs. . One of my lizards also seized 
a larva, but relinquished it after biting it for sometime. 
The lizard was evidently greatly irritated by the hairs 
in its mouth. Many other hairy caterpillars also 
produce a rash : thus, the larvae of the Fox Moth 


(Lasiocampa rw&t),0ak Eggar (L. quercus), and Drinker 
(Odonestis potatorid), have this effect on the skin of 
the hands if they are held for a long time, and they 
would certainly act rapidly upon the delicate skin of 
the mouth. All thre.e caterpillars are fairly con- 
spicuous, and there is experimental evidence that the 
two latter are disliked. 

It will be shown that the hairs are sometimes 
arranged in tempting tufts, which invite an enemy to 
seize the caterpillar at a point which does not injure 
the latter, while it causes the former the greatest dis- 

The hairs of nearly all caterpillars are probably 
more or less unpleasant in the mouth. Delicate and 
sensitive animals, such as the marmoset, although ex- 
cessively fond of insects, cannot be induced to touch 
any hairy larva. Birds appear to eat them more 
readily than other animals, but they have peculiar 
advantages in their power of rubbing off the hairs. 

The association of hairs with a conspicuous appearance 

Sir John Lubbock l has tabulated the appearance 
of the larvae of all British butterflies and the larger 
moths, and he thus shows in a most convincing 
manner the general association of hairs or spines with 
conspicuous warning colours. His conclusion is as 
follows : ' Thus summing up the caterpillars, both of 

1 Trails. Ent. Soc. 1878, pp. 239, et sej. 


the butterflies and moths, out of the eighty-eight spiny 
and hairy species tabulated only one is green (L. 
syUlla), and even this may not be protectively coloured, 
since it has yellow warts and white lateral lines. On 
the other hand, a very great majority of the "alack and 
brown caterpillars, as well as those more or less 
marked with blue and red, are either hairy or spiny, 
or have some special protection.' ) 

Sir John Lubbock, however, fully recognises that 
hairs may contribute towards tb Protective Eesem- 
blance of certain species, examples of which have 
been already given (see page 35). Professor Meldola 
suggests that a probable original meaning of the hairy 
covering was protection from injury after falling from 
the food-plant. 

Warning Colours in other stages of metamorphosis in 

Lepidoptera of many species are protected by 
Warning Colours and unpleasant attributes, in other 
stages in addition to that of the larva ; and the same 
method of defence is also adopted in other orders of 
insects. The chrysalis of the Magpie Moth, which is 
black with yellow bands, and exposed to view in a very 
slight cocoon, is nauseous like the larva, and the slow- 
flying moth itself, with white wings rendered conspicu- 
ous by yellow markings and black spots, is defended in 
the same manner. When captured it makes no attempt 


to escape, but ' feigns death.' The conspicuous and 
sluggish day -flying black and red Burnet Moths 
(Zygcena) and Cinnabar Moth (Euchelia Jacobcece) are 
also nauseous, and so is the gaudy Garden Tiger Moth 
(Arctia caja). Many white moths, or black and white 
moths, have also been refused by insect-eating animals 
with every sign of disgust. 

Consideration of the later stages of species with 
unpalatable larv 

A comparison of the means of defence and palata- 
bility in the three stages of metamorphosis, in species 
of which the larvae are known to be nauseous, proved to 
be extremely interesting, and much more work is needed 
in the same direction. In the first place the com- 
parison showed that when the later stages are nauseous 
the larva was also nauseous in all cases. The Tiger 
Moth is probably an exception, for the caterpillar may 
be defended by its hairs instead of by taste, and the 
chrysalis seems to be palatable. The Leopard Moth 
(Zeuzera cesculi] is another exception. Such cases are 
probably very rare, and it is clear that this method of 
defence, among Lepidoptera, nearly always arose in 
the larval stage. The larval stage is exposed to more 
danger and is more helpless than any other : the 
imago can escape by flight, and the pupa, if exposed, 
may render its Protective Resemblance complete by 
entire quiescence, and it is usually effectually protected 


in other ways. But the larva must feed, and at the 
same time is sluggish in its movements, defenceless, 
and when palatable is more relished than any other 
stage, for it does not possess the hard investment of 
the one or the scaly covering of the other. Hence it 
is that the great needs of the larva have been so fre- 
quently met in this way; but as soon as the un- 
pleasant quality has appeared it will tend to pass on 
by simple continuity into the other stages. If these 
latter are hard pressed, there is always the possibility 
that such qualities may be made the starting-point of 
a similar method of defence for them also. But the 
disagreeable properties may also pass on into stages 
which hold their own successfully by elaborate and 
perfect Protective Eesemblances, and then such quali- 
ties, unattended by Warning Colours, are entirely use- 
less to the stage, but may be important as a latent 
possibility for the future. It must be remembered 
that an unpleasant attribute must always appear in 
advance of the warning colouring. An example is 
afforded by the Buff-tip Moth (Pygcera Imcephala), 
which is beautifully protected, during rest, by resem- 
bling a piece of rotten lichen -covered stick (see page 
57), but which nevertheless retains something of the 
unpleasant taste by which its caterpillar is effectually 


The metallic appearance of certain pupae may be of 
value as a warning 

At this point it is of interest to consider the cases 
in which the metallic appearance of a chrysalis may 
act as a warning. Dr. Fritz Miiller tells me that the 
brilliant metallic pupae of the South American butter- 
fly, Mechanitis lysimnia, hang in groups from the 
leaves of their food-plant (Solanum). The butterfly of 
this species is certainly distasteful, for the genus is 
mimicked by butterflies of other families. This fact, 
and the gregarious habit of the pupae, render it nearly 
certain that the glittering appearance has a warning 
significance. The same is probably true of the pupa 
of the abundant Indian butterfly (Euplcsa core), which 
Mr. E. A. Minchin tells me possesses a brilliant silvery 
appearance, and is so conspicuous that it can be seen 
from a great distance. This butterfly also belongs to 
a group protected by an unpleasant taste or smell, 
and there is little doubt that the metallic appearance 
of the pupa has a warning meaning. 

Warning Colours in other orders of Insects 

Passing now to the other orders of insects, highly 
conspicuous and abundant beetles (Coleoptera), such 
as the black and red ' soldiers and sailors ' (Tele- 
phorus], the red and -black ladybirds (Coccinella), and 
the red and blue-black Chrysomela populi, have been 


shown to be extremely nauseous, and the two latter 
emit a very unpleasant smell. 

The sting possessed by the females of so many 
Hymenoptcra is obviously an unpleasant attribute, . 
rendering the insect disagreeable or even dangerous to 
eat. We find accordingly that stinging insects are 
often rendered conspicuous by warning colours, of 
which the contrasted dark and yellow bands of the 
Common Wasp, the Hornet, and of many Humble 
Bees, furnish examples. 

Warning Colours are also to be found in other 
orders, but it is unnecessary to give further examples. 
They will be recognised in numbers in any country 
walk during the summer, although the experimental 
proof of the co-existence of some unpleasant attribute 
is still wanting in a large proportion of the cases. 

Warning Colours can only be safely adopted by a small 
proportion of the Insects in any country 

The acquisition of an unpleasant taste or smell, 
together with a conspicuous appearance, is so simple 
a mode of protection, and yet apparently so absolutely 
complete, that it seems remarkable that more species 
have not availed themselves of it. What can be the 
principle which works in antagonism to such a mode 
of protection? Thinking over this subject, as the 
result of a lecture upon the facts and conclusions 
already described, 1 it appeared probable that such an 

1 Delivered at the Royal Institution in the spring of 1886. 


antagonistic principle would be found in the too com- 
plete success of the method itself. If a very common 
insect, forming the chief food of some animal, gained 
protection in this way, the latter might be forced to 
devour the unpalatable food in order to avoid starva- 
tion. And the same result might readily be brought 
about if a scarce and hard-pressed form adopted the 
same line, and became dominant, after ousting many 
species which were important as food. If once an 
insect- eating species were driven to eat any such 
insect in spite of the unpleasant taste, it would gradu- 
ally come to devour it with relish, and the insect 
would be in great danger of extermination, because 
of its conspicuous appearance. 

If this reasoning be correct, it is clear that the 
mode of defence is by no means perfect, and that it 
depends for its success upon the existence of relatively 
abundant palatable forms ; in other words, its employ- 
ment must be strictlv limited. 

Absence of Warning Colours in the seasons when 
Insect life is scarce 

A very interesting fact in support of this argument 
is the entire disappearance of all insects with Warning 
Colours during the seasons when insect life is scarce, 
and when insect-eating animals are hard pressed for 
food. And yet, if it were safe to rely on such a mode 
of defence, the Warning Colours would be especially 


conspicuous at these times, when all the tints of nature 
are sombre and form a background against which the 
Warning Colours would stand out in startling contrast. 
Certain species, which are defended in this way, pass 
the winter in the brightly coloured stage of metamor- 
phosis ; but they conceal themselves as completely as 
possible under loose bark or among dead leaves, &c. 
This is true of the common ladybird, and I have 
noticed that they begin to hide comparatively early in 
the autumn, when the insects are rapidly diminishing 
in numbers, but before the beginning of the cold 
weather. It is therefore probable that they hide in 
order to conceal their bright colours and not to escape 
the cold.- It is also known that ladybirds are eaten 
by the Green Tree frog in winter, when other insect 
food is scarce, and also by hungry birds, although 
they are intensely disliked and are refused (at any rate 
by the frogs) if other food can be obtained. 

Experimental proof that Insect-eating animals, if 
hungry, will eat unpalatable species 

This conclusion was tested as completely as pos- 
sible by offering conspicuous unpalatable insects of 
many species to animals from which all other food 
was withheld. Under these circumstances the insects 
were eaten, although often after many attempts, and 
evidently with the most intense disgust. 


Natural selection has enabled certain animals to eat 
unpalatable Insects with apparent relish 

Naturalists have always recognised that an insect 
may be distasteful to one animal, but palatable to 
another. It is, however, very probable that these 
differences have been acquired comparatively recently, 
and have arisen out of the competition for food. In 
most cases the change of habit has not become so far 
confirmed that the previously distasteful food is eaten 
with avidity and pleasure. Again, when we find that 
the taste of an insect is recognised as nauseous by a 
standard wide enough to include mites and spiders as 
well as birds, lizards, and frogs, it appears probable 
that any difference of opinion is due to an altogether 
exceptional immunity conferred upon certain species 
by natural selection. 

Nauseous qualities probably do not affect Insect 

It is probable, however, that this argument does 
not apply to insect parasites, which are not in the 
position to gratify their tastes, but must make the 
best of the larva in which the parent has deposited 
her eggs. It is clear that even the most nauseous 
forms must suffer greatly from the attacks of enemies, 
for the average number of individuals in each species 
appears to remain constant. It is likely that the 


numbers are kept down by special liability to the 
attacks of insect parasites, in one or more stages. 
Thus the larva of the Large Garden White (Pieris 
brassicte) is known to be nauseous, but the im- 
munity from attack which it enjoys by no means 
extends to its insect foes. In the autumn of 1888 I 
collected some hundreds of these larvae in order to 
experiment upon the colours of their pupaa. I ob- 
tained 109 pupae, while 424 mature larvae died from 
the presence of the parasitic grubs of Ichneumon flies 

The likes and dislikes of Insect-eating animals are 
purely relative 

It may be taken as proved that the continued 
spread of some distasteful form and the correspond- 
ing diminution of edible species would lead to the 
former becoming the prey of insect-eating animals ; 
for a point would ultimately be reached, as it was 
reached in many of my experiments, when hunger 
would become a stronger stimulus than those lesser 
prejudices in which a species can very well afford to 
indulge while palatable food is abundant. These pre- 
judices having been overcome in confinement, there is 
nothing in the conditions of natural life which could 
prevent the same result from being reached, as doubt- 
less it has been reached again and again. The com- 
parison of all experiments of this kind ever made with 
insects will show that the likes and dislikes of insect- 


eating animals are purely relative, and are manifested 
to a marked extent when they are offered a variety 
of insects, and when obviously nauseous species are 
excluded from the list. 

Butterflies and moths are freely eaten by lizards, 
but they are not enjoyed like houseflies or many cater- 
pillars. This is probably because the former are such 
dusty and unsatisfactory things to eat, with such a 
small proportion of body in which the nutriment and 
taste is contained, and so large an expanse of dry 
membranous wings with their scaly covering. In 
this respect butterflies contrast unfavourably with 
moths, and the latter are certainly greatly preferred by 
lizards and especially birds. The latter have special 
advantages in being able to pick off the wings before 
eating the body. 

In the excessive abundance of insect-eating ani- 
mals and the keen competition for food which takes 
place, we see the conditions which must render the 
acquisition of an unpleasant taste together with Warn- 
ing Colours an exceedingly hazardous mode of defence, 
if assumed by more than a small proportion of the 
insects of a country. For in so great a press of com- 
petition among the innumerable insect-eaters, we 
may feel sure that some at least would be sufficiently 
enterprising to make the best of food which at least 
has the advantage of being easily seen and caught. 

The great principle of Warning Colours has de- 
servedly taken a most important place among the 


principles which deal with the infinitely complex and 
ever-changing relations which obtain between the 
most widely separated, no less than between the most 
closely allied, members of the organic kingdom. But, 
nevertheless, this principle carries with it its own 
compensating principle, which will come into opera- 
tion precisely as the former advances to the possession 
of undue influence. 

The education of enemies assisted by the fact that 
Warning Colours and patterns often resemble each other 

It is probably unnecessary for the young insect- 
eating animal actually to make trial of every species 
of nauseous insect in its locality, in order to be 
equipped with an efficient stock of experiences with 
which to conduct its later life. Such an education 
would be somewhat dearly bought ; it would be un- 
pleasant to the insect-eater and destructive to the 
insect. Since, however, the same colours are em- 
ployed again and again by unpalatable or dangerous 
insects of very different groups, and since the patterns 
are also frequently repeated, it is obvious that a com- 
paratively few- unpleasant experiences would be suffi- 
cient to create a prejudice against any insect with a 
colour or pattern at all resembling the nauseous forms 
which had already produced BO deep an impression 
upon the memory. 

This conclusion was drawn from the careful com- 
parison of the colours and patterns of all insects which 


have been experimentally shown to be distasteful. 
The colours which produce the greatest contrast, and 
therefore the greatest effect, upon the eye of an insect- 
eating Vertebrate, are black and white, and next to 
this black (or some very dark colour) and yellow, 
orange, or red ; and it was found that nearly all 
unpalatable or dangerous insects were coloured with 
these tints. The advantage gained by the acquisition 
of such colours is twofold : they afford the combina- 
tions which are most conspicuous to an enemy, and 
their number being small, while nauseous forms are 
numerous, the continual repetition of the same com- 
bination becomes a necessity, and this also facilitates 
the education of enemies. 

There are similarly a few eminently conspicuous 
and simple patterns. These are alternating rings of 
different colours, and alternating longitudinal stripes, 
both especially suited to the cylindrical body-form, 
such as that of caterpillars, &'c. ; spots upon a back- 
ground with a contrasted colour, especially suited 
to a wide expanse such as the wings of Lepidoptera. 
Every insect which has been proved to be distasteful 
was found to possess one or other of the above patterns 
or some combination of them. Here also the frequent 
similarity of the patterns of nauseous insects is 
primarily due to the fact that there is only a limited 
number of appropriate patterns, but also because the 
repetition is in itself advantageous and has therefore 
been encouraged by natural selection. 


Some of the advantages of true mimicry (to be 
more fully described below) also follow, when a group 
of insects is rendered conspicuous by the same 
colours and patterns, and when certain members of 
the group are noted for the possession of especially 
unpleasant attributes. Thus it is more than probable 
that the species marked by alternate rings of black 
and yellow (including the chrysalis of the Magpie 
Moth and the caterpillar of the Cinnabar Moth), gain 
considerable advantages from the justly respected 
appearance of Hornets and "Wasps. It must not be 
forgotten, however, that the latter also are probably 
benefited, although to a much smaller extent, by the 
greater publicity which follows from the resemblance. 

The causes which have determined the resemblance 
between Warning Colours in different Insects 

Hence the causes which determine the frequent 
repetition of the same colours and markings in dis- 
tasteful forms are as follows: (1) The fact that a 
limited number of colours and patterns are especially 
efficient in attracting the attention of enemies, and in 
thus facilitating their education; (2) the fact that 
the education of enemies is also rendered easy by 
requiring them to learn only a small number of pat- 
terns and colours ; (3) the great additional advantage 
conferred by trading upon the reputation of a well- 
known and much-feared or much -disliked insect. 



The warning appearance acquired by any insect is 
also largely determined by the character of its previous 
appearance, which formed the material upon which 
at any rate the first steps of the change were built. 

In some cases we can successfully read the history 
of past changes, and can point to certain parts of a 
warning appearance which are remnants of a previous 
mode of defence by means of Protective Eesemblance. 

Thus the orange rings of the caterpillar of the 
Cinnabar Moth harmonise 
well with the flowers of its 
food - plant, ragwort. 1 The 
acquisition, or perhaps only 
the greater prominence, of 
the strongly contrasted black 
bands, and above all, the 
gregarious habits, are the 
later developments which have 
followed the acquisition of an 
unpleasant taste. Again, the 
caterpillars of the Mullein 
Moth (Cucullia verbasci), which 
are so abundant and con- 
spicuous on various species of 
Mullein (Verbascum) , are even 
now difficult to detect when 
resting among the dark and 
yellow sessile flowers studded upon the surface of the 

1 First noticed by T. W. Wood : Insects in Disguise, Student. 


FIG. 46. Two larvae of Mullein 
Moth (Cucullia verbasci) on 
the spike of the Mullein ; small 
in last stage ; natural size. 


thick green spike (see fig. 46). ! The conspicuous 
appearance chiefly depends upon the gregarious 
habits, and upon the fact that the larvse com- 
monly rest on the upper surface of the large leaves, 
which form a background against which the larval 

PIG. 47. Larva of Mullein Moth on leaf of Mullein ; full-fed ; natural siza 

colours stand out with startling distinctness (see fig. 
47). It has been proved that these larvae possess an 
unpleasant although not an extremely nauseous taste, 
so that here also we have evidence that the change 
from a palatable well-concealed form is only recent 
and is as yet incomplete. 

* This observation w&s ^o^^p^.tiDicfttod to Professor ^kltddolci by 
Mr. Thomas Eedle. 


WARNING COLOURS (continued) 

Sexual colouring may be made use of for warning 

In addition to the modes of producing a warning 
appearance which we have hitherto considered, and 
which are almost universal in this country, there is 
another method which is very conspicuous in the 
tropics. In certain groups of mature insects, and 
especially in butterflies, the beautiful colours and 
patterns which have been produced by courtship, 
appear to have been made use of as an indication of 
some unpleasant quality. 

The differences between Sexual and Warning Colours 

The tints used in and produced by courtship are 
as a rule easily distinguished from Warning Colours, 
even when both occur in sexually mature insects. 
The former rarely usurp the whole surface of an in- 
sect, and they are carefully concealed during repose. 
Thus the upper sides of the upper wings of most 
moths, and the under sides of both wings in butter- 


flies, are generally protectively coloured, and hide the 
bright colours of other parts when the insect is at 
rest. If the parts exposed during rest are conspicu- 
ously coloured it is clear that they chiefly possess a 
warning significance. I say ' chiefly,' because it is 
probable that the appearance of the mature individuals 
of any species, however much it may be specialised for 
other ends, possesses a sexual significance, and appeals 
as an adornment to the modified taste of the individuals 
of the same species. We have a rough criterion of 
the extent to which the taste has been modified when 
we compare the appearances which have other addi- 
tional meanings with those which possess a sexual 
value alone, and which are concealed except during 
flight and are especially displayed in courtship. 
Warning Colours are also displayed during the slug- 
gish flight of a nauseous species, but the insects with 
purely ornamental colours are swift and wary when 
upon the wing. 

But quite apart from these considerations, the 
Warning Colours can be distinguished by the subordi- 
nation of every other feature to that of conspicuous- 
ness. Crude patterns and startling strongly contrasted 
colours are eminently characteristic of a warning 
appearance, while the colours and patterns produced 
by courtship include everything that is most beautiful 
in insects. The two kinds of appearance differ as an 
advertisement differs from a beautiful picture: the 
one attracts attention, the other excites admiration. 


The transition from Sexual to Warning Colours 

The two groups nevertheless run into each other, 
and a beautiful transition is afforded by the insects 
in which sexually produced colours and patterns are 
made use of for warning purposes. When this is the 
case the colours spread on to the parts which are ex- 
posed during rest, and the flight becomes sluggish, so 
that they are displayed as completely as possible. 
These are the insects which are the principal models 
of mimicry in tropical countries, and Bates's classical 
paper, in which an intelligible theory of mimicry was 
first brought forward, deals with the groups which are 
found in the Amazon valley, and with the forms which 
resemble them and share the advantages conferred by 
their well-known and nauseous qualities. The evi- 
dence for the existence of such qualities is better 
considered under the next heading, viz. Mimicry. 

Resemblance between such Warning Colours in different 

The members of each of these groups resemble one 
another to a marked extent ; far more so than the 
species of other groups without Warning Colours. 
Thus the advantage of facilitating the education of 
enemies is gained by them, although it has arisen in a 
manner different from that already described in other 
unpalatable insects (see pp. 184-86). 


The similarity has arisen from the fact that the 
species in each group are closely related, so that 
natural selection has maintained an initial resem- 
blance, instead of causing convergence, as it has done 
with more distantly related species. Hence repetition 
of the same appearance may be produced by a pre- 
vented divergence, as in these cases, or by the actual 
convergence of forms originally unlike, as in the former 

The convergent forms are more perfectly con- 
spicuous, more ideally warning, because they have 
been further modified from their original appearance ; 
while the forms in which divergence has been arrested 
have merely adopted, with comparatively slight modi- 
fication, an appearance which was produced by the 
operation of other principles, but which is sufficiently 
well known for the purpose. 

These interesting conclusions have gradually grown 
out of the observations of many naturalists. 

The arrested divergence, sometimes aided by actual 
convergence, has produced such remarkable resem- 
blances between certain species of unpalatable insects, 
that Bates speaks of the wonderful fact that such 
species mimic each other. Wallace at first looked 
upon these mysterious resemblances as due to some 
unknown cause connected with locality, for the 
similar species are nearly always found together. 

The difficulty was at length explained by Fritz 


Miiller. 1 This eminent naturalist suggested that both 
species were benefited by the resemblance, because 
the number of individuals which must be sacrificed to 
the inexperience of young birds and other enemies 
would be made up by both of them instead of by each 
independently. This fruitful suggestion was at once 
accepted by Wallace. 2 The mathematical aspects of 
the subject were accurately worked out by Mr. Blakis- 
ton and Mr. Alexander, of Tokio, Japan. 3 

The next step was taken by Professor Meldola, 4 
who extended Fritz Miiller's explanation of these 
comparatively rare cases of close resemblance, to the 
general similarity which obtains throughout whole 
groups of unpalatable and conspicuous species. ' The 
prevalence of one type of marking and colouring 
throughout immense numbers of species in protected 
groups, such as the tawny species of Danais, the 
barred Heliconias, the blue-black Euplceas, and the 
fibrous Acrceas, is perfectly intelligible in the light of 
the new hypothesis.' 

This list comprises the whole of the large groups 
of butterflies alluded to in the last few pages. The 
species belonging to them are very familiar in every 
collection of tropical butterflies, while some of them 
are even abundant in temperate climates. Until re- 

1 Ituna and Thyridia, Kosmos, May 1879, p. 100, translated by 
Meldola, Proc. Ent. Soc. Lond. 1879, p. xx. 

2 Nature, vol. xxvi. p. 86. 

* Ibid., vol. xxix. p. 405. 

* Ann. and Mag. Nat. Hist. December 1882. 


cently, the British butterflies did not include an ex- 
ample, but a large and handsome American Danaid 
(Danais archippus) seems to be gradually extending 
its range into every country where the food-pla.nts 
(Asclepiads) of its larva are to be found. Several 
individuals have been caught in this country of late 

FIG. 48. The North American Dnnais arch'ppus, which has now spread into 
this country ; upper side ; iiiUI natural size. 

Pl&. 49. Danriis archippus, showing the conspicuous colours on the under 
sides of the wings. 

years, and there is no doubt that it will thoroughly 
establish itself if it can meet with a sufficient supply 
of larval food, and can withstand the ceaseless energy 
of collectors. It is far larger than any of our native 
butterflies. It is shown half the natural size in 
fig. 48, while fig. 49 gives the appearance of the 
under side. The latter figure shows that the insect 


must be as conspicuous at rest as it is on the wing, 
a fact which is characteristic of those groups of 
butterflies which are specially defended by being un- 
palatable. In North America Danais archippus is 
mimicked by Limenitis misippus, a butterfly belonging 
to a very different group. 

Although the general resemblance between the 
species in each of these groups is doubtless due to 
arrested divergence, there is one very interesting 
case which is probably to be explained by convergence 
of groups which were formerly unlike. The Danaids, 
which are found in the same localities as the Heli- 
conias of tropical America, have taken the peculiar 
appearance of the latter, in the arrangement of the 
colours, and in the long narrow form of the wings. 
These Heliconoid Danaids are therefore distinguished 
from all the other members of the group. It is quite 
obvious that both Heliconian and Danaids are benefited 
by the fact that the insect-eating animals of the region 
they inhabit have to learn but a single mode of flight, 
shape of wing, and general arrangement of colours. 

Although these resemblances, produced by conver- 
gence or by arrested divergence, are transitional into 
and often contain an element of true Mimicry, they 
must be distinguished from the latter. In true 
Mimicry, the mimicking species are without unplea- 
sant attributes, and are sheltered under the reputation 
of abundant and well-known forms in which such 
attributes are strongly marked. In the resemblances 


considered here, all the similar forms possess unplea- 
sant attributes although they may possess them in 
different degrees. 

The remarkable likeness between many of the 
species of Burnet Moths (Zygaenidae) is probably due 
to arrested divergence. They are all conspicuous 
black and red moths, and some of them are known 
to be nauseous. 

The unpleasant qualities may be concentrated in special 
parts, which are so placed and coloured as to attract 
the attention of enemies 

In certain cases the warning appearance is of a 
different kind. The organism possesses a highly 
conspicuous feature to which the attention of an 
enemy is directed ; if seized, the structure breaks off 
without harm to the animal, but with very unpleasant 
results to the enemy. It is probable that this method 
of defence will be found to be wide-spread. 

The defensive value of ' tussocks ' 

Only recently, in the summer of 1887, this ex- 
planation of the beautiful flat-topped tufts of fine 
hairs, called 'tussocks,' which occur on certain cater- 
pillars, was shown to me by the results of an experi- 
ment. 1 The tufts are often light-coloured, and are 

1 Trans. Ent. Soc. Lond. 1888, pp. 589-91. 


generally placed on an intensely black ground colour, 
which shows them up and makes them appear to 
project more than is actually the case. In the well- 
known ' H'op-dog ' or ' Tussock ' caterpillar (Orgyia 
pudibunda) there are four ' tussocks,' each upon a 
separate ring, and the furrows between these rings 
are of the most intense velvety black. They are con- 
cealed until the caterpillar is irritated, when the body 
is curved in a vertical direction, so that the * tussocks ' 
diverge, and the furrows appear as black semilunar 
areas separating them and rendering them con- 
spicuous. The hairs of the ' tussocks ' are so fine and 
so closely packed that the tuft does not appear to be 
made up of hairs at all, but to be rather a fleshy pro- 
jection from the back of the caterpillar, and a most 
convenient part for an enemy to seize. Fine as the 
hairs are, they nevertheless bristle with minute lateral 
branches, and would certainly be most unpleasant if 
brought into contact with the skin of the mouth. If 
seized by an enemy, the fine hairs come out in im- 
mense numbers, and produce such an effect upon 
the skin of the mouth that the caterpillar escapes 

The following experiment suggested the explanation 
which has just been given. A caterpillar of the 
Common Vapourer Moth (Orgyia antiqua) was intro- 
duced into a lizard's cage, and when attacked, instantly 
assumed the defensive attitude, with the head tucked 
in and the ' tussocks ' separated and rendered as 


prominent as possible. An unwary lizard seized the 
apparently convenient projection ; most of the ' tus- 
sock ' came out in its mouth, and the caterpillar was 
not troubled further. The lizard spent a long and 
evidently most uncomfortable time in trying to get rid 
of its mouthful of hairs. 

On another occasion a full-grown ' Hop-dog ' was 
offered to a hungry adult Lacerta viridis, but the 
lizard knew the danger, and kept trying to find some 
part of the body which could be safely seized. The 
caterpillar remained motionless in the defensive 
attitude during the whole attack, which lasted several 
minutes. In this attitude the ' tussocks ' were held 
in the most tempting manner, while all other parts of 
the body bristled with sharp stiff spines. This ex- 
perienced lizard finally seized the back of the larva 
a long way behind the ' tussocks,' evidently looking 
upon the bristles as the lesser evil. Although killed 
the caterpillar was not swallowed, and it had only been 
seized after many attempts and the closest examina- 
tion. It is quite clear that the hairy covering would 
have saved it from any except a very hungry enemy. 

Evidence that Insect-eating Animals learn by experience 

When we compare the behaviour of these two 
lizards we find strong evidence for the opinion that 
insect-eating animals learn by experience. I have, 
however, come across more direct and convincing 


proofs of this conclusion. Thus, the chamseleon which 
has been previously referred to had just been imported 
into this country when I received it, and it had probably 
never seen a common hive-bee in its life. I put a living 
bee in the cage, and the lizard immediately began to 
watch it, and, as soon as it had settled, captured it 
with a dexterous shot of its long tongue. As the 
tongue was being withdrawn with the bee adhering to 
the sticky pad at its extremity, the chamaeleon was 
stung and immediately showed signs of discomfort, 
throwing its head from side to side, and thus jerking 
the bee off. For many months after this I put 
bees into the cage at irregular intervals; but the 
chamseleon's education in this direction was complete, 
the single experience was sufficient, and no other bee 
was touched. 

Similar highly-coloured and specially defended features 
occur in certain Marine Animals 

A very similar example from an entirely different 
group of animals has been recently brought forward 
independently by Professor W. A. Herdman l and Mr. 
Garstang. These naturalists suggest that the brightly- 
coloured dorsal papillae of Eolids (Nudibranchiate 
gastropods) have the same meaning as the ' tussocks ' 
of Orgyia, being far more conspicuous than the rest 
of the body, easily detached, and often reproduced by 

1 Report of British Association at Neivcastle, 1889. 


growth in two or three days. The nematocysts at the 
tips of the papillae would convey a lesson to the enemy 
similar to that taught by the fine hairs of the 'tussocks.' 

Mr. Garstang has now tested this suggestion by 
experiment, and he finds that fish will not attack the 
Eolids under normal conditions. He therefore threw 
one of them (the orange variety of Cavolina Farrani) 
into the tank containing young pollack (Gadus polla- 
chius), which generally swallow any object while it is 
descending to the bottom. The Eolid was swallowed 
and rejected after a second or two by two fish, which 
then shook their heads as if experiencing discomfort. 
Similar movements were made when the fish were 
induced to seize the specially defended tentacles of sea- 
anemones, and when they attempted to swallow the 
Poly cirrus, described on p. 201. Mr. Garstang then 
found that the Eolid causes a distinct, though faint, 
tingling sensation when placed on the tongue ; while 
larger species (Facelina coronata and Eolis Alderi) 
produce much more marked effects. 

The protectively coloured Opisthobranch, Hermeea 
(see p. 70), has well-developed defensive papillae, 
and Mr. Garstang finds that whenever a shadow 
passes over it, the head is at once retracted, and the 
papillae rendered very prominent. This behaviour is 
exactly similar to that described in the larvae of Orgyia 
(see pp. 197-98). The reaction under the stimulus 
of light is associated with the unusually large eyes of 
the genus. 


Mr. Garstang has still more recently come across 
an instance of the same kind in a bright red marine 
worm, one of the Terebellidce (Poly cirrus aurantiacus), 
which, unlike the rest of its family, has dispensed 
with the protection of a tube, and creeps about in the 
crevices of stones and among the roots of Laminaria. 
It has an immense number of long, slender- tentacles, 
and when touched, coils itself up in the middle of them. 
The tentacles break off very easily, and evidently possess 
some unpleasant attribute. When the animal is irri- 
tated the tentacles become brilliantly phosphorescent, 
so that they are conspicuous by night as well as day. 
Mr. Garstang obtained experimental evidence of the 
validity of this interpretation. He placed a specimen in 
one of the fish-tanks in the Plymouth Laboratory : only 
one pollack ventured to seize the worm, but ejected it 
immediately, and would not touch it again. Another 
fish made three vigorous attempts to swallow it, but 
finally left it. Another, a very voracious rock-fish, ac- 
tually swallowed it, but immediately afterwards began 
to work its jaws about as if experiencing discomfort. 
Mr. Garstang then cut the head and tentacles away from 
the body and threw both pieces into the pollack tank : 
the tentacles were untouched, but a fight took place 
over the body, which was torn into several pieces and 
swallowed with great relish. Mr. Garstang has kindly 
allowed me to describe these interesting experiments, 
which have only just been made, and have not, as 
yet, been published elsewhere. 


Adventitious warning colours 

Under this head we may include a few very in- 
teresting cases in which palatable animals make use 
of others which are specially defended and conspicuous 
in order to gain protection. Such a method of defence 
bears the same relation to Warning Colours as the 
examples of Adventitious Protection and Colouring 
bear to true Protective Eesemblance (see pp. 76-80). 

A mollusc which encourages a dense growth of 
algae upon its shell is defended by Adventitious Pro- 
tective Eesemblance ; if, however, the algae were 
brilliantly coloured and nauseous or poisonous, the 
example would fall under Adventitious Warning 

Professor Eomanes l brings forward examples of a 
most interesting association of crabs with sea- 
anemones. He quotes from Mobius 2 the remarkable 
case of * two crabs belonging to different genera which 
have the habit of firmly grasping a sea-anemone in 
each claw, and carrying them about ; ' also from P. H. 
Gosse 3 the fact that when the sea-anemone (Adamsia 
palliata) is removed from its position upon the shell 
of the hermit crab (Pagurus Prideauxii), which in- 
variably carries it, the crab 'always took it up in 

1 Animal Intelligence, International Science Series, pp. 233-34. 

* Beitrage zur Meeresfauna der Insel Mauritius. 

Zoologist, June 1859, pp. 6580-6584. 


its ckws and held it against the shell " for the space 
of ten minutes at a time, until fairly attached by a 
good strong base." ' This fact seems to indicate that 
the crab detaches and refixes its anemone when it 
changes its shell in the course of growth. Eomanes, 
however, quotes from Dr. E. Ball * the statement ' that 
when the common Sagartia parasitica is attached to a 
stone, and a hermit crab is placed in its vicinity, the 
anemone will leave the stone and attach itself to the 
hermit's shell.' 

Mr. Garstang tells me that at Plymouth there are 
two species of hermit crab associated with two distinct 
species of anemone : the Pagurussmd Actinia mentioned 
on p. 202, and P. bernhardus, which bears Adamsia 
Rondeletii. He finds that hermit crabs are eaten with 
great relish by fish ; they are, in fact, much used as 
bait by fishermen. Hence the association with the 
inedible Actinians must be of great service. When 
the hermit crabs are young and small they are obliged 
to live in shells without anemones, and Mr. Garstang 
has often found them, shells and all, in the stomachs 
of gurnards and other fish. He has never found the 
larger crabs with shells suited for Actinians in the 
stomachs of fish. 

Another hermit crab at Plymouth (Pagurus cua- 
nensis) is always found in shells covered with a bright 
orange-red sponge (Suberites domuncula). Mr. Gar- 
stang finds that sponges are intensely disliked by fish ; 

1 Critic, March 24, 1860. 


the smell alone is generally sufficient to repel them. 
Many Crustacea are known to live in the canal systems 
of sponges, and are thus protected. The significance 
of this association is to be found in the fact that 
Crustacea are the animals most relished and sought 
after by fishes, and that sponges are extremely re- 
pugnant to the latter. 

Such cases as these are some indication of the 
severity of the struggle for existence among marine 
forms of life. Very interesting evidence of this is to 
be found in Bateson's notes on the protective habits 
of shrimps and prawns. 1 He states that the wrasse 
will find a shrimp if the least bit be exposed, in spite 
of its protective colouration. If, however, ' the sand be 
fine, a shrimp will bury itself absolutely.' We can 
well understand the immense advantage which would 
be gained by a much persecuted crustacean if it 
associated with some animal repugnant to its foes. 

Colours and markings which direct the attention of an 
enemy to some non-vital part, but which are not 
attended by unpleasant qualities 

From cases such as those which have been just 
described we pass, by a very natural transition, to 
colours and markings which attract the attention 
of an enemy to some non-vital part after the animal 

1 Journ. Mar. Biol. Ass., New Series, vol. i. no. 2, Oct. 1889, pp. 
211 et seq. 


has been discovered. The part seized by the enemy 
breaks away, and thus gives the animal another chance 
of escape. The cases differ, however, from the pre- 
ceding ones in that the enemy is in no way injured 
by its mistake. In correspondence with this difference 
such features are associated with Protective Kesem- 
blances leading to concealment, and are not them- 
selves highly conspicuous, or are only conspicuous 
when the animal is thoroughly on the alert. The 
object of these characters is to direct attack to some 
unimportant part after all other methods of defence 
have failed, after disguise has been penetrated or 
speed surpassed. 

This is probably one of the meanings of the 
brightly-coloured wings of butterflies, in addition to 
their more obvious use in courtship. When the insect 
is flying they form a conspicuous mark easily seized 
by an enemy, and yet readily tearing without much 
injury to the insect. On this account we generally 
find the wings torn and notched when an insect has 
been long on the wing. 

In the spring of 1888 I caught a large number of 
Clouded Yellow Butterflies (Colias edusa) in Madeira. 
The limited number of species in the island (there 
are only about a dozen), and the abundance of 
small omnivorous lizards and of insect-eating birds, 
lead to the keenest pursuit of the butterflies, and I 
noticed that the hind wings of a considerable pro- 
portion of the Clouded Yellows were notched just 


behind the body. The notches generally corresponded 
on both hind wings, the insect having been seized at 
the instant when the wings came together in flight, 
or during one of its short pauses upon a flower. From 
the position of the injury it is clear that the enemies 
were aware of the situation of the body and attempted 
to seize it, but that they had been frustrated by the 
swift and wary butterfly with its bright yellow wings 
extending behind the short body, and offering an 
apparently convenient point for seizure. 1 

The bright yellow black-bordered under wings of 
the moths of the genus Tryphcena (Yellow Underwings) 
also possess this among their other meanings, as Mr. 
Jenner Weir has pointed out : they are exposed during 
flight, and their colours are far brighter than any other 
part of the insect. It is also very common to find the 
margin of these wings notched in captured specimens, 
and this is often the case when all other parts are fresh 
and perfect. The red and black under wings of the 
genus Catocala (including the Bed and Crimson 
Underwings) are perhaps useful in the same way. 

A still more interesting and obvious character of 
this kind is to be found in markings which actually 
suggest the presence of a vital part, such as an enemy 
would be likely to seize. On one occasion I intro- 

1 Skertchly has found such mutilations not uncommon among 
Bornean butterflies : he also notices the correspondence of the injury 
on the two sides. The wings are not torn in this way by flying 
through thick branches ; Skertchly states that even the most fragile 
butterflies can pass unharmed through dense undergrowth. 


duced a Small Heath Butterfly (Coenonympha pam- 
philus) into a lizard's cage. It was at once obvious 
that the lizard was greatly interested in the large eye- 
like mark on the under side of the fore wing: it 
examined this mark intently, and several times at- 
tempted to seize the butterfly at this spot. The 
observation seems to point to, at any rate, one use of 
the eye-like markings which are common on the 
under sides of the wings of butterflies. 

A very perfect and elaborate example of the same 
kind is witnessed in the Hair streak Butterflies (Thecla). 
Each hind wing in these butterflies is furnished with 
a ' tail,' which in certain species is long, thin, and 
apparently knobbed at the end. When the butterfly 
is resting on a flower the wings are closed and the 
hind wings are kept in constant motion, so that the 
' tails ' continually pass and re-pass each other. This 
movement, together with their appearance, causes the 
' tails ' to bear the strongest likeness to the antennae 
of a butterfly ; the real antennae being held so as not 
to attract attention. Close to the base of the supposed 
antennae an eye-like mark, in the most appropriate 
position, exists in many species. The effect of the 
marking and movement is to produce the deceptive 
appearance of a head at the wrong end of the body. 
The body is short and does not extend as far as the 
supposed head, so that the insect is uninjured when 
it is seized. 

This interesting fact of the resemblance of the 


tails and adjacent parts to a head in Thecla has been 
long known : it was first observed by Dr. Arnold in 
the case of a foreign species (Thecla larbas), and was 
confirmed by Dr. Forsstrona in other species. The 
fact is quoted by Kirby and Spence under ' Means of 
Defence of Insects,' but the interpretation offered, that 
the insects ' perhaps thus perplex or alarm their 
assailants,' hardly expresses the true significance of 
the character. 1 

The same fact was independently discovered by 
Mr. E. C. L. Perkins in 1888, and this keen naturalist 
at once perceived the meaning of the character to 
divert the attention of an enemy towards a non-vital 
part. The discovery is of especial interest because it 
was made upon an English species (Thecla W-album), 
and because Mr. Perkins tested his explanation by 
finding that this part had been torn in a considerable 
proportion of the butterflies. 

The observation renders it extremely probable 
that the slender ' tails ' which occur in the same 
position in many ' Blues ' (Polyommatus), and the 
bright colours and eye-like spots which are often 
associated with them, have a similar meaning. The 
'Blues,' when resting on a flower, have the same 
habit of moving the hind wings, as I have often ob- 
served in our common English species which are 
without ' tails.' The movement is such as would 
render the ' tails ' prominent and antenna-like if 

1 Kirby and Spence, People's Edition, 1867, p. 423. 


they were present ; and it may, therefore, have per- 
sisted from a time when the butterflies possessed these 
appendages. . 

Similar features in Reptiles 

A similar interpretation applies to the tails of 
lizards, which break off the instant an attempt is 
made to capture the animal by seizing this part. The 
tail is, of course, the first part which the pursuer has 
the chance of seizing. The great length of the tail, 
and the rapidity with which it is renewed after being 
shed, also support this interpretation. 

Similar features in Mammals 

It is very possible that the well-known peculiarity 
of the tail of the dormouse is to be explained in the 
same manner. The large bushy tail of the squirrel 
may possess a similar meaning (among others), for an 
enemy in pursuit would be liable to get only a mouthful 
of fur. In the north of Europe the squirrels which 
frequent the birches are black, while those on the 
pines are brown : both varieties, which are probably 
protective, become greyish in winter, and thus har- 
monise with the frosted bark. But the tails of both 
retain their summer colour, and would be thus more 
conspicuous. This fact was pointed out to me by my 
friend Mr. H. Balfour. 1 

1 On the other hand a seasonal change in the colour of the tail 


Similar features in Mollusca 

Semper ' has shown that certain freely exposed 
and active snails in the Philippines (Helicarion) have 
the same power of readily parting with their tails, 
and this is also true of a snail in the West Indies 
(Stenopus). The tail, or rather hinder part of the foot, 
which the animal sheds when it is seized and after- 
wards renews, is more conspicuous than the rest of the 
body. Semper found that the tails had been shed in 
about ten per cent, of the individuals of a species 
(Helicarion gutta) very common in the north-east of 

Recognition Markings 

A special kind of marking is often of great value 
in attracting the attention of individuals of the same 
species, instead of attracting the attention of enemies. 
From its obvious relation to the latter form of marking 
it is best included under the division of Warning 
Colours. Mr. A. E. Wallace has directed attention 
to the importance of Eecognition Markings, and an 
account of them will be found in his recently published 

seems to be not uncommon in certain localities in this country. The 
tail becomes cream-coloured at the end of summer, but resumes its 
ordinary appearance at the beginning of winter. Smaller differences 
appear to be general, the summer fur on the tail being coarser and 
more uniformly red than the winter fur. Bell's British Quadrupeds, 
2nd edition, p. 279. 

1 Semper : Animal Life, International Scientific Series, pp. 395 


volume, ' Darwinism ' (pp. 217-27) - 1 Such characters 
may be of use in aiding a species to escape from its 
enemies. Thus gregarious mammals, ' while they keep 
together, are generally safe from attack, but a solitary 
straggler becomes an easy prey to the enemy ; it is 
therefore of the highest importance that in such a 
case the wanderer should have every facility for dis- 
covering its companions with certainty at any distance 
within the range of vision ' (loc. cit. p. 217). Kecog- 
nition Markings would be especially useful * at a dis- 
tance or during rapid motion in the dusk of twilight, 
or in partial cover.' 

Recognition Markings in Mammals 

A very beautiful and familiar illustration is given 
by Mr. Wallace the white upturned tail of the rabbit, 
by which the young and inexperienced, or the least 
wary individuals, are shown the way to the burrow by 
those in front. It is very interesting to compare this 
marking with that of the skunk, which has been al- 
ready described as possessing a very conspicuous white 
tail. In the latter case the tail is held so that the 
slow-moving animal is always conspicuous, and appeals 
to the imagination and memory of its enemies ; the 
tail of the rabbit only becomes conspicuous when it is 
needed by other individuals of the same species, and 

1 The principle of Recognition Markings is set forth in a work by 
the late Alfred Tylor, Colouration in Animals and Plants, 1886, 
p. 30. 


when the animal is already alarmed and in full retreat 
for a place of security. 

In this way Mr. Wallace explains the conspicuous 
markings often present on gregarious ruminants, 
which are nevertheless protectively coloured in other 
respects. The remarkable differences in the length 
and form of the horns of different species are explained 
in a similar manner. 

Recognition Markings in Birds 

Mr. Wallace also shows that such characters are 
especially numerous and suggestive among birds. 
' Recognition Marks during flight are very important 
for all birds which congregate in flocks or which 
migrate together ; and it is essential that, while being 
as conspicuous as possible, the marks shall not inter- 
fere with the general protective tints of the species 
when at rest. Hence they usually consist of well- 
contrasted markings on the wings and tail, which are 
concealed during repose, but become fully visible 
when the bird takes flight ' (loc. cit. p. 222). 

Recognition of Birds' eggs may be aided by variation 
in certain species 

It is very probable that the great variation in the 
colours and markings of birds' eggs, which are laid 
close together in immense numbers, may possess this 


significance, enabling each bird to know its own eggs. 
I owe this suggestive interpretation to my friend 
Mr. Francis Gotch : it is greatly to be hoped that 
experimental confirmation may be forthcoming. The 
suggestion could be easily tested by altering the 
positions of the eggs and modifying their appearance 
by painting. Mr. Gotch's hypothesis was framed 
after seeing a large number of the eggs of the guillemot 
in their natural surroundings. It appears to be a 
more feasible explanation than that offered by Mr. 
Wallace. ' The wonderful range of colour and marking 
in the eggs of the guillemot may be imputed to the 
inaccessible rocks on which it breeds, giving it com- 
plete protection from enemies ' (loc. cit. p. 214). 

Recognition Markings in Insects 

Turning to insects, I do not believe with Mr. 
Wallace that colours and markings generally are to 
be explained in this way, although many instances 
of undoubted recognition characters will probably be 
found among them. In fact, a very interesting 
example only recently came before me. 

It has been already mentioned that Lepidopterous 
larvaB are especially subject to the attacks of parasitic 
insects (Hymenoptera and Diptera), which lay their 
eggs in or upon them. It is of the highest importance 
for a parasite to know whether a larva is already 
* occupied,' and also to ensure that other parasites 


shall recognise and avoid the larvae in which it has 
laid its eggs. When the eggs are laid within the body 
of a caterpillar the skin is pierced, and a small amount 
of blood exudes and generally forms a black clot. 
These black spots are probably recognised by other 
parasites, and the larva is consequently avoided. 
Although the spots would disappear after a change of 
skin, the parasites generally lay their eggs at about 
the same period of larval growth, and would be 
warned over a considerable part of this period. Al- 
though these are not, properly speaking, Eecognition 
Markings, we shall see that they form the foundation 
on which such characters have arisen. 

Other parasites (among the Hymenoptera), such as 
those of the genus Paniscus, lay eggs upon the body of 
their prey. The eggs are pear-shaped, and are firmly 
fixed by the stalk, which is knobbed at the end. So 
tightly do the eggs adhere that the caterpillar can change 
its skin without removing them (see pp. 275-77). 
Several eggs are fixed upon a large caterpillar, two 
or three upon a small one, although the number varies 
greatly in different individuals. 

These external eggs are black and shining, and 
they are very conspicuous against the colour of the 
caterpillar, which is generally green. When Professor 
Weismann was staying with me in the summer of 
1887, 1 showed him a larva of the Puss Moth (Cerura 
vinuLa) to which several eggs were attached. This led 
to a discussion as to the meaning of the colour, in 


the course of which we both independently arrived at 
the opinion that it is adapted to serve as a warning 
to other parasites that the larva is already ' occupied.' 
The eggs, being black, somewhat resemble the scars 
caused by the introduction of internal eggs, so that 
the species which deposit such eggs may be warned 
off, as well as those of the genus Paniscus. 




WE now approach one of the most interesting aspects 
of our subject, and one that has played an important 
part in the history of evolution and of natural 

History of the subject 

The fact that certain butterflies belonging to 
widely separate groups, but inhabiting the same 
localities, possess the most remarkable superficial 
resemblance, has been known for a very long time. 
An interesting quotation from Boisduval's ' Species 
General des Lepidopteres ' (pp. 372, 373) is given by 
Mr. Eoland Trimen at the head of his paper on 
Mimicry among African butterflies. 1 Boisduval's sen- 
tence, written in 1836, refers to an African Swallow-, 
tailed Butterfly, which still remains the most remark- 
able instance of Mimicry known in the _worldl 
' C'est une chose bien remarquable que de voir la nature 
creer a cote les uns des autres 1' Euplcea Niavius, le 

1 Linn. Soc. Trans, xxvi. p. 497. 


Diadema dubia, et le Papilio Westermanni, trois 
Lepidopteres qui se ressemblent presque completement 
par le port, le dessin, et la couleur, quoique apparte- 
nant a des genres fort eloignes et de tribus differentes.' 

From 1836, and the even earlier dates at which 
these remarkable resemblances had been noticed, 
until 1862, no attempt at explanation had been made ; 
but in that year Mr. Bates's classical paper appeared. 1 
In this admirable~essay the author showed the advan- 
tage which must necessarily be gained by a palatable 
form, hard pressed by enemies, if it sheltered itself 
under the reputation of some conspicuous species 
well known to be inedible. 

Only three years before, Darwin, writing to 
Asa Gray, had said : ' I cannot possibly believe that a 
false theory would explain so many classes of facts as 
I think it certainly does explain. On these grounds 
I drop my anchor, and believe that the difficulties will 
slowly disappear.' 2 One great difficulty which had 
so long been a puzzle to naturalists was therefore 
satisfactorily explained by the new theory, within a 
few years of Darwin's prediction. 

It is most delightful to read of the interest and 
enthusiasm with which Bates's paper was received by 
Darwin. ' In my opinion it is one of the most re- 
markable and admirable papers I ever read in my 

1 Contributions to an Insect Fauna of the Amazons Valley. 
Linn. Soc. Trans, vol. xxiii. 

2 Life and Letters, vol. ii. p. 217. 


life,' he writes. ' I am rejoiced that I passed over the 
whole subject in the " Origin," for I should have made 
a precious mess of it. You have most clearly stated 
and solved a most wonderful problem. Your paper 
is too good to be largely appreciated by the mob of 
naturalists without souls ; but rely on it that it will 
have lasting value, and I cordially congratulate you 
on your first great work.' * This was Darwin's opinion 
of a theory which is often lightly criticised or even con- 
demned by many biologists who offer nothing in its 

The relation of the theory of Mimicry to Evolution 

Mr. Bates's paper afforded a twofold support to the 
arguments in the ' Origin of Species,' at a very criti- 
cal time in the history of these opinions. In the 
first place it showed that an important class of facts 
was unintelligible upon any theory except that of 
evolution. The proof of this is best given in Dar- 
win's own words, also quoted by Mr. Francis Darwin. 2 
'By what means, it may be asked, have so many 
butterflies of the Amazonian region acquired then- 
deceptive dress ? Most naturalists will answer that 
they were thus clothed from the hour of their creation 
an answer which will generally be so far triumph- 
ant that it can be met only by long-drawn argu- 
ments ; but it is made at the expense of putting an 

1 Life and Letters, vol. ii. pp. 391-93. 
1 Ibid., vol ii. pp. 391-92. 


effectual bar to all further inquiry. In this particular 
case, moreover, the creationist will meet with special 
difficulties; for many of the mimicking forms of 
Leptalis can be shown by a graduated series to be 
merely varieties of one species ; other mimickers are 
undoubtedly distinct species, or even distinct genera. 
So again, some of the mimicked forms can be shown to 
be merely varieties, but the greater number must be 
ranked as distinct species. Hence the creationist will 
have to admit that some of these forms have become 
imitatory by means of the laws of variation, whilst 
others he must look at as separately created under 
their present guise ; he will further have to admit 
that some have been created in imitation of forms 
not themselves created as we now see them, but due 
to the laws of variation ! Professor Agassiz, indeed, 
would think nothing of this difficulty ; for he believes 
that not only each species and each variety, but that 
groups of individuals, though identically the same, 
when inhabiting distinct countries, have been all 
separately created in due proportional numbers to the 
wants of each land. Not many naturalists will be 
content thus to believe that varieties and individuals 
have been turned out all ready made, almost as a 
manufacturer turns out toys, according to the tempo- 
rary demand of the market.' l 

But Mr. Bates's theory was equally important in 

1 From a review of Bates's paper by Charles Darwin. Natural 
History Revieiv, 1863, p. 219. 


another respect. It not only supported the doctrine of 
evolution, but it afforded strong confirmation of the 
theory of natural selection, by which Darwin explained 
how it was that evolution took place. Every step in 
the gradually increasing change of the mimicking in 
the direction of specially protected form, would have 
been an advantage in the struggle for existence, while 
the elements out of which the resemblance was built 
exist in the individual variability of the species, a 
variability which is hereditary. 

The transition from Warning to Mimetic appearances 

It will have been observed that Mimicry has already 
been mentioned in the pages on Warning Colours, and 
that a gradual transition may be traced from the one 
principle to the other. And yet Mimicry itself was 
explained long before many of the conclusions con- 
cerning Warning Colours which have been described. 
In this, as in so many other cases, the steps by which 
the subject is best approached are almost exactly oppo- 
site to the historical steps by which it was gradually 

The transition from warning to mimetic forms 
may be shortly recapitulated. 

1. The existence of Warning colours, attitudes, &c. 
in species which possess some quality unpleasant to the 
enemies of their class : recognised by Bates in butter- 
flies which are mimicked by others (loc. cit. 1862) ; the 


principle especially supported and extended by Wal- 
lace; also greatly supported by Trimen, Belt, and 
many others. 

2. The tendency for the species in each specially 
protected group of butterflies to resemble each other 
(by convergence or arrested divergence) more closely 
than those in other groups not similarly protected, 
thus suffering a smaller amount of destruction while 
their enemies are being educated to avoid them ; sug- 
gested by Meldola (' Ann. and Mag. Nat. Hist.' Dec. 
1882) as an extension of the principle discovered by 
Fritz Miiller and described in the next paragraph. 

3. The tendency for the members of distantly re- 
lated groups of specially protected butterflies to resemble 
each other, thus gaining the advantages described 
above : discovered by Fritz Miiller (' Proc. Ent. Soc. 
Lond.' 1879, p. xx.). The fact of the resemblance was 
first observed by Bates (loc. cit.). 

4. An extension of the same principle to all the 
groups of such specially protected animals : in these 
the same colours and patterns occur again and again, 
and advantage is gained by the fact that the types of 
appearance are those which produce most effect upon 
the sight of an enemy, as well as by the fact that only 
a few different types have to be learnt. Certain types 
of colour and pattern are eminently advantageous for 
animals in which the special protection is imperfect, 
because they are so thoroughly advertised by other 
animals in which the protection is complete and 



inspires great dread (Poulton, Proc. Zool. Soc.' 
March 1887). 

5. The latter cases naturally lead to those of 
true Mimicry, in which a group of animals in the 
same habitat, characterised by a certain type of colour 
and pattern, are in part specially protected to an 
eminent degree (the mimicked), and in part entirely 
without the special protection (the mimickers), so that 
the latter live entirely upon the reputation of the 
former. Discovered by Bates in Tropical America, 
(loc. cit. 1862), then by Wallace in Tropical Asia and 
Malaya (loc. cit. 1866), and by Trinien in South Africa 
(loc. cit. 1870). 

Cases to which the term Mimicry is best applied 

The term Protective Mimicry is best applied to the 
deceptive appearance of the unprotected forms in the 
last class only. Instances of such true Mimicry, in 
which the resemblance deceptively suggests the pre- 
sence of some positively unpleasant quality, are so 
common and striking that we need some name for 
them ; and it is in every way best to retain the 
historic term. An additional advantage is that the 
word Mimicry implies the deception and unreality 
which is so obvious in the last class of cases de- 
scribed above. For this reason it is best to include 
all the other classes and the protected forms in the 
fifth class, unc|er Warning Colours ; for their object 


is to warn an enemy, as effectually as possible, of 
real danger or unpleasantness ; while the object of 
the unprotected forms in the fifth class is to suggest 
the presence of some unpleasant attribute which has 
no existence in fact. 

The transition from Warning to Mimetic colours 
which occurs in the fourth class is no objection to 
this arrangement ; for we cannot escape transition in 
any classification of the uses of colour in animals. 
Some authorities have failed to make any distinction 
between Mimicry and the other forms of Protective and 
Aggressive Resemblance ; but such an arrangement 
would confound together cases in which appearance is 
used for concealment, and those in which it is made 
use of in order to attract attention. 1 

1 S. B. J. Skertchly has recently (Ann. and Mag. Nat. Hist., Series 
vi. vol. iii. pp. 477 et aeq.) urged (a) that 'protective resemblance 
copies stationary objects, mimicry simulates moving ones.' He accord- 
ingly maintains that the former is a defence against enemies which 
attack butterflies at rest, the latter against those which attack them 
on the wing. He further argues that the attacks of birds constitute 
the only real danger to an insect on the wing ; (6) that certain ob- 
servers (Skertchly, Pryer, Scudder) agree in considering these attacks 
to be of very little importance ; and (c) that therefore Mimicry, to- 
gether with the shyness of moving objects exhibited by all butterflies 
on the wing, ' are habits acquired long since, which have survived the 
necessity that gave them birth.' He maintains that this argument 
is supported by (d) the ' law that the amount of apprehended danger 
is measurable by the efforts taken to avoid it,' inasmuch as ex- 
amples of Mimicry are far rarer than examples of Protective Resem- 

To this^e may reply: (a) the alleged contrast between Pro- 
tective Resemblance and Mimicry is only a usual consequence of the 
real difference between them (see pp. 222-23, also p. 71). Further- 


Convenience of the term Mimicry 

Mr. Bates's term has been criticised because it is 
generally used to describe voluntary actions, whereas 
the Mimicry alluded to in these pages is of course un- 
conscious, and has been gradually produced by the 
operation of natural selection. 1 This use of the word 

more, the alleged contrast frequently breaks down ; thus, a dead leaf 
driven by the wind (see p. 56), or a piece of stick swinging by a thread, 
are not uncommonly resembled ; while the conspicuous appearance of 
Mimetic and Warning Colours are most certainly of value during rest 
as well as during flight (see pp. 189-95). Against the evidence offered 
by Skertchly (b) may be put the observations of other naturalists 
(see pp. 228-30; many other examples might have been recorded). We 
must also remember that very little of the destruction of life which 
we know takes place is actually witnessed by us. Against (c) may 
be urged the fact that characters begin to decline directly they be- 
come useless, while certain mimetic resemblances are perhaps more 
wonderfully elaborate and perfect than anything else in the animal 
kingdom. Every naturalist will agree with (d), but it is really de- 
structive of the argument based upon it. The danger to most 
mimetic species must indeed be great if measured by the efforts taken 
to avoid it. Some of the marvellous results of such ' efforts ' are de- 
scribed in this volume. Skertchly's argument only applies to the 
numerical ratio between the examples of Mimicry and Protective 
Resemblance ; and this ratio is readily explicable on other grounds. It 
has been shown that Warning Colours can only be adopted safely by a 
small proportion of the insect fauna in any country (see pp. 178-80), 
and also that mimetic individuals must be far rarer than the nauseous 
forms they resemble (see pp. 243-44 ; see also p. 231). 

1 After this sentence had been printed I came across a most 
extraordinary statement of the theory of Mimicry by Skertchly, I.e. 
This theory ' presupposes (a) that danger is universal ; (b) that some 
butterflies escape danger by secreting a nauseous fluid ; (c) that other 
butterflies noticed this immunity ; (d) that they copied it.' The opinions 
expressed in the words I have italicised will hardly be accepted by a 


is, however, well known, and is not likely to mislead 
anyone ; and in addition to its historical accuracy the 
word is more convenient than any other, as Mr. 
Wallace has pointed out. Thus we obtain the con- 
venient series of words mimic, mimicry, mimetic, 
mimicker, mimicked, mimicking. 

Various degrees of affinity between mimicking and 
mimicked species 

The various examples of Mimicry may be divided 
according to the affinity of the forms which resemble 
each other. Thus a species may mimic another closely 
allied species, or one of a widely separated family, of a 
distinct order, class, or even sub-kingdom. Mr. Bates 
first explained the Mimicry of butterflies and moths, 
so that in this case the divergence between the species, 
although generally very great, is not nearly so large 
as that of other examples. The former, however, in- 
cludes some of the most striking examples known, 
and will be first described. 

The Butterflies which afford models for Mimicry 

In giving some account of Mimicry among butter- 
flies, it is first necessary to speak of the models which 
are most generally copied in all the warmer parts of 

single naturalist. I imagine that even the American Neo-Lamarckians 
do not follow their founder so far as to believe that the volition of an 
animal could account for all the details of mimetic resemblance. 


the world. These models almost invariably belong 'to 
the two great families Danaidce (including Euploea, 
Danais, and Hestia) and Acrceidce, while the Heliconidte 
of Tropical America are also mimicked. It has been 
already pointed out that the Danaida, which inhabit 
the region of which the Heliconidce are characteristic, 
have adopted the appearance of the latter, and may 
therefore be called Heliconoid Danaidce. 1 

Proof that the mimicked Butterflies are specially pro- 
tected by a nauseous taste or smell 

It is of the greatest importance to prove that these 
butterflies are specially protected in some unusual and 
exceptionally complete manner, so that resemblance 
to them would be advantageous. All observers speak 
of their slow flight, gaudy colours, and abundance. 
Thus Mr. Trimen's descriptions of the Danaidce and 
Acrceidce are equally true of the Heliconidce, and of all 
other butterflies or moths which are the objects of 
Mimicry. ' The slow flight, the conspicuous colours, 
the complete disregard of concealment, no less than 
the great abundance of individuals, are characteristics 
indicating unmistakably that these butterflies are 
favoured races, enjoying advantages and immunities 
above their fellows.' 2 The colours of the under sides 

1 Bates called them ' Danaoid Heliconidce,' but Trimen pointed 
out that the transposed words more truly express the relationship 
(loc. cit. p. 499). 

2 Loc. cit. p. 498. 


of the wings are the same as those of the upper sides, 
or at any rate are equally conspicuous. A peculiar and 
frequently unpleasant smell has been noticed by all 
observers who have studied these groups. It is pro- 
bable that the same means of defence is present in the 
other stages, and this has been proved in certain 
cases (e.g. Acraa horta, Trimen). The unpleasant 
smell frequently resides in a clear yellow fluid which 
exudes on the slightest pressure. 

Mr. Trimen l has also called attention to the fact 
that the conspicuous butterflies and moths which 
possess such qualities have a remarkably elastic struc- 
ture, and can endure very severe pressure without 
injury. The wings are so flexible that they can be 
bent and distorted without breaking the nervures. 
The insects can in this way often recover from the 
mistaken attacks of insect-eating animals. Skertchly 
also maintains, from his experience in Borneo, that 
nauseous properties are accompanied by strong 

There is, unfortunately, too little direct experi- 
mental proof of the unpalatability of the specially 
protected groups which are the chief models of Mimi 
cry. When, however, all the observations are brought 
together they constitute a fair amount of evidence, 
and there can be no doubt about the results of future 

Mr. Bates mentions the glands near the anus 

1 Loc. cit. pp. 498, 499. 


of certain Heliconid<z, and he noticed that they all 
possess a peculiar smell. Neither Bates nor Wallace 
saw them attacked by birds, dragon-flies, lizards, or 
predaceous flies (Asilid<z) y although all these devour 
other butterflies, and the Heliconida, from their abun- 
dant flocks and slow flight, would be a particularly 
easy prey. 1 

In Brazil and in Nicaragua some important obser- 
vations upon the Heliconidce (probably including the 
Danaidce) were made by Mr. Belt. He says : ' I have 
seen even spiders drop them out of their webs again ; 
and small monkeys, which are extremely fond of 
insects, will not eat them, as I have proved over and 
over again.' * ' I observed a pair of birds that were 
bringing butterflies and dragon-flies to their young, 
and although the Heliconii swarmed in the neighbour- 
hood, and are of weak flight so as to be easily caught, 
the birds never brought one to their nest.' A tame 
white- faced monkey ' would greedily munch up beetle 
or butterfly given to him, and I used to bring to him 
any insects that I found imitated by others, to see 
whether they were distasteful or not. I found he 
would never eat the Heliconii. He was too polite not to 
take them when they were offered to him, and would 
sometimes smell them, but invariably rolled them up 
in his hand and dropped them quietly again after a 
few moments. There could be no doubt, however, 

1 Loc. cit. p. 510 ; Darwinism, p. 234. 
1 Naturalist in Nicaragua, p. 109. 


from the monkey's actions, that they were distasteful 
to him.' 1 

Mr. Belt, however, observed that a yellow and 
black wasp caught these butterflies to store up in its 
nest, and that the Heliconida were very wary when 
the wasp was near, although quite fearless in the 
presence of other enemies. They were also attacked 
by a flower-haunting spider. These exceptions are 
very interesting, because the unpleasant qualities of 
such specially defended groups generally appeal with 
success to the taste of animals from the most widely- 
separated places in the animal kingdom. When certain 
enemies are thus careless of the qualities which inspire 
such general respect, it is probable that we witness a 
result brought about in the first instance by the 
excessive competition for food. In times of scarcity, 
an^ individuals of a species which were able to 
disregard the unpleasant taste, would be likely to 
predominate over those with more delicate gustatory 

From Africa, Mr. Trimen quotes an observation of 
Mr. Bowker upon a small Kaffrarian lizard which 
pursues a peculiarly wary butterfly with the greatest 
energy and persistence, while it neglects the inert and 
abundant Acr&idce. Mr. Trimen has made similar 
observations with regard to dragon-flies and Mantida, 
both of which feed largely on butterflies, but were 
never seen to touch an Acrcea or Danais.* 

1 Loc. cit. pp. 316, 317. Loc. cit. p. 500. 


In India, on the other hand, M. de Niceville found 
that Acrcea viola was the only butterfly refused by all 
the species of Mantis with which he experimented. Mr. 
Wallace quotes an observation by the Hon. Justice 
Newton, upon the bulbul, which chases and greedily 
devours a swift but palatable butterfly, but could only 
be induced to touch a Danais by repeated persecution. 1 

Some very interesting observations prove that the 
unpleasant qualities are retained in the dried specimens 
long after death. ' Mr. Bates observed that, when 
set out to dry, specimens of Heliconidce were less 
subject to the attacks of vermin ; ' 2 while Professor 
Meldola even found that ' in an old collection which 
had been destroyed by mites, the least mutilated 
specimens were species of Danais and Euplcea.' 3 This 
observation has been confirmed by Mr. J. Jenner 

Conclusion warranted by the evidence 

I have brought together all the available evidence 
on this subject, because there has been of late years 
a rather wide-spread tendency to reject the explana- 
tion offered by Mr. Bates. The evidence, however, 
certainly warrants the conviction that experiment 
would prove all (protectively) mimicked species to be in 
some way disagreeable or even dangerous to the enemies 
of their class ; and if this be so, the probability that 

1 Darwinism, p. 235. 2 Darwinism, p. 234. 

Proc. Ent. Soc. Land. 1877, p. xii. 


all mimetic resemblances are due to natural selection 
contrasts in the strongest manner with the entire 
absence of any alternative theory on the part of Mr. 
Bates's critics. 

Conditions under which Protective Mimicry occurs 

The conditions under which Mimicry occurs also 
strongly confirm the view that these resemblances 
have been produced by the operation of natural selec- 
tion. These conditions have been found to be very 
nearly constant by every naturalist who has published 
any observations on the subject. They have recently 
been very concisely stated by Mr. Wallace as fol- 
lows. 1 

* 1. That the imitative species occur in the same 
area and occupy the same station as the imitated. 

4 2. That the imitators are always the more de- 

' 3. That the imitators are always less numerous 
in individuals. 

5 4. That the imitators differ from the bulk of 
then-, allies. 

4 5. That the imitation, however minute, is external 
and visible only, never extending to internal characters 
or to such as do not affect the external appearance.' 

1 Darwinism, pp. 264. 265. 


Mimicry in the Butterflies of Tropical America 

The Heliconidce, and Danaida which resemble them, 
in Tropical America, are chiefly mimicked by Pierida 
the family of ' Whites ' to which our common 
Cabbage Butterflies or Garden Whites belong. 
Mr. Bates figures one non-mimetic species of the 
family, and the resemblance to our familiar butter- 
flies, together with the immense difference between 
it and the mimetic Pierida in the same country, are 
very striking. He also figures many beautiful 
examples of Mimicry, and the two plates should be 
studied by anyone who can obtain access to Vol. xxiii. 
of the ' Transactions of the Linnean Society ' (pp. 
495-566). One of the most striking instances is 
reproduced in Mr. Wallace's recent work. 1 

Mr. Bates found that two different Heliconidce 
in two adjacent areas were in certain cases mimicked 
.by two varieties of the same species of Pierid, a fact 
which points to the comparatively recent origin of the 
resemblance ; for otherwise the two varieties would 
have had time to become distinct species. A similar 
fact was observed by Mr. Wallace in the Malay 

The specially protected forms were not only 
mimicked by Pieridce but by Swallow-tails (Papilio) 
and other butterflies, and in many cases by day-flying 
moths also. 

1 Loc. tit. p. 241. 


I have recently heard the objection raised to the 
theory of Mimicry, that non-mimetic Pieridce, with 
the typical appearance of their group, are among the 
commonest butterflies in South America. It is there- 
fore argued that the Pieridce are quite able to take 
care of themselves, and, if any of them resemble 
other forms, it cannot be in order to shelter them- 
selves under the reputation of the latter. There 
does not seem to be much force in this objection ; the 
forces which tend to the extermination of a species 
are so nicely balanced against the forces by which 
its existence is maintained, that a very minute and 
often quite inappreciable difference may lead to pre- 
dominance or to scarcity, perhaps ending in exter- 
mination. Because the typical Pieridce in South 
America appear to be predominant, it by no means 
follows that all the species of this group have always 
been so. Furthermore, the fact that all mimicking 
Pieridce are scarce, and that they invariably resemble 
the butterflies of specially protected groups which are 
also mimicked by other butterflies and by moths, is 
a practical and complete answer to the objection. 

Mimicry in Asiatic Butterflies 

In the Malayan islands and in India Mr. Wallace 1 
found that the Danaidce are the chief models for 
Mimicry, although certain Morphidce and one section 

1 Linn. Soc. Trans, vol. xxv. pp. 19-22. 


of Swallow-tailed Butterflies (Papilio) were also re- 
sembled. He gives a list of eighteen examples of 
mimetic resemblances from among the Swallow-tails 
alone. Among these was an interesting case in which 
the males of a Malayan species (Papilio paradoxd) 
mimicked the males of one Euplcea (E. Midamus), 
while the females mimicked the females of another 
Euplcea (E. Rhadamantlms). A. special section of 
Swallow-tails are also the objects of Mimicry in 
South America. 

The African Papilio merope as an example of Mimicry 

By far the most remarkable example of Mimicry 
is that alluded to in the passage quoted from Bois- 
duval, and which has been worked out, together with 
many other cases of Mimicry, by Mr. Roland Trimen 
in South Africa. This wonderful example does not 
appear to be sufficiently well known, although it is 
excellently described and illustrated in Mr. Trimen's 
paper, 1 from which this account and the figures upon 
the coloured plate are taken. Each of the figures 
has been reduced to half the natural size. 

2 Fig. 1 closely resembles the male, while fig. 2 re- 
presents the female, of a beautiful pale yellow and 
black Swallow-tailed" Butterfly (Papilio meriones) which 
is found in Madagascar. The only marked difference 
in colour between the sexes is the larger amount of 

1 Linn. Soc. Trans, vol. xxvi. pp. 497-522. 

* See the coloured plate at the beginning of the volume. 


black in the female. In Africa a Swallow-tailed 
Butterfly (Papilio merope) occurs, of which the male 
is represented in fig. 1 ; the female, on the other 
hand, is without the ' tails ' on the hind wings, and 
presents a totally different appearance from the male ; 
it occurs in three different varieties, each of which 
mimics a different species of Danais prevalent in its 

Fig. 3 A represents Danais echeria, a specially pro- 
tected butterfly, common in South Africa, and rendered 
conspicuous by light brown and white patches and spots 
upon a black ground. The appearance of the female 
P. merope (the P. cenea form) in the same locality is 
shown in fig. 3. It is very interesting to find that 
D. echeria is also mimicked by two other species of 
Swallow-tail and by another butterfly (Diadema mima). 
In Natal the ordinary form of the Danais is replaced 
by a variety in which the spots on the fore wings are 
white instead of ochreous. In Natal the female P. 
merope undergoes a corresponding change, and inter- 
mDdiate varieties of both mimic and mimicked are also 

The appearance of another unpalatable butterfly, 
Danais niavius, is shown in fig. 4A. This conspicuous 
black and white butterfly is abundant in tropical 
Western Africa, and it is very faithfully imitated by 
two other butterflies in the same locality, a Diadema 
and a form of the female of Papilio merope (the P. 
hippocoon form), shown in fig. 4. This is the ex- 


ample of Mimicry alluded to by Boisduval, although 
he uses different names for the butterflies. The 
Natal form of Danais niavius is rather different, 
having broader white markings, especially on the 
hind wings, and both its mimics have undergone a 
corresponding change in the . same locality. The 
Natal varieties are represented in figs. 4i and 4. It 
is very interesting to learn that the two varieties 
of P. merope which mimic the two species of Danais, 
although so widely different in appearance, are still 
connected by intermediate forms. 

A third species of Danais, the conspicuous black, 
reddish-brown, and white D. chrysippus, is extremely 
abundant and has a very wide range, occurring 
throughout Africa, in Southern Europe, Southern 
Asia, the Malay Archipelago, &c. This butterfly, 
represented in fig. 5A, is almost everywhere attended 
by its mimic, Diadema bolina, which occurs in two 
forms exactly resembling the two forms of the Danais. 
A third variety of the female P. merope (the P. tropho- 
nius form), shown in fig. 5, occurs in Cape Colony, 
and mimics Danais chrysippus. 

The female of P. merope also occurs as a fourth 
variety, unlike the others, but connected with the 
second of them by an intermediate form. Mr. Trimen 
considers that this variety ' is probably modified, or 
in course of modification, in mimicry of some other 
protected butterfly, possibly not a Danais.' 

To recapitulate this marvellous instance of the 
relations which may obtain between the organisms 


inhabiting the same land : Three well-known species 
of Danais occur in Africa, each of which is mimicked 
by a special variety of the female of Papilio merope ; 
two of the Danaidce present two varieties in the range 
over which they are accompanied by the P. merope, 
and some females of the latter undergo corresponding 
changes ; intermediate varieties occur and also connect 
one of these forms with a fourth variety of the female. 
Furthermore, in Madagascar, which in so many other 
instances furnishes us with a glimpse of what the 
ancestral African fauna must have been, a Papilio 
is still living with a male like that of P. merope, and 
having a female only differing in the rather greater 
predominance of dark markings, a predominance 
which is thus entirely in the direction of the far darker 
African females. 

It requires a very slight exercise of the imagina- 
tion to picture the steps by which these marvellous 
changes have been produced ; for here the new forms 
have arisen at so recent a date that many of the inter- 
mediate stages can still be seen, while the parent form 
has been preserved unchanged in a friendly land, where 
the keener struggle of continental areas is unknown. 1 

1 Since the appearance of Mr. Trimen's important paper, the 
interest and intricacy of the case have much increased. Mr. Mansel 
Weale (Trans. Ent. Soc. Land. 1874, pp. 131 et scq.) found a number 
of the larva feeding together in one locality, near King William's Town. 
From these he bred seven males, four females of the Cenea form, one 
of the Trophonius, and one of the Hippocoon form, thus confirming 
Mr. Trimen's original suggestion, that all these belong to the same 
species. The butterflies have furthermore been taken in coitu more 


Protective Mimicry more often found in female 
Butterflies than in males 

This example enforces a conclusion arrived at by 
the study of mimetic butterflies in all parts of the 

than once. Mr. Mansel Weale also points out that the sexes are 
remarkably different in their manner of flight. 

It is now admitted that the West African forms must be separated 
from the Southern as a distinct species. The western species is now 
called P. merope, while the name P. cenea is extended to cover all 
the varieties of the southern species. The males of the two species 
are very similar, but P. ccnea has somewhat shorter wings, shorter 
tails, &c. The female P. cenea presents all three varieties described 
above. The western females lack the Cenea form which mimics 
D. echeria ; and the Hippocoon form differs in its larger size and 
smaller extent of the white markings, especially on the hind wing, in 
these respects agreeing with the western form of D. niavius, which 
it mimics. It is interesting to note that the western Trophonius 
form, mimicking the small D. chrysippus, is little if at all larger than 
the corresponding form of the southern species. A third variety of 
the western female, the P. dionysos form, is of extreme interest, in 
that it combines the features of Hippocoon and Trophonius, and also 
indicates a transition towards the female P. meriones of Madagascar. 
Mr. Trimen also describes many varieties transitional between the 
three forms of the southern female. For further details and a 
thorough discussion of the whole question, consult Mr. Roland 
Trimen's South African Butterflies, vol. iii. 1889, pp. 243-55 ; also 
the same author in Trans. Ent. Soc. Lond. 1874, pp. 137 et seq. 

Two new species have also been added to the P. merope group. In 
the island of Grand Comoro, adjacent to Madagascar, another species, 
P. Humbloti, has been discovered. P. Humbloti somewhat resembles 
P. meriones, but the sexes are even more alike. The other species, 
P antinorii, has been found in Abyssinia, and is of extreme interest, 
in that the sexes are nearly alike, as in the island forms. It is much 
to be hoped that further research will bring to light the causes which 
have favoured the persistence of the ancient unmodified form in this 
one locality on the mainland of Africa. 

I wish to express my sincere thanks to Mr. Roland Trimen for 
kindly looking through the proofs and suggesting references. 


world that the females are far more liable to 
assume this method of defence than the males. Thus 
Mr. Wallace found that the eastern Morphidcs and 
the special group of Swallow-tails were only mimicked 
by the females of other Swallow-tails ; and similar 
facts have been observed in America. 

Mr. Wallace, in his paper on the Malayan Swallow- 
tails, explains the commoner mimetic resemblances of 
females, because ' their slower flight, when laden with 
eggs, and their exposure to attack while in the act 
of depositing their eggs upon the leaves, render it 
especially advantageous for them to have some addi- 
tional protection.' 

Mr. Belt adopts the same explanation, and also 
makes the very ingenious suggestion that, when the 
males have not been similarly modified, it is because 
of the preference of the more conservative sex for con- 
sorts which retain the ancestral colour of the group 
to which they belong. He points out that the males 
of many of the mimetic * Whites ' (Pierida) ' have the 
upper half of the lower wing of a pure white, whilst 
all the rest of the wings is barred and spotted with 
black, red, and yellow, like the species they mimic. 
The females have not this white patch, and the males 
usually conceal it by covering it with the upper wing, 
so that I cannot imagine its being of any other use 
to them excepting as an attraction in courtship, to 
exhibit to the females, and thus gratify a deep-seated 
preference for the normal colour of the order to which ' 


these mimetic forms belong. 1 Ingenious as this sug- 
gestion is, it needs confirmation by a care.ful observa- 
tion of the habits displayed during the courtship of 
these species. 

Protective Mimicry in Moths 

Certain conspicuous moths are also mimicked by 
other moths only distantly related to them. A good 
example was discovered at Amboyna by the naturalists 
of the ' Challenger ' expedition ; the figures are repro- 
duced by Mr. Wallace. 8 

Protective Mimicry in British Moths 

The only examples of mimicked species known 
in the British Lepidoptera occur among the moths. 
Mr. Wallace first called attention to the resem- 
blance of the female of the Muslin Moth (Diaphora 
mendica) to the far more abundant White Ermine 
Moth (Spilosoma menthastri), both species being white 
with black spots, and occurring at the same time of 
the year. The mimicked species has been proved to 
be unpalatable, while the fact that the male of the 
mimicker is dark coloured and well-concealed is evi- 
dence that the latter is palatable. The conclusion 
should, however, be confirmed experimentally, for, 
until the test has been applied, we cannot be sure that 
the case is one of true Mimicry rather than one of 

1 Loc. cit. pp. 384-85. 2 Darwinism, p. 247. 


resemblance between unpalatable forms, described 
under Warning Colours (see pp. 191-96). The close 
affinity between the two species, and their similarity 
to other closely related species, probably indicate that 
the resemblance is due to arrested divergence rather 
than convergence ; if so, the case before us is not a 
good and typical example of Mimicry. 

A similar objection holds against an example in 
which I have experimentally proved that the benefits 
of true Protective Mimicry are certainly conferred. I 
refer to the unpalatable and abundant white Satin 
Moth (Stilpnotia salicis), which is resembled by its 
near relative, the common white Gold Tail Moth 
(Porthesia auriflud). The abundance of the latter, 
and the affinity between the two species, make this 
instance a very bad one, but the experiments were most 
instructive, and indicate the benefits derived from 
Mimicry in a most suggestive manner. 

Experimental evidence of the protection afforded by 
mimetic resemblance 

I offered a Satin Moth to a marmoset which was 
excessively fond of insects, and which had not gratified 
this appetite for some days. He seized the moth, and 
ate it with the strongest expressions of disgust, well 
known to all who are acquainted with him ; in fact, 
had not the attempt been made to take the moth 
away, I believe that he would have rejected it. As 



soon as he had finished this nauseous morsel, I offered 
him a Gold Tail Moth, but he shrank from the sight of 
it, and had evidently had quite enough of white moths 
for the time being. And yet he eagerly seized and 
devoured many other inconspicuous insects which I 

FIG. 50. Satin Moth (to the left) and Gold Tall Moth on an ivy leaf ; 
natural ze. Although the moths are often of the same size, the 
Gold Tail is generally the smaller. 

offered to him. It was merely the resemblance to the 
moth which had so disgusted him that saved the Gold 
Tail, for on another occasion he ate four of these 
moths one after the other with the greatest relish. 
The marmoset has a far more delicate taste than any 


other insect-eating animal with which! am acquainted, 
and it appears therefore to be certain that the Gold 
Tail Moth is palatable. I have also confirmatory 
evidence as to both these species, from the behaviour 
of other animals. The great abundance of the Gold 
Tail, in spite of its agreeable taste, must be in part 
explained by the fact that the caterpillar is specially 
protected in different ways (see pp. 171-72), but it must 
also follow from the fact that white and conspicuous 
moths are generally unpalatable. The strong super- 
ficial resemblance between the two moths is shown in 
fig. 50. 

Mimicry may be a source of danger to the mimicked 

While the experiment with the marmoset illustrates 
the benefits conferred on the mimicker by the well- 
deserved reputation of the form it imitates, an experi- 
ment made by Professor Weismann proves that the 
safety of both may be endangered when the mimicker 
becomes relatively abundant. Professor Weismann 
found that the black and yellow caterpillars of the 
Cinnabar Moth (Euchelia jacobcece) were refused by 
the Green Lizard (Lacerta viridis) ; he then introduced 
some young caterpillars of the Fox Moth (Lasiocampa, 
rubi), which are very similar in appearance. The 
lizards first cautiously examined these larvae, and then 


ate them. After this they were seen to taste the 
Cinnabar caterpillars, in order to test whether they were 
really as unpalatable as they appeared to be. 1 

Further examples from the British Moths 

Professor Meldola has also suggested that three 
abundant species of Geometrce (Asthena candidata, 
Cabera pusaria, and C. exanthemaria) may be unpalat- 
able, for they are all white and very conspicuous when 
flying at dusk. If this be- the case it is very probable 
that the resemblance of two much scarcer Geometers to 
some of these may be an example of true Mimicry (viz. 
Acidalia subsericeata and the first mentioned ; Corycia 
temerata and the second, or both second and third). 
It is much to be hoped that the experimental evidence 
will soon be forthcoming. 

I have given many instances of Mimicry in Lepi- 
doptera because the subject has been more fully in- 
vestigated within the limits of this order, and because 
of the beauty and interest of the examples themselves. 
But the same principles are of very wide application, 
as I shall be able to show in the next chapter, although 
limited space will prevent me from giving many ex- 

1 For these and other experiments on unpalatable insects see 
Studies in the Theory of Descent, Part ii. pp. 336 40 ; English trans- 
lation by Professor Meldola. 



WE have seen that a Lepidopterous insect occasion- 
ally mimics another closely related to it, although the 
resemblance is almost invariably between distantly 
connected species; while in many cases the relation- 
ship is very far removed, as when a moth imitates the 
appearance of a butterfly. Corresponding cases occur 
in other orders of insects, but we must now pass on to 
consider some of the numerous instances in which the 
mimetic species is separated from the form which it 
deceptively resembles by the wide interval which re- 
moves one order of insects from another. 

Hymenoptera mimicked by other orders of Insects 

The Hymenoptera, including the formidable hor- 
nets, wasps, bees, and ants, are more frequently 
mimicked than any other order. In several of the 
British moths the wings have lost their scales and 
have become transparent, while the other parts have 



also been modified, so as to produce a more or less 
perfect resemblance to some stinging Hymenopterous 

Eimicry of Hymenoptera by Lepidoptera 

This is the case with two of the hawk-moths, called 
Bee Hawks (Sesia fuciformis and S. bombyliformis') , 
which in some degree suggest the appearance of 
humble-bees. The habits are, however, entirely dif- 
ferent, and the resemblance very imperfect so much 
so that a lizard (Lacerta muralis), to which I offered a 
living specimen, was not imposed upon in the least, 
but devoured the insect without hesitation or caution. 
Although humble-bees are eaten by lizards, they are 
always seized cautiously, and disabled before being 

In one respect these Bee Hawks are extremely in- 
teresting, for they provide a conclusive answer to those 
who believe that such mimetic forms have not been 
modified from a condition which is more characteristic 
of the group to which they belong. When the Bee 
Hawk emerges from the chrysalis its wings are even 
now thinly clothed with scales, which are shaken off 
in its first flight. The history of the change is still 
recapitulated, as in so many other cases, in the history 
of the individual. 

The two Hornet Clear-wing Moths (Sphecia api- 
formis and S. bembeciformis) afford far more perfect 


examples of Mimicry, the resemblance to a hornet or 
large wasp being so strong that the great majority of 
people would shrink from them in fear. The insect 
carries out the imitation to the end, and when seized 
moves its body as if it were about to sting. 

Experimental proof that Protective Mimicry at first 
deceives an enemy 

The protective effect of the resemblance was well 
seen when I offered one of these moths (S. bembeci- 
formis) to Lacerta muratis. The lizard was evidently 
highly suspicious, and yet afraid. It examined the 
insect very keenly from a distance, approached cau - 
tiously, and touched it with its tongue. The effect of 
this investigation was evidently reassuring, as we 
might expect ; for the soft scaly body of the moth is 
very different from the hard polished surface of a 
wasp or hornet. And yet the lizard seized the moth 
with the greatest care, by the head and thorax, and 
began to thoroughly crush these parts, behaving ex- 
actly as it would have done with a wasp or bee. The 
texture, and perhaps the taste, of the insect, however, 
soon revealed the deception, and the lizard then treated 
the moth as unscrupulously as any other harmless 
insect. A few days afterwards I offered another moth 
of the same kind to the same lizard ; but the lesson 
had been learnt, and the insect was seized without 


special examination or caution, and devoured directly 
it was seen. 

This experiment supports the conclusion previously 
arrived at, that insect-eating animals do not start 
with an instinctive knowledge, but learn by experience. 
It also proves that the mimetic resemblance may 
deceive a peculiarly sharp and clever enemy, and cer- 
tainly acts as a protection to the insect. In this case 
the moth was brought within a few inches of the 
lizard : in nature it would be seen from a much greater 
distance, and would, doubtless, be at once avoided, 
unless the enemy was impelled by excessive hunger. 

Mimicry of Hymenoptera by Diptera 

Other orders of insects also commonly mimic the 
Hymenoptera. A very common British insect belong- 
ing to the Diptera (the order including flies, gnats, 
daddy-longlegs, &c.) is known as the Drone-fly 
(Eristalis), although it is often wrongly called a Drone. 
It very frequently flies into houses, and may be seen 
walking, in a very bee-like manner, on the window- 
panes. In addition to the striking resemblance to a bee 
(see fig. 51) it buzzes in a most alarming manner when 
captured, and moves its body in a way that is too 
suggestive for the nerves of most people. And yet its 
anatomical structure is entirely different from that of 
a bee, and a superficial examination will show that it 


has only two wings, instead of the four possessed by 
the Hymenoptera and most of the other orders. 

FIG. 51. Drone-fly (EristaZis), to the right, and bee on a carrot-blossom ; 
natural size. 

Mimicry of Hymenoptera by Coleoptera 

Among the Coleoptera (beetles) a common English 
beetle (Clytus arietis) resembles a wasp hi a very 
striking manner (see fig. 52). The slender waist, the 
shape of the head and antennae, and the black, yellow- 


banded body are all most suggestive; and although 
the transparent wings are concealed except during 
flight, it will be remembered 
that the wings of a wasp 
attract very little attention 
under the same circumstances. 
But the most remarkable 

PIG. 52. A common British beetle . , . ., , , 

(ciytus arietis) which resembles point in the resemblance can 

a wasp ; natural size. 

only be appreciated by observ- 
ing the living insect. When walking, the slender 
wasp-like legs are moved in a rapid somewhat jerky 
manner, very different from the usual stolid Coleo- 
pterous stride, but remarkably like the active move- 
ments of a wasp, which always seem to imply the 
perfection of training. Wallace, Belt, and Semper 
also give many instances of beetles and other insects 
imitating the appearance of ants, which are extremely 
abundant, and seem to be very free from attack, in 
the tropics. 

I have chiefly selected a few common British bi- 
sects as examples of Mimicry, but the number might 
be multiplied indefinitely from the insect fauna of 
other countries. The examples are, of course, most 
remarkable when the appearance of the order to which 
the mimetic form belongs diverges most widely from 
that which includes the imitated species. 


Mimicry of Hymenoptera by Hemiptera 

The flattened bodies of the common plant-bugs 
(Hemiptera) are peculiarly characteristic, and they are 
in many ways very unlike other insects. In spite of 
the immense structural difference which separates 
them from the Hymenoptera, Mr. Belt describes and 
figures a Nicaraguan bug which mimics a hornet so 
closely that he caught it in his net, fully believing 
that it was a hornet. 

So common are mimetic resemblances in tropical 
countries, although, doubtless, unobserved by any 
except the keenest naturalists, that Mr. Belt writes : 
' Whenever I found any insect provided with special 
means of defence I looked for imitative forms, and 
was never disappointed in finding them.' Many ex- 
amples will be found in his most interesting book, 
from which I have already often quoted. 

Mimicry of Coleoptera by Orthoptera 

Many examples are also given by Wallace l and 
Semper. 2 One of the most remarkable is a grass- 
hopper (Orthoptera) from the Philippine Islands, 
which mimics a ladybird, 3 and has acquired the 
rounded convex shape which is characteristic of these 

1 Darwinism, pp. 25761. 

* Animal Life, International Scientific Series, pp. 389-91. 

Semper, loc. cit. p. 390. 


nauseous little beetles, and is so totally different from 
the usual appearance of a grasshopper. There are 
also many instances, from this and other localities, of 
insects resembling specially protected beetles. Some- 
times the peculiar defence of the mimicked species 
takes the form of a hardness so extreme that insect- 
eating animals are unable to make any way against it. 
Such uneatable beetles are generally imitated by other, 
and of ten distantly related, beetles; but there is a cricket 
(Orthoptera) which defends itself in this way. The 
active and predaceous tiger-beetles are also mimicked 
by other beetles and insects of different orders. Thus 
in the Philippines a harmless cricket mimics one of 
these dreaded insects in the closest manner. 

A wonderfully detailed example of Mimicry from 
Tropical America 

One of the most interesting cases I have yet met 
with was found by my friend Mr. W. L. Sclater in 
Tropical America. In this part of the world leaf- 
cutting ants are only too well known, being most de- 
structive of the introduced trees. They are seen in 
countless numbers passing along their well-worn roads 
to the formicarium, and every homeward-bound ant 
carries a piece of leaf, about the size of a sixpence, held 
vertically in its jaws. 1 Mr. Sclater found an insect of 
an entirely different kind, and, I believe, belonging to 

1 An interesting account of these ants, from which I have taken 
this short description, is given by Mr. Belt, Zoc. cit. pp. 71 et seq. 


a different order, 1 which mimicked the ant, together 
with its leafy burden. The piece of leaf was imitated 
by a thin, flat expansion, and the resemblance was so 
striking that Mr. Sclater's servant, who was a keen 
observer, actually believed that he was looking at an 
ant carrying its piece of leaf. 

Such cases can be explained by the operation of 
natural selection 

This last example is, as far as I am aware, unique 
in the detail with which the original is reproduced ; 
not only is the specially protected species copied, but 
it is depicted at its usual occupation, and the material 
upon which it labours is also included in the picture. 
I quote below a passage from Mr. Belt's work, be- 
cause it expresses in the clearest and simplest way 
what I believe to be a complete reply to those who 
would urge the incompetence of natural selection to 
produce so faithful and detailed a likeness. 

' The extraordinary perfection of these mimetic 
resemblances is most wonderful. I have heard this 
urged as a reason for believing that they could not 
have been produced by natural selection, because a 
much less degree of resemblance would have protected 
the mimetic species. To this it may be answered that 
natural selection not only tends to pick out and pre- 
serve the forms that have Protective Eesemblances, 

1 Professor Westwood and Mr. W. F. Kirby believe that the insect 
was one of the MembracidcB (Homoptera). 


but to increase the perceptions of the predatory 
species of insects and birds, so that there is a con- 
tinual progression towards a perfectly mimetic form. 
This progressive improvement in means of defence 
and of attack may be illustrated in this way. Suppose 
a number of not very swift hares and a number of 
slow-running dogs were placed on an island where 
there was plenty of food for the hares, but none for 
the dogs except the hares they could catch ; the slowest 
of the hares would be first killed, the swifter preserved. 
Then the slowest-running dogs would suffer, and, 
having less food than the fleeter ones, would have least 
chance of living, and the swiftest dogs would be pre- 
served ; thus the fleetness of both dogs and hares would 
be gradually but surely perfected by natural selection, 
until the greatest speed was reached that it was possible 
for them to attain. I have in this supposed example 
confined myself to the question of speed alone, but, in 
reality, other means of pursuit and of escape would 
come into play and be improved. The dogs might 
increase in cunning, or combine together to work in 
couples or in packs by the same selective process ; 
and the hares, on their part, might acquire means of 
concealment or stratagem to elude their enemies ; 
but, on both sides, the improvement would be pro- 
gressive until the highest form of excellence was 
reached. Viewed in this light, the wonderful perfec- 
tion of mimetic forms is a natural consequence of the 
selection of the individuals that, on the one side, were 


more and more mimetic, and, on the other (that of 
their enemies), more and more able to penetrate 
through the assumed disguises.' l This argument is 
of course equally applicable to the wonderful cases 
of Protective Resemblance for the sake of conceal- 

Insects mimicked by animals belonging to a 
different class 

We must now pass on to cases in which there is a 
still wider interval between the mimicker and the 
species which shelters it from attack. The Insecta 
form one important class of the sub-kingdom Arthro- 
poda, while the Arachnida (including the spiders and 
scorpions) constitute another of its classes. Very 
important anatomical differences separate these two 
classes, and yet members of the latter are known to 
mimic species belonging to the former. Thus, spiders 
which mimic ants are known in both the Old and the 
New World. One such mimetic spider was believed by 
Mr. Belt to be an ant until he had killed it. The 
antennae of the ant were represented by the two fore 
legs of the spider, and they were held and moved 
about in the characteristic manner. This resemblance 
has been explained as Aggressive rather than Protec- 
tive Mimicry, enabling the spiders to approach the 
ants upon which they are supposed to prey. Mr. Belt, 
however, points out that the ants, being free from 

1 Loc. cit. pp. 383, 384. 


attack, are very bold and fearless, so that no disguise 
is necessary in order to approach them. The spiders, 
on the other hand, are eagerly sought for by insecti- 
vorous birds; hence there is little doubt that the 
mimicry is protective. 1 

E. G. Peckham also describes two ant-like spiders 
in North America. Synageles picata (see fig. 53) is 
like an ant in form and colour ; 
but ' by far the most deceptive 
thing about it is the way in 
which it moves. It does not 
jump like the other Attidce, nor 
does it walk in a straight line, 

PIG. M. Synageles picata ; an 

anwjke spider (from Peck- but z i gzags continually from side 
to side, exactly like an ant which 
is out in search of booty. . . . The ant only moves 
in this way when it is hunting, at other times it goes 
in a straight line ; but its little imitator zigzags always.' 
Unlike Mr. Belt's spider, S. picata holds up its second 
pair of legs to represent antennae. Spiders commonly 
remain nearly motionless while they are eating ; picata, 
on the other hand, acts like an ant which is engaged in 
pulling some treasure-trove into pieces convenient for 
carrying. I have noticed a female picata which, after 
getting possession of a gnat, kept beating it with her 
front legs as she ate, pulling it about in different 
directions, and all the time twitching her ant-like 
abdomen.' This spider certainly does not molest the 

1 Loc. cit. pp. 314, 315. 


ants it resembles, so that the Mimicry is probably pro- 
tective. Synemosyna formica (see fig. 54) is even more 

Pro. 54. Synemosyna formica, an ant-like spider (from Peckham). 

like an ant than S. picata ; it also holds up its second 
pair of legs as antennae, and its walk is described as 
very different from that of closely allied spiders. 1 

Insects which mimic Vertebrate animals 

We finally reach the most remarkable cases of Pro- 
tective Mimicry, in which the defenceless form lives 
upon the reputation of some dangerous animal belong- 
ing to another sub-kingdom. 

Mr. Bates describes a South American caterpillar 
which startled him, and everyone to whom he showed 
it, by its strong resemblance to a snake, and it even 
possessed the features which are characteristic of a 
poisonous serpent. 2 

1 Loc. tit. pp. 110-12. 2 Loc. dt. p. 509. 


Equally interesting examples are to be found 
among our British caterpillars. The brown (or occa- 
sionally green) mature larva of the Large Elephant 
Hawk Moth (Chcerocampa elpenor) generally hides 
among the dead brown leaves on the older parts of 
the stem of its food-plant, the Great Willow-herb 
(Epilobium hirsutum). In this position it is difficult 
to see, for it harmonises well with the colour of its 

PIG. 55. The caterpillar of the Large Elephant Hawk Moth (Chcerocampa 
elpenor) when undisturbed ; full-fed ; natural size (from Weismann). 

surroundings. It possesses an eye like mark on each 
side of two of the body-rings (the first and second 
abdominal segments); but these markings do not 
attract special attention when the animal is undis- 
turbed. The appearance of the caterpillar is shown 
in fig. 55. 

As soon, however, as the leaves are rustled by an 
approaching enemy, the caterpillar swiftly draws its 
head and the three first body-rings into the two next 
rings, bearing the eye-like marks. These two rings 
are thus swollen, and look like the head of the animal, 
upon which four enormous, terrible-looking eyes are 


prominent. The effect is greatly heightened by the 
suddenness of the transformation, which endows an 
innocent-looking and inconspicuous animal with a 
terrifying and serpent-like appearance. I well re- 
member the start with which I drew back my hand 
as I was going to take the first specimen of this cater- 
pillar that I had ever seen. The appearance of the 
closely allied C. porcellus in the alarming attitude is 
shown in fig. 56. The posterior ' eyes ' are insignifi- 
cant in this species. 

FIG. 56. The caterpillar of the Small Elephant Hawk Moth (Chcerocampa porcellut) 
in its terrifying attitude after being disturbed (from Weismann) ; stage iv. ; 
about twice natural size. 

Such caterpillars terrify their enemies by the sug- 
gestion of a cobra-like serpent; for the head of a 
snake is not large, while its eyes are small and not 
specially conspicuous. The cobra, however, inspires 
alarm by the large eye-like ' spectacles ' upon the dilated 
hood, and thus offers an appropriate model for the 
swollen anterior end of the caterpillar with its terrify- 
ing markings. It is extremely interesting that the 
caterpillar should thus mimic a feature which is only 
deceptive in the snake itself. 


Experimental proofs of the protection afforded by 
resemblance to serpents 

The success of this method of defence depends 
upon an elaborate system of intimidation. An obvious 
criticism suggests that this interpretation is too fanci- 
ful, and that the appearance must have some other 
meaning. It is therefore of the highest importance 
to bring forward direct evidence proving that insect- 
eating animals are actually terrified by such cater- 

Professor Weismann offered a Large Elephant 
caterpillar to a tame Jay, which immediately killed 
and devoured it. His fowls were, however, much 
awed by the appearance of a larva, although after 
great deliberation one of them ventured to attack it, 
when the imposition was of course instantly revealed, 
and the caterpillar devoured. He then placed one in 
the seed-trough, and found that the sparrows and 
chaffinches were effectually kept off by it. One sparrow 
flew down obliquely, so that the caterpillar was hidden 
by the side of the trough until the bird was close upon 
it ; the instant the caterpillar was seen, the bird clearly 
showed its alarm by the sudden manner in which it 
altered its course. 1 Lady Verney also found that small 
birds would not come near a tray containing bread- 
crumbs when one of these caterpillars was placed 
upon it. 2 

1 Loc. cit. pp. 330-33. Good Wards, 1877, p. 833. 


I offered a mature larva of the same kind to a 
full-sized Green Lizard (Lacerta viridis), and closely 
watched the encounter. The lizard was evidently 
suspicious, and yet afraid to attack the caterpillar, 
which maintained the terrifying attitude in the most 
complete manner throughout. The lizard kept boldly 
advancing and then retreating in fright ; but at each 
advance it approached rather nearer to the caterpillar. 
After this had taken place many times and nothing 
had happened, the lizard grew bolder and ventured 
to gently bite what appeared to be the head of the 
caterpillar ; it then swiftly retired, but finding that 
there was no retaliation, it again advanced and gave 
a rather harder bite. After a few bites had been given 
in this cautious manner, the lizard appeared satisfied 
that the whole thing was a fraud, and devoured the 
caterpillar in the ordinary manner. There could be 
no doubt whatever that the lizard was intimidated at 
first, and that its alarm was due to the appearance of 
the caterpillar. I had often given the same lizard 
equally large hawk moth caterpillars of other species, 
and they were invariably attacked and devoured with- 
out any ceremony. I have never seen a lizard behave 
with such caution as on the occasion I have just 

Lizards have good reason for such an instinctive 
dread, for the appearance suggests that of one of their 
most terrible foes. Mr. Belt graphically describes the 
pursuit of a lizard by a snake. 'I was once standing 


near a large tree, the trunk of which rose fully fifty feet 
before it threw off a branch, when a green Anolis 
dropped past my face to the ground, followed by a 
long green snake that had been pursuing it amongst 
the foliage above, and had not hesitated to precipitate 
itself after its prey. The lizard alighted on its feet 
and hurried away ; the snake fell like a coiled-up 
watch-spring, and opened out directly to continue 
the pursuit ; but, on the spur of the moment, I struck 
at it with a switch and prevented it. I regretted 
afterwards not having allowed the chase to continue, 
and watched the issue, but I doubt not that the lizard, 
active as it was, would have been caught by the swift- 
gliding snake, as several specimens of the latter that 
I opened contained lizards.' l 

It is almost certain that these terrifying appear- 
ances in the larvae of our temperate latitudes first 
arose in warmer countries, where the danger decep- 
tively suggested by the Mimicry is real and obvious. 
The success which attends this method of defence, in 
countries where the reptilian fauna cannot be said to 
constitute a source of alarm, is similarly due to the 
inheritance of instincts which arose in the tropics, 
and which live on, as that unconquerable dread of any- 
thing snake-like, which is so commonly exhibited by 
the land vertebrates, including ourselves. 

* LOG. cit. pp. 339, 340. 


Similar mimetic resemblance in tropical larvae 

Lord Walsingham has shown me some beautiful 
specimens of an Indian caterpillar in which the terrify- 
ing ' eyes ' are placed further back than in the Elephant 
Hawks ; in fact, so far back that the appearance of a 
head cannot be produced by telescoping the front part 
into that which bears the marks. The larva, however, 
achieves the same end by doubling the front part of its 
body beneath the rest, the bend being made at the spot 
where the eye-like marks are placed, so that the 

FIG. 57. Indian larva (Ophideres) in the terrifying attitude ; full-fed ; natural size. 

latter are brought into an appropriate position at the 
anterior end, while the real head is of course concealed 
under the body (see fig. 57). The effect is not 
equal to that produced by Chcerocampa, but it must be 
very striking when the larva is partially concealed 
among the leaves of its food-plant. 
' The larva of the European Tau Emperor (Aglia 


Tau) has an eye-like mark which it can expose when 
attacked, but which is otherwise concealed. The 
appearance of the larva in its teTrifying attitude is 
shown in fig. 58. 

Fio. 58. The larva of Aglia Tau in its terrifying attitude -with the eye-Uke 
mark exposed ; full-fed ; natural size. 

It is obvious that this kind of intimidation re- 
quires a caterpillar of a considerable size in order to 
carry it off ; and as a matter of fact we never find it 
attempted by small caterpillars. A full-grown Large 
Elephant Hawk is quite as thick as a small snake, and 
when partly hidden among leaves its length might be 
safely left to the imagination. 

Some reasons why Mimicry is so frequent and perfect in 

Although mimetic resemblances are far commoner 
and more perfect among insects than any other group 
of animals, the phenomena will probably be found to 
occur very widely when attention is directed to the 
subject. It is, however, very unlikely that any one 
group of animals employs this method of defence to 
an extent which at all approaches the insects. The 
defenceless character of the group as a whole, the 


extent to which they are preyed upon by the higher 
animals, their enormous fertility, and the rapidity 
with which the generations succeed each other, are 
reasons why natural selection operates more quickly 
and more perfectly than in other animals, producing 
mimetic resemblances or other forms of Protective 
Kesemblance in number and fidelity of detail un- 
equalled throughout organic nature. 

Protective Mimicry in Vertebrata 

Mimicry is by no means unknown among the Ver- 
tebrate animals. Thus the brightly coloured snakes 
of the genus Elaps, already alluded to, are closely 
resembled by harmless snakes belonging to different 
families. The names of several mimetic species, and 
further instances of the same kind among African 
snakes, will be found in Mr. Wallace's ' Darwinism.' 
The same writer also gives many instances of Mimicry 
in birds. Thus the powerful and aggressive friar- 
birds in the Malay Archipelago are exactly mimicked 
by weak and timid orioles, representative species of 
both friar-bird and oriole occurring in several of 
the islands. 1 

Two classes of Protective Mimicry 

Two classes may be distinguished among the pre- 
ceding examples. In the vast majority of cases the 

1 Loc. tit. pp. 261-64. 


mimicking species is defended against the enemies 
which are afraid of or dislike the mimicked form. In a 
relatively few cases, however, it seems to be defended 
from the attacks of the mimicked form itself. Thus 
Bates describes a genus of South American crickets 
(Scaphura} which closely resemble 'different sand 
wasps of large size, which are constantly on the search 
for crickets to provision their nests with.' Another 
cricket resembled a predaceous tiger-beetle, and was 
' always found on trees frequented by the beetles.' 1 
A few other examples will be found in the preceding 

Aggressive Mimicry 

In most cases of Aggressive Mimicry one species 
resembles another in order to be able to approach it 
without exciting suspicion. The former is thus able 
to injure the latter in some one of the ways which 
will be described below. Aggressive Mimicry is far less 
common than Protective Mimicry. 

Trimen has shown that hunting spiders are 
sometimes very like the flies on which they prey. 
The general resemblance in size, form, and colouring 
is greatly aided by the movements of the spiders, which 
evidently mimic ' the well-known movements so cha- 
racteristic of flies.' Bates has described a Mantis which 
closely resembles the white ants on which it feeds. 

In some cases the Mimicry enables the aggressive 

1 Loc. cit. p. 509. 


form to lay eggs in the nest of that which it resembles, 
so that its larvae live upon the food stored up by the 
latter or even upon the larvae themselves. The bold- 
ness of these enemies sometimes depends upon the 
perfection of their disguise. Thus the larvae of flies 
of the genus Volucella live upon the larvae of bees and 
wasps. Volucella bombylans occurs in two varieties, 
which prey upon the humble-bees, Bombus muscorum 
and B. lapidarius, and are respectively like these Hy- 
menoptera. The resemblance is very perfect, and the 
flies enter the nests to lay their eggs. Volucella inanis 
is less like the common wasp (Vespa vulgaris), and only 
dares to lay its eggs in the evening at the entrance of 
the nest, so that the larvae may crawl in, or they or 
the eggs may be accidentally carried in by the wasps. It 
is said that the resemblance often fails to conceal the 
fly, which is then killed by the wasps. 1 Some Hyme- 
noptera also live upon the labours of other species of 
the same order, and often resemble the species they 
delude. Thus, bees of the genus Psithyrus closely 
resemble humble-bees (Bombi) : they lay their eggs 
in the nests of the latter, and their larvae are developed 
among those of the Bombi.* 

1 Mr. C. R. L. Perkins attributes the cautious habits and frequent 
failure of V. inanis to the acuteness and ferocity which distinguish 
the wasps from humble-bees. 

2 Mr. Perkins considers that the Mimicry is intended to enable the 
Psithyri to leave the nests after emerging from the pupa, rather than 
to enable the mature females to deposit their eggs in it. 


The mimicking form may prey upon some animal which 
accompanies the species mimicked 

In certain cases the Aggressive Mimicry is of a 
different kind : the mimicking species preys upon 
some animal which is not afraid of the mimicked 
species, or which even lives in company with the 
latter. Thus E. G. Peckham thinks it possible that 
the ant-like spider, Synageles picata (see fig. 53, page 
256), may prey upon beetles which accompany ants. 1 
As this does not appear to be sufficiently proved, I 
have retained the spider as an example of Protective 
Mimicry. Professor Meldola has suggested 2 that cer- 
tain ant-like spiders from Africa, described by Mansel 
Weale, are enabled to approach the flies on which they 
prey, because the latter are not afraid of ants ; for 
ants and flies may be seen feeding together upon the 
sweet secretion of the same tree. ^ 

The clear distinction of both Protective and Aggres- 
sive Mimicry into two classes I owe to E. G. Peckham. 3 

1 Loc. cit. p. 111. 

* Proc. Ent. Soc. Lond. 1878, p. xix 

Loc. cit. p. 103. 





IT has already been shown by repeated examples that, 
although the various uses of colour are quite Distinct 
from one another, they are frequently combined in a 
single animal. Thus the larvae of the Elephant Hawk 
Moths (Charocampa elptnor and C. porcettus) were 
shown to be well concealed among brown leaves ; but 
they assume a terrifying attitude when detected and 
attacked. I will now bring forward two striking ex- 
amples of the different lines of defence which are 
successively adopted by certain caterpillars. 

The larva of Puss Moth well concealed by General 
Protective Resemblance 

The larva of the Puss Moth (Centra vinuld) is 
very common upon poplar and willow. The circular 
dome-like eggs are laid, either singly or in little groups 
of two or three, upon the upper side of the leaf, and 
being of a reddish colour strongly suggest the appear- 
ance of little galls or the results of some other injury. 


The youngest larvae are black, and also rest upon the 
upper surface of the leaf, resembling the dark patches 
which are commonly seen in this position. As the 
larva grows, the apparent black patch would cover too 
large a space, #nd would lead to detection if it still 
occupied the whole surface of the body. The latter 
gains a green ground-colour which harmonises with 
the leaf, while the dark marking is chiefly confined to 
the back. As growth proceeds the relative amount of 
green increases, and the dark mark is thus prevented 
from attaining a size which would render it too con- 

PIG. 59. The larva of Puss Moth (C. vinul/i) when undisturbed; 
full-fed; natural size. 

spicuous. In the last stage of growth the green larva 
becomes very large, and usually rests on the twigs of 
its food-plant (see fig. 59). The dark colour is still 
present on the back but is softened to a purplish 
tint, which tends to be replaced by a combination of 
white and green in many of the largest larvae. Such 
a larva is well concealed by General Protective 
Eesemblance, and one may search a long time before 
finding it, although assured of its presence from the 
stripped branches of the food-plant and the faeces on 
the ground beneath. 


The same larva assumes a terrifying attitude (mimetic 
of a vertebrate appearance) when disturbed 

As soon as a large larva is discovered and disturbed 
it withdraws its head into the first body-ring, inflating 
the margin, which is of a bright red colour. There are 
two intensely black spots on this margin in the appro- 
priate position for eyes, and the whole appearance is 
that of a large flat face 
extending to the outer 
edge of the red margin 
(see fig. 60). The effect 
"is an intensely exag- 
gerated caricature of a 
vertebrate face, which is 
probably alarming to the 
vertebrate enemies of the 
caterpillar. The terrify- 
ing effect is therefore mimetic. The movements en- 
tirely depend on tactile impressions : when touched 
ever so lightly a healthy larva immediately assumes 
the terrifying attitude, and turns so as to present its 
full face towards the enemy ; if touched on the other 
side or on the back it instantly turns its face in the 
appropriate direction. 

FIG. 60. The larva of Puss Moth in its 
terrif yingattitude after being disturbed j 
full-fed ; natural size. 


Effect heightened by two pink whips 

The effect is also greatly strengthened by two pink 
whips which are swiftly protruded from the prongs 
of the fork in which the body terminates (see fig. 61). 
These prongs represent the kst pair of larval legs, 
which have been greatly modified from their ordinary 
shape and use. The end of the body is at the same 
time curved forward over the back (generally much 

FIG. 61. One of the pink whips of larva of Puss Moth, completely 
protruded from the conical receptacle ; x 4. 

farther than in fig. 60), so that the pink filaments are 
brandished above the head. Although the filaments 
are no thicker than a rather coarse cotton thread, 
they are hollow, and contain a delicate muscle which 
runs through their whole length and is attached at 
the top. When the muscle contracts the filament is 
withdrawn, being turned outside in : protrusion is 
brought about by the pressure of the blood, which 
drives the filament before it. The process could 
be almost exactly imitated by fastening a string to 
the tip of the finger of a glove and letting the string 
pass down inside the finger and out at the wri/.t. 


The finger could then be withdrawn by pulling the 
string, and protruded by blowing into the glove. The 
filaments are especially used in young and half-grown 
larvae ; the larger caterpillars often lose the power of 
protruding them. 

The appearance of the caterpillar is sufficiently 
alarming to human beings, and most people believe 
that the black marks are really eyes. Eosel was 
afraid to touch the larva when it assumed its terrify- 
ing attitude. Izaak Walton speaks of the black marks 
as ' his eyes black as jet,' in a description which, by 
the way, is a translation of the Latin account given 
by Muffett (or Moufet), 1 or more probably slightly 
modified from, the account in Topsell's 'History of 
Serpents ' (!) which is borrowed from Muffett. 8 

The care necessary if we are to obtain experimental 
proof of the protective value of such terrifying 

I have found that the marmoset was certainly 
terrified by a large Puss caterpillar, and although it 
is said to be greedily devoured by birds, I do not 
expect that the experiment was carried out in a 
manner at all fair to the larva. When a larva is un- 
scrupulously flung into a cage by some one from 

1 Insectomm sive minimorum Animalium Theatrum. London, 
1634, p. 183. 

'* London, 1658, p. 666. 


whom the birds expect to be fed, it is almost certain 
to be attacked before it has a chance of assuming its 
terrifying attitude. In conducting such an experi- 
ment a healthy vigorous larva should be chosen and 
carefully introduced, so. that it may have the same 
opportunities of defence which it would possess in 
a wild state. 

The larva of Puss Moth can further defend itself by 
ejecting ao irritant fluid 

All the defensive measures hitherto described are 
of a passive nature, but if further attacked the cater- 
pillar can defend itself in a very effective manner. 
The lower part of the red margin below the real head 
of the animal is perforated by a slit-like opening (see 
fig. 60), leading into a gland which secretes a clear 
fluid. This fluid is stored up in considerable quantity 
and is ejected with great force when the caterpillar is 
irritated. The ' face ' being turned towards any point 
at which the larva is touched, the stream is sent in 
the direction of the enemy. It has been long known 
that this fluid causes acute pain if it enters the eye. 

In working out the chemistry of this secretion I 
have been very kindly helped by many eminent 
chemists. My thanks are especially due to Professor 
R. Meldola and Mr. A. G. Vernon Harcourt. The 
secretion proved to be a mixture of formic acid and 
water : in a mature larva the proportion of acid is as 


high as forty per cent., and a twentieth of a gramme 
can be ejected if the caterpillar has not been irritated 
for some days. Half grown individuals eject nearly 
as much, but the fluid is weaker, containing about 
thirty-three to thirty-five per cent, of acid. The rate 
of secretion is slow ; two days and a half after the fluid 
had been collected from two large caterpillars they only 
yielded a fortieth of a gramme between them. 1 So far 
as we know at present, no other animal secretes a 
fluid containing anything which approaches this per- 
centage of strong acid. 

The value of this strongly irritant liquid is suffi- 
ciently obvious. I have seen a marmoset and a lizard 
affected by it, and have myself twice experienced 
sharp pain as the result of receiving a very small 
quantity in the eye. Although the secretion is there- 
fore useful as a defence against vertebrate enemies, it 
is probably chiefly directed against ichneumons. 

The most deadly enemy of the larva of the Puss Moth 

The caterpillar of the Puss Moth is especially 
attacked by an ichneumon (Paniscus cephalotes), which 
attaches its shining black eggs to the surface of the skin. 
These eggs are always fixed in such a position behind 
the head that the caterpillar cannot bite them or the 
maggots which hatch from them, and on a spot where 

1 For further details of this investigation see Report of British 
Association at Manchester, 1887, pp. 765-66. 


the ichneumon would probably escape the shower of 
formic acid. I have never witnessed the attack, but I 
imagine that the ichneumon swoops down upon the 
back of the larva just behind the head, and holds on so 
tightly with its sharp claws that it cannot be dislodged 
by the violent struggles of the caterpillar. Probably 
many fail and are struck by the acid shower, which 
has a very fatal effect upon them. 

I have enclosed ichneumons of the genus Paniscus 
in a glass cylinder containing the larvae. The latter 
showed not the slightest sign of any knowledge of 
the presence of their deadly foes, until accidentally 
touched by the ichneumons as they were harrying 
up and down in their endeavours to escape. The 
instant the larvae were touched they assumed the 
terrifying attitude and turned towards the spot, the 
lips of the opening of the gland swollen by pressure 
from within, in readiness for an immediate discharge. 
When an ichneumon was held in the forceps and thus 
made to touch the caterpillar several times, the fluid 
was ejected almost instantly, while the larva also 
made vigorous efforts to bite its enemy with its 
powerful mandibles. A little of the secretion was 
collected in a tube and placed on the ichneumons, 
which collapsed at once, and either died or took many 
hours to recover. 

When once the eggs are fixed the larva is doomed ; 
the maggots begin sucking its juices as soon as their 
heads emerge from the egg-shell, while the tail remains 


firmly adherent in the latter. They are thus tightly 
fixed to the larva by both ends. The caterpillar is 
nearly always allowed to become full grown and spin 
a cocoon before the maggots have become large. In 
this way the latter secure a safe retreat and more 
abundant food. When they have grown large and 
their prey is shrivelled and almost dead, they lose the 
attachment to the egg-shell and devour from all points, 
until nothing but a dry and empty 'skin is left. They 
then spin their own cocoons within that of the cater- 
pillar. The latter is also attacked by other parasites 
and probably often by vertebrate insect-eaters. 

A well-protected larva is often especially liable 
to attack 

Thus, in spite of the fact that the caterpillar pos- 
sesses so many defensive appliances, it is especially 
liable to attack, far more so than many other larvae 
which are less' protected. Mr. G. C. Bignell enu- 
merated seven species of parasites which attack it. At 
first sight this seems to be a difficulty, but we must re- 
member that we are probably dealing with an animal 
which has been especially attacked for a long period 
of time, and which has been saved from extermination 
by the repeated acquisition of new defensive measures. 
But any improvement in the means of defence has 
been met by the greater ingenuity or boldness of foes ; 
and so it has come about that many of the best pro- 


tected larvaB are often those which die in the largest 
numbers from the attacks of enemies. The excep- 
tional standard of defence has been only reached 
through the pressure of an exceptional need. 

The larva of Lobster Moth well concealed by Special 
Protective Resemblance 

The caterpillar which I select as a second example 
of the way in which various modes of defence may be 
combined, is that of the Lobster Moth (Stauropun 
fagi), which is rare in this country. Its usual food- 
plant is beech, and when at rest it is well concealed 
by resembling a withered leaf irregularly curled up. 
The stalk is represented by two long thin appendages, 
which, like the fork of the Puss caterpillar, have been 
modified from the last pair of claspers. At rest, these 
appendages are held together and appear to be one. 
The second and third pairs of true legs are extra- 
ordinarily long, but the length of each is halved by 
doubling in the middle, and all four doubled-up legs 
hang down in a bunch. They thus resemble in the 
most remarkable manner the bunches of brown scales 
(the stipules of the foliage leaves) which enclose the 
buds of the beech, and hang down after the latter are 
unfolded. The colour, length, and shape of each 
folded leg, and the number of legs which thus hang 
down together, are all such as strongly to suggest the 
appearance of the scales. 


The same larva assumes a terrifying attitude (mimetic 
of a spider) when disturbed 

As soon as the larva is disturbed it holds the 
anterior part erect, and assumes a terrifying position 
which mimics that of a large spider. All the points 
in a spider's attitude and appearance which impress 
the imagination are seized upon by the larva and 
exaggerated for the sake of effect, while quite novel 
touches are added with the same object. The first 
pair of legs, which are not unusually long, are held 
so as to suggest the jaws of a spider, but they are 
larger and more widely gaping than any actual jaws. 
The four elongated legs are held widely apart and 
are made to quiver in the most terrific manner, as if 
the animal was preparing to seize its prey. The hind 
part of the body is turned so far over the head that 
the two appendages project over it, and they are at 
the same time made to diverge. In this position they 
strongly suggest the appearance of a pair of antennae, 
and add an ideal finish to the apparent monster, 
which is, indeed, exactly like nothing upon earth, but 
which is, nevertheless, most effective in its appeal to 
the imagination. When the hind part is thus turned 
forward, its ventral surface of course becomes the 
dorsal surface of the abdomen of the supposed spider, 
and it is appropriately coloured and has an appearance 
of plumpness which greatly adds to the resemblance. 
When the larva is much irritated, it gently moves 


this hinder part from side to side, and with it the 
antenna-like appendages. . This movement also adds 
to the general effect. 

When the larva is slightly irritated, the position is 
often imperfectly assumed at first, but as the irritation 
is repeated and increased, the animal adds the various 
details which go to make up the terrifying attitude in 
its most perfect and elaborate form. 

Experimental proof of the protective value of the 
terrifying attitude in the Lobster caterpillar 

I offered two of these larvae to the marmoset, and 
the results proved the importance of conducting such 
experiments with the greatest care, if reliable con- 
clusions are to be obtained. The marmoset knew 
that my boxes contained insects, and was always very 
keen and excited at the sight of them. When the box 
containing one of the ' Lobsters ' was opened, the cater- 
pillar was seized and devoured before it had time to 
alter its position, and before the marmoset could have 
had the chance of being intimidated. The second 
caterpillar was placed on the table and made to assume 
its terrifying attitude, and then the marmoset was 
allowed to approach it. Although a caterpillar of the 
same size had just been eaten without the slightest 
hesitation, the marmoset was much impressed by the 
alarming sight, and only ventured to attack after the 
most careful examination, and even then in the most 


cautious manner. However, as no resistance was met 
with, the larva was soon devoured and greatly relished. 
I then tried a similar experiment with a lizard, which 
only attacked the larva after a cautious examination. 

The interpretation of the attitude assumed by 
the irritated caterpillar was originally offered by H. 
Miiller, and it may be now said to rest upon a basis 
of experimental proof. It is also very likely that the 
spider-like appearance is a defence against the insect 
enemies of S. fagi. This is rendered very probable by 
H. Miiller's observation, that ichneumons keep out of 
the way of spiders and are rarely seen in their webs. 

The Lobster caterpillar also deceptively suggests that it 
has been already stung by an insect parasite 

But the caterpillar possesses another method of 
defence, if hard pressed by an insect foe. On the side 
of each of the fourth and fifth 
body-rings there is an in- 
tensely black patch sunk below 
the general surface and con- 
cealed by a triangular flap. 
"When irritated, the flap is FIG. 62. The 4th and sth body- 

rings (1st and 2nd abdominal) 

lowered and the black patches 

seen from the right side when 

become very conspicuous (see 

fig. 62). It is probable, as H. SaSWfSfcSS. T niy 

r-n i. A j ii. L indicated in the posterior part 

Muller has Suggested, that of the 5th body-ring. 

these marks serve to imitate the appearance of 


ichneumon stings, or perhaps the result of a struggle 
with some insect enemy, in which the larva has been 
wounded. The blood of caterpillars forms a black clot, 
so that wounds are nearly always black until after 
the next change of skin. 

This is another form of mimetic resemblance the 
deceptive appearance of the traces left by an enemy 
suggesting that the larva is already ' occupied.' 

The larva of Stauropus fagi therefore bristles with 
defensive structures and methods. At rest, it is con- 
cealed by a combination of the most beautiful Protec- 
tive Eesemblances to some of the commonest objects 
which are characteristic of its food-plant. Attacked, 
it defends itself by a terrifying posture, made up 
of many distinct and highly elaborate features, all 
contributing to this one end. Further attacked, it 
reveals marks which suggest that it can be of no 
interest to an insect enemy, for another parasite is 
already in possession. 

The failure of this combination of defensive methods 

The caterpillar is so rare in this country that we 
know but little of the enemies which attack it. Two 
parasites are, however, mentioned in Mr. Bignell's list. 
Its very rarity, however, proves the constant failure of 
all defensive measures. There is little doubt that the 
larva is in the same position as that of the Puss Moth, 


but has not been equally successful. The means of 
defence have been the response on the part of the 
organism to the increasing attacks of enemies, and 
the latter on their part have met the response by 
increased vigilance, activity or boldness. Mr. Belt's 
metaphor of the mutual selective action between dogs 
and hares exactly explains the relation between these 
highly-protected larvae and their enemies, and serves 
to show why it is that less attacked larvae are also 
less defended (see pp. 253-55). 

When we compare the elaborate defence of these 
two much-persecuted larvae, with the far simpler and 
less effective protection of many caterpillars which 
are less subject to attack, we are made to realise the 
pre-eminence of natural selection in moulding the 
forms of life around us for their ceaseless mutual 




IN addition to the colours and patterns which assist 
an animal to evade or warn off its enemies or to secure 
its prey, there are also colours arid appendages which 
must have some very different meaning. These ap- 
pearances are seen in mature animals, and frequently 
undergo periodical development at times which cor- 
respond to the breeding season; and when the two 
sexes differ, the males are almost invariably the more 
brilliant. Although far less important and wide-spread 
than the protective or aggressive colours, they are 
more generally known and appreciated, because they 
are conspicuous as well as beautiful, and are freely 
displayed by the animals which possess them. 

The theory of Sexual Selection 

However these colours may have arisen, every ob- 
server must admit that they are in some way connected 
with sex. Darwin accounted for them by his celebrated 
theory of * Sexual Selection.' ' He supposed that 

1 The Descent of Man, Part ii. Sexual Selection. 


the aesthetic sense is widely distributed among the 
higher animals (vertebrates and some of the most 
specialised invertebrates), and that the colours which 
certainly appeal to this sense in man, are not without 
effect in causing gratification to the animals them- 
selves. Among the other forms of rivalry between the 
males for the possession of the females, there is rivalry 
in beauty and its appropriate display ; and the choice 
of the females being largely determined by their 
aesthetic preferences, the beauty and agility of the 
males has been gradually increased. The females 
may share in the growing adornment, for the qualities 
of the male will tend to pass over by degrees into the 
female offspring, although such tendencies will be 
often checked by the operation of natural selection, 
as Mr. Wallace has shown us in a most convincing 
manner. 1 

This explanation of the origin and meaning of 
sexual colouring is not accepted by Mr. Wallace, 
Darwin's great compeer in the discovery of the fruit- 
ful principle of natural selection, and he brings forward 
many difficulties, and suggests alternative explanations 
in his recent work on ' Darwinism.' 

It is of course quite impossible to discuss this 
most interesting and difficult subject in any adequate 
manner within the limits of the present work. This 
volume would, however, be incomplete without some 

1 Darwinism, 1st edit. chap. x. pp. 268-300. Further allusions to 
Mr. Wallace's views on the subject refer to this chapter of his work. 


account of the subject; and furthermore there are 
certain recent observations which seem to me to yield 
strong support to Darwin's theory. 

Insufficient evidence for existence of aesthetic preferences 

Mr. Wallace's chief objection is the lack of evi- 
dence that the female has any aesthetic preferences at 
all in the selection of her mate. When, however, he 
admits that display of their decorative plumage by 
male birds is ' demonstrated,' and that the females are 
in all probability ' pleased or excited by the display,' 
he certainly admits the possession of an aesthetic 
sense ; while the insufficient evidence that the final 
choice of the female is frequently determined by the 
gratification of this sense, may, I think, be chiefly due 
to want of patient or discriminating observations upon 
wild animals in their natural conditions. 

Reasons for the lack of evidence 

It is a very remarkable fact that the great impetus 
given to biological inquiry by the teachings of Darwin 
has chiefly manifested itself in the domain of Com- 
parative Anatomy, and especially in that of Embry- 
ology, rather than in questions which concern the 
living animal as a whole and its relations to the organic 
world. And yet these were the questions in which 
Darwin himself was principally interested. 


Sexual Selection is still to some extent subjudice, 
simply because the vast majority of those interested 
in nature are either anatomists, microscopists, syste- 
matists, or collectors. There are comparatively few 
true naturalists men who would devote much time 
and the closest study to watching living animals amid 
their natural surroundings, and who would value a 
fresh observation more than a beautiful dissection or 
a rare specimen. I trust that it may not be supposed 
that I in any way undervalue the immense importance 
of these other subjects ; but there are certain problems 
which they can never solve, and Sexual Selection is 
one of these. 

The only reliable evidence on this subject can be obtained 
frcm the study of wild animals in their natural sur- 

Some of the most beautiful sexual colours are 
found among the butterflies, and the males are fre- 
quently far more brightly coloured than the females. 
Mr. Wallace has pointed out that the only direct 
evidence is opposed to the theory that any choice is 
exercised by the females. The evidence depends upon 
the observations of several entomologists upon moths, 
and especially those of Dr. Alexander Wallace, of Col- 
chester, upon Bombyx cynthia. The strength of this 
evidence is much shaken by the fact that the moths 
were bred in captivity, and I think that the question 


can only be settled by careful observation under the 
most natural conditions. This conclusion is rendered 
probable by the following considerations. 

The female of the Emperor Moth (Saturnia carpini) 
is so eagerly sought by the males, that when a virgin 
female is taken into a favourable locality the collector 
is soon surrounded by troops of males which have 
been guided by a marvellously delicate sense of smell 
residing in their branching antennae. So delicate is 
the sense that the female is recognised perhaps miles 
away, and recognised as a virgin. Directly mating 
takes place the other males disappear. In this case 
selection chiefly, if not entirely, tends to improve the 
sense of smell in the males and the mode and rapidity 
of their flight. The mode of flight is probably im- 
portant in enabling the insect to cover as wide a 
volume of air as possible while it advances, and thus 
to stand a greater chance of crossing some thin 
stratum or current of air in which the odoriferous 
particles are contained. To such a selective process 
we must ascribe the wonderful antennae of these 
males and their peculiar and rapid flight. Since, 
however, both males and females are very beautiful, 
the males possessing the brighter colours, this 
example seems at first sight to support Mr. Wallace's 
views. I shall endeavour to show that the facts are 
capable of an opposite interpretation. I have here 
called attention to the habits of the species, because 
it is nearly allied to Bombyx cynthia, and because the 


keenness of the males in pursuing the females is so 
well known and remarkable, 

In spite of this very exceptional keenness in the 
wild state, my friend Dr. Dixey found in two succes- 
sive years that it is by no means easy to pair them, 
when both males and females are bred in captivity. 
I have had exactly the same experience with the con- 
tinental Tau Emperor (Aglia tau), although the 
wonderful antennae of the male show that the powers 
of this species are even more intense than those of our 
own Emperor Moth. If there is such a marvellous 
change in the disposition of these species, it is at least 
probable that similar changes occur in other species 
with more phlegmatic males. The difficulty with 
which the great majority of butterflies and moths can 
be induced to pair when bred in captivity (although 
captured females, already fertilised, will generally 
lay eggs), and the fact that an increased chance of 
success is afforded by imitating the natural conditions 
as far as possible, point in the same direction. 

The argument applies with even greater force to 
many of the higher animals. The effect of domestica- 
tion upon the brain of the domestic duck has been 
proved in the most striking manner by Sir James 
Crichton Browne. 1 The comparison between twenty 

1 The interesting facts and conclusions summarised on p. 290 were 
contained in a paper read at the meeting of the British Association 
at Sheffield in 1879. The paper has never been published, but Sir 
James Crichton Browne has kindly allowed me to use the manu- 


wild and twenty domestic ducks showed that the brain 
of the former is, in proportion to the weight of the 
body, nearly twice as heavy as that of the latter. 
The average weights were as follows : 

Domestic duck . . 1816-768 grammes 
Brain of . . 5-370 

Wild duck . . . 1155-813 
Brain of ... 6-433 
Brain weight to body weight as 1 to 338-318 in domestic duck 
1 to 179-669 in wild duck. 

These results were confirmed by the examination of 
over sixty individuals, in addition to the forty alluded 
to above. 

The effects of this degeneration are seen in the 
fact that the ' wild duck is, from first to last, a superior 
being, mentally considered, and exhibits an amount of 
intellectual and instinctive acuteness, and force and 
independence of character, to which the barn-door 
variety can make no pretension.' A careful com- 
parison of the habits and instincts of the type with 
those of the domestic race, shows that ' altogether 
there is a mental sprightliness and momentum in the 
wild duck that have no counterparts in its domestic 
congener.' The domestic duck, ever since its first 
subjugation by man, ' for eighteen centuries, and not- 
withstanding occasional infusions of wild blood, has 
been sinking into imbecility.' 

These facts are also true of many other domesti- 
cated animals, and they serve to indicate that Sexual 
Selection can only be tested fairly by the observation 


of wild forms. This is even the case with the few 
races which have, perhaps, been raised by domestica- 
tion to a higher intellectual level; for the mental 
development which has been induced by artificial 
selection has reference to the requirements or fancies 
of man, rather than to the necessities of the species. 

The ' Assembling ' of male Moths 

In many species of moths the males ' assemble ' 
round the freshly emerged female, but no special 
advantage appears to attend an early arrival. .The 
female sits apparently motionless while the little 
crowd of suitors buzz around her for several minutes. 
Suddenly, and, as far as one can see, without any sign 
from the female, one of the males pairs with her and 
all the others immediately disappear. 

In these cases the males do not fight or struggle 
in any way, and as one watches the ceremony the 
wonder arises as to how the moment is determined, 
and why the pairing did not take place before. All 
the males are evidently most eager to pair, and yet 
when pairing takes place no opposition is offered by 
the other males to the successful suitor. Proximity 
does not decide the point, for long beforehand the 
males often alight close to the female and brush 
against her with fluttering wings. 

In watching this wonderful and complicated court- 
ship, one is driven to the conclusion that the female 


must signify her intention in some way unknown to 
us, and that it is a point of honour with the males to 
abide by her decision. 

I have watched the process exactly as I have de- 
scribed it hi a common northern Noctua, the Antler 
Moth (Charaas graminis), and I have seen the same 
thing among beetles. The fact is well known to ento- 
mologists, and, as far as the evidence goes, it supports 
Darwin's theory. 

The females of certain Butterflies more beautiful than 
the males 

Another class of facts quoted by Darwin is barely 
alluded to by Wallace ; but I think that it will be of 
the utmost importance in deciding this question when 
further and more detailed observations are made. 

The females of many butterflies are more beautiful 
than the males, and then ' the plainer males closely 
resemble each other, showing that here the females 
have been modified ; whereas in those cases where the 
males are the more ornate, it is those which have 
been modified, the females remaining closely alike.' l 
Many examples are found among our British butter- 
flies, e.g. the Meadow Brown, the Clouded Yellow, 
and the Whites. The females of such species support 
the males during the marriage flight, while the oppo- 
site is known to occur in many other butterflies. It 

1 Darwin loc. cit. 1874, p. 318. 


is therefore probable that the females take the more 
active share in the wooing, and that the males have 
exercised their aesthetic preferences, and have thus 
caused their mates to be more beautiful than them- 
selves. These striking facts were brought before Mr. 
Darwin by Professor Meldola, who informs me that 
he has confirmed the facts by his own observation in 
the field. 

During the past summer (1889) I have seized every 
available opportunity of watching the wooing of our 
common- white butterflies (Pieris. brassicce, P. rap<e, 
and P. napi), and I can quite confirm Professor 
Meldola's prediction. The females were far more 
ardent than the males, and when the courtship came 
to an abrupt termination, as it generally did, it was 
invariably due to the coyness of the males. These 
facts strongly support the opinion that the beauty of 
the females has been gradually produced by the pre- 
ferences of the males. 1 

1 S. B. J. Skertchly has recently (Ann. and Mag. Nat. Hist. Sept. 
1889, pp. 209 et seq.) described a case in which the rare female of 
Ornithoptera brookeana eagerly and persistently courted a male, 
although males are more abundant and far more brilliantly coloured. 
Professor Moseley, on the other hand, describes the courtship of 
Ornithoptera poseidon in the following words : ' I once . . . was 
lucky enough to find a flock of about a dozen males, fluttering round 
and mobbing a single female. They were then hovering slowly, 
quite close to the ground, and were easily caught. The female had 
thus a large body of gaudy admirers from which to make her choice.' 
(A Naturalist on the ' Clmllenger,' 1 p. 373.) The wide difference be- 
tween these two accounts of courtship in closely allied species, proves 
the importance of making many observations before we can hope to 


Disappearance of the beauty of males when the 
females become degenerate 

I will now return to the Emperor Moth, and 
attempt to show how its bright colours can be ex- 
plained by the theory of Sexual Selection. In its 
present condition the female is certainly passive, and 
probably always accepts the attention of the first male 
to arrive. The antennae, which are so wonderfully 
complex in the males, are simple and rudimentary in 
the female, and probably valueless as sense organs. 
We must therefore believe that the conditions which 
produced the bright colours and patterns are now at 
an end, and that their disappearance is only a question 
of time. And there is evidence for both these con- 

If we examine the female chrysalis, the antennae 
are seen to be large and well- formed, and altogether 
out of proportion to the slender thread-like organs 
which are formed within them. The antennae have 
dwindled in the moth, but BO recently that the pupal 
organs within which they are formed have undergone 
but slight diminution, if any at all. This most inter- 
esting fact was brought before my notice by Professor 
Moseley. Here then we have the clearest evidence 

reach a safe conclusion. Professor Moseley's account is, however 
supported by o. large number of observations upon other species, in 
which the relation between the sexe resembles that obtaining in 


that the female Emperor was very different from the 
inert creature I have described. In the full posses- 
sion of her faculties, she doubtless took that intelligent 
interest in courtship which is to ba expected of every 
properly endowed female. 

I have also maintained that under these circum- 
stances the colours are likely to disappear. Such a 
conclusion can be tested by examining other species 
in which the degeneration of the female is more 
complete, and has doubtless occupied a far longer 

In another genus of Bombyces (Orgyia), some of 
the females (of which the common Vapourer Moth is 
an example) are far more degenerate. They never 
leave the cocoon, but lay their eggs all over it ; their 
antennae and wings are rudimentary. The male, on 
the other hand, flies actively about and has enormously 
developed antenna?. Success in courtship is almost 
certainly a mere question of speed and keen scent. 1 
In this case the male is very plainly coloured in 
various shades of brown, but he still retains a trace 
of his vanished beauty in a white spot in the centre 
of each fore wing. An examination of the pupa shows 
us that the female once possessed larger .wings and 
more perfect sense organs. 

In Psyche and allied genera the change has pro- 

1 Mr. E. B. Titchener tells me that this is not always the case; 
for a female in his possession refused the first male which arrived. 
The usual experience with the Emperor Moth, &c., seems to indicate 
that such an exception is very rare. 


ceeded much farther in the same direction. In the 
most degenerate species the female is a mere bag of 
eggs, without limbs or sense organs ; she does not 
even leave the pupa-case, but thrusts out the end of 
her body that fertilisation may take place. In the pupa- 
case of the most degenerate forms, no distinct trace of 
former organs can be made out, but in that of certain 
closely allied species they can still be recognised, 
although in a very rudimentary condition; in others 
again, still more distinctly. In the extreme forms 
the degeneration of the female has proceeded as far 
as it is possible to go, and in all it must be excessively 
ancient. The males of nearly all Psycldda are cha- 
racterised by a uniform sombre colour of a brown or 
grey tint ; all bright colours and all traces of pattern 
are almost invariably absent. 

The successive degrees of degeneration and atten- 
dant loss of colour by the males have been traced in 
species all of which belong to the Bombyces; the 
males are in all cases day-flying. The day-flying 
Bombyces, in which the females retain full possession 
of their faculties, are remarkable for the brightness 
and beauty of their colours, and this is true of species 
which are probably without any special protection by 
a disagreeable taste or smell. 

The condition presented by the Psychidce was sug- 
gested to me by my friend Mr. W. White. I could give 
many details which seem to explain the cause of the 
degeneration, but this is unnecessary for the present 


purpose. The comparison, which is, I believe, now 
made public for the first time, appears to yield a very 
strong support to the views of Mr. Darwin on this 

Sexual Selection tested by the courtship of Spiders 

Mr. Wallace quotes an opinion against Sexual 
Selection which is certainly of the greatest weight, 
that of our eminent authority on spiders, the Rev. 0. 
Pickard-Cambridge. 1 I am therefore especially pleased 
to be able to refer to an American paper which has 
appeared in the present year (1889), describing the 
most careful observations upon the courtship of 
spiders. 2 As the result of their investigations, especi- 
ally directed towards the solution of this very question 
of the existence of Sexual Selection, the authors come 
to a conclusion which is the opposite of that drawn 
by Mr. Pickard-Cambridge. 

The spiders of the family Attida, which were the 
subjects of investigation, appear to be very suitable for 
the purpose, because courtship does not appear to be 
checked or modified by confinement, as it is in so 
many Lepidoptera. The amount of labour spent in 
this admirable piece of work may be gathered from 

1 Darwinism, pp. 296-97. 

2 Occasional Papers of the Natural History Society of Wis- 
consin, vol. i. 1889, Milwaukee. Observations on Sexual Selection 
in Spiders of the Family Attida, by George W. and Elizabeth G. 


the fact that the authors ' often worked four or five 
hours a day, for a week, in getting a fair idea of the 
habits of a single species.' 

The courtship of Saitis pulex appears to be a 
most elaborate affair. A male was placed in a box 
containing a mature female. ' He saw her as she 
stood perfectly still, twelve inches away ; the glance 
seemed to excite him and he moved toward her; 
when some four inches from her he stood still, 
and then began the most remarkable performances 
that an amorous male 
could offer to an admir- 
ing female. She eyed 
him. eagerly, changing 
her position from time 
to time so that he might 
be always in view. He, 
raising his whole body 
on one side by straight- 
FIG. 63.-saitu puiex. Male dauciug ening out the legs, and 

before female (from Peckham). 

lowering it on the other 

by folding the first two pairs of legs up and under, leans 
so far over as to be in danger of losing his balance, 
which he only maintained by sidling rapidly towards 
the lowered side. The palpus, too, on this side was 
turned back to correspond to the direction of the legs 
nearest it (see fig. 63). He moved in a semicircle 
for about two inches, and then instantly reversed the 
position of the legs and circled in the opposite direc- 


tion, gradually approaching nearer and nearer to the 
female. Now she dashes towards him, while he, 
raising his first pair of legs, extends them upward 
and forward as if to hold her off, but withal slowly 
retreats. Again and again he circles from side to 
side, she gazing towards him in a softer mood, evi- 
dently admiring the grace of his antics. This is re- 
peated until we have counted 111 circles made by the 
ardent little male. Now he approaches nearer and 
nearer, and when almost within reach, whirls madly 
around and around her, she joining and whirling with 
him in a giddy maze. Again hie falls back and re- 
sumes his semicircular motions, with his body tilted 
over ; she, all excitement, lowers her head and raises 
her body so that it is almost vertical; both draw 
nearer ; she moves slowly under him, he crawling 
over her head, and the mating is accomplished. 
After they have paired once the preliminary court- 
ship is not so long.' On one occasion a female was 
the more eager of the two, but this is evidently 
very exceptional. The female always watches the 
antics of the male intently, but often refuses him 
in the end, ' even after dancing before her for a long 
time.' Such observations strongly point towards 
the existence of female preference based on aesthetic 

In Epiblemum scenicum ' the females seemed to have 
some difficulty in choosing from among the males, but 
after a decision had been reached, and a male accepted, 


there appeared to be complete agreement.' Icius sp. was 
watched for hours under natural conditions as well as 
in confinement. ' A dozen or more males and about 
half as many females were assembled together within 
the length of one of the rails. The males were 
rushing hither and thither, dancing opposite now one 
female and now another ; often two males met each 
other, when a short passage of arms followed. They 
waved their first legs, sidled back and forth, and 
then rushed together and clinched, but quickly sepa- 
rated, neither being hurt, only to run off in search of 
fairer foes.' 

The dangers of courtship were also often witnessed. 
A male of Hasarius Hoyi continued to advance after 
the female had shown signs of impatience, ' when she 
seized him and seemed to hold him by the head for a 
minute, he struggling. At last he freed himself and 
ran away. This same male after a time courted her 
successfully.' The male of Phidippus rufus was caught 
and eaten when he insisted upon showing off his fine 
points too persistently. The single female of Phidippus 
morsitans under observation ' was a savage monster. 
The two males that we provided for her had offered 
her only the merest civilities, when she leaped upon 
them and killed them.' The first pair of legs are long 
and covered with white hairs in the male : ' it was 
while one of the males was waving these handsome 
legs over his head that he was seized by his mate and 


When the males possess any special adornments 
they make a point of displaying them as fully as pos- 
sible. The male of Synageles picata (see fig. 53, page 
256) has the first pair of legs especially thickened : 
' these are flattened on the anterior surface, and are of 
a brightly iridescent steel-blue colour.' As he is ap- 
proaching the female he pauses ' every few moments 
to rock from side to side, and to bend his brilliant legs 
so that she may look full at them ; ... he could not 

PIG. 64. Habrocestum splenderu ; position of male approaching female 
(from Peckham) ; x about 8 or 9 times. 

have chosen a better position than the one he took to 
make a display.' In fact, his attitude appears to have 
first directed the attention of the authors to his pecu- 
liar beauty. The male of Dendryphantes capita tus has 
a bronze-brown face, rendered conspicuous by snow- 
white bands, and, whether intentionally or not, he 
assumes an attitude which serves admirably to expose 
this feature to the attentive female. This, however, 
is by no means his only charm, and his ' antics are 
repeated for a very long time, often for hours, when at 



. . 
of male approaching female (from Peckham). 

last the female, either won by his beauty or worn out 
by his persistence, accepts his addresses.' In the 

male of Habroces- 
tum splendens the 
abdomen is of a 
magnificent pur- 
plish red, and he 
assumes an atti- . 
tude which displays 
this beauty very 
completely (see 
fig. 64). 

The case of 
Astia vittata is es- 
pecially interesting, 
because there are 
two well marked 
varieties of male, 
one red like the 
female, and the 
other black, with 
three tufts of hair 
on the cephalo- 
thorax. The two 
forms pass into each 
other, although the 
tufts only occur in 

the fully developed niger form. The attitudes and 
movements of courtship are entirely different in the 

FIG. 66. Astia vittata, var. niger ; position of 
black variety of male approaching female (from 


two varieties (compare figs. 65 and 66) : ' the niger 
form, evidently a later development, is much the more 
lively of the two, and whenever the two varieties were 
seen to compete for a female, the black one was 
successful.' It must be admitted that these facts 
afford the strongest support to the theory of Sexual 

I have quoted much from this important paper 
because, as far as I am aware, it is the only attempt 
to solve the question by the systematic observation of 
courtship in a single group of animals. Many other 
equally interesting and significant cases are also re- 
corded, and the paper is profusely illustrated with 
representations of the most characteristic attitudes. 
As the result of the whole body of observations the 
authors are of the opinion that ' in the Attidce we have 
conclusive evidence that the females pay close attention 
to the love dances of the males, and also that they have 
not only the power, but the will, to exercise a choice 
among the suitors for their favour.' Eemembering 
that this conclusion has only been reached in the 
Attidts by the closest study, I think we may safely 
explain the smaller confidence with which we can 
speak of other animals by the want of sufficiently 
careful and systematic investigation. 


Display in courtship occurs in plainly coloured as well 
as in ornamental species 

In speaking of the display of decorative plumage, 
Mr. Wallace remarks : * It is very suggestive that simi- 
lar strange movements are performed by many birds 
which have no ornamental plumage to display.' The 
same facts are probably true of all groups of animals 
in which the males of certain species are specially 
adorned. It was certainly the case with spiders, and 
the ' assembling ' of the males of the sombre Antler 
Moth has been already described. 

The great beauty of many appearances which are, 
nevertheless, of extreme importance as Protective 
Eesemblances, is doubtless explicable in the same 
manner. It is likely that all visible parts of the 
organism, even those with a definite physiological 
meaning, appeal to the aesthetic sense of the opposite 
sex. The harsh contrasts and gaudy colours of warn- 
ing appearances, and the sombre tints which bring 
perfect concealment, must alike possess a meaning in 
courtship, but the tendency towards the develop- 
ment of higher forms of beauty is rigorously kept 
in check by natural selection. Eemove the check or 
render it less exacting, and the tendency at once 
manifests itself (see pp. 311-13). 


Such facts point towards the existence of a wide-spread 
aesthetic sense in the higher animals 

All such facts taken together seem to me to sup- 
port the opinion that an aesthetic sense exists in the 
females of all groups in which courtship is accompanied 
by display of any kind, and that the males vie in 
gratifying this sense as far as possible with whatever 
endowments they may possess. I believe that more 
extended observations like those upon spiders will 
prove that any variation of the male in the direction 
of greater adornment will, if not disadvantageous to 
the species, increase the chances of success in court- 
ship. As such new points arise the attitudes and 
movements will be modified in order to show them off 
to the greatest perfection. 

Mr. Wallace, while admitting the display and the 
pleasure given by it to the females, considers that it 
by no means follows that slight differences of shape, 
pattern, or colour would lead a female to prefer one 
male to another, ' still less that all the females of a 
species, or the great majority of them, over a wide 
area of country, and for many successive generations, 
prefer exactly the same modification of the colour or 

If, however, we consider a hypothetical case in the 
light of ascertained facts, the probabilities do not 
seem to favour Mr. Wallace's opinion. Let us sup- 


pose that the ancestor of.Synageles picata only differed 
from this species in having the first pair of legs 
coloured like the others. The whole body of facts 
brought together by G. W. and E. G. Peckham 
strongly support the opinion that any variation of the 
male with rather more brilliant first legs would be 
preferred by the great majority of females, and that 
the character and its display would be improved 
during successive generations by their continued 

The courtship of the Argus Pheasant 

Mr. Wallace says that it was the case of the 
Argus Pheasant, ' as fully discussed by Mr. Darwin, 
which first shook my belief in " sexual " or more pro- 
perly " female " selection.' ! 

Since Darwin's description and Wallace's objection, 
Mr. Forbes has given us an account of the habits of 
this bird in its native country ; and the elaborate dis- 
play of the plumage by the males and the evident atten- 
tion of the females, render it at least probable that 
the latter have decided opinions as to the relative 
beauty of their suitors, and that their preferences 
have led to the gradual evolution of the wonderful 
markings, shaded so as to represent ' balls lying loosely 
within sockets.' 2 

Mr. Forbes tells us that the bird makes ' a large 

1 Tropical Nature, pp. 205-206. 

f The Duke of Argyll in The Reign of Law, 1867, p. 203. 


circus, some ten to twelve feet in diameter, in the 
forest, which it clears of every leaf and twig and 
branch, till the ground is perfectly swept and gar- 
nished. On the margin of this circus there is invari- 
ably a projecting branch or high- arched root, at a 
few feet elevation above the ground, on which the 
female bird takes its place, while in the ring the male 
the male birds alone possess great decoration 
shows off all his magnificence for the gratification and 
pleasure of his consort, and to exalt himself in her 
eyes. When the male bird has been caught ... the 
female invariably returns to the same circus with a 
new mate, even if two or three times in succession her 
lord should be caught.' ' 

Although the head of the male is completely 
shielded by the immense fan-like expansion which he 
unfurls before the female, he can judge of the impres- 
sion he is making by pushing his head between two of 
the feathers, or by peeping round the edge of the fan. 2 

The complete subordination of Sexual to Natural 

Every one will admit that such a process as this has 
been rigorously checked by the far more important 
process of Natural Selection. But it does not there- 

1 H. O. Forbes, A Naturalist's Wanderings in the Eastern Archi- 
pelago, p. 131. 

2 Darwin, The Descent of Man, 1874, p. 398, et seq. 


fore follow, as Mr. Wallace argues, that ' the effect of 
female preference will be neutralised by Natural Selec- 
tion.' It must be remembered that such preferences 
can only decide between males which have already 
successfully run the gauntlet of by far the greatest 
dangers which beset the higher animals, the dangers of 
youth. Natural Selection has already pronounced a 
satisfactory verdict upon the vast majority of animals 
which have reached maturity. The male which has 
only just passed this test, and is nevertheless accepted 
because of some superior attraction, will soon succumb 
and will leave far less offspring than one of equal 
or perhaps inferior attractions, which is fitted to live 
for the natural term of its life. Furthermore, the 
offspring of the former will stand a greater chance of 
failure than those of the latter. Natural Selection is a 
qualifying examination which must be passed by all 
candidates for honours : Sexual Selection is an honours 
examination, in which many who have passed the pre- 
vious examination will be rejected. But the conditions 
for qualifying are more rigid than in any existing 
system ; for the candidates who have barely qualified, 
or have qualified by some piece of luck, or have failed 
to keep up to the necessary standard in after life, 
will in the end be excluded from the advantages of any 
honours they may have gained. 

Mr. Wallace states that ' the action of Natural 
Selection does not indeed disprove the existence 
of female selection of ornament as ornament, but 


it renders it entirely ineffective.' This opinion can 
hardly be maintained if we believe that such pre- 
ference leads to the failure, comparative or complete, 
of the plainer or less graceful males, although the equal 
in other respects of their more successful rivals. 
Each of these two processes will check the other: 
Natural Selection will ensure that the males which 
succeed because of their beauty are among the fittest ; 
Sexual Selection will ensure that the males which suc- 
ceed on account of their ' fitness ' are among the 
most beautiful. 

When courtship is decided by wager of battle, Sexual 
Selection is hardly called into play 

When the males habitually fight for the possession 
of the females, and successful courtship is determined 
by victory, the results are, as Mr. Wallace points out, 
due to Natural Selection rather than Sexual Selection. 
It is, I think, in favour of Mr. Darwin's theory, that any 
remarkable beauty of colour or pattern is generally 
absent when the possession of the female is determined 
by wager of battle ; while the special weapons of such 
warfare are generally wanting when any peculiar beauty 
exists : there are, however, exceptions to this rule. Mr. 
Wallace points out that ' almost all male animals fight 
together, though not specially armed,' but there is no 
evidence to show that courtship is frequently decided 
in this way. 


Battles between males are often quite unimportant 

Referring again to the spiders of the family A ttidce, 
we read, in the paper quoted on p. 297, that battles be- 
tween the males were extremely common in the breeding 
season, but nothing seemed to come of them, and they 
appeared to be supremely unimportant in determining 
the issue of courtship. Two males of Zygoballus 
bettini, 'that were displaying before one female, rushed 
savagely upon each other and fought for twenty-two 
minutes, during one round remaining clinched for 
six minutes. . . . The combatants appeared tired 
at the close of the battle, but after a short rest were 
perfectly well, and fought a number of times subse- 
quently.' Eight or ten males of the very quarrelsome 
Dendryphantes capitatus were put in a box : after two 
weeks of hard fighting we were unable to discover one 
wounded warrior.' The weaker males are probably 
often driven away, but the crucial point in courtship 
is to win the consent of the female, and this seems to 
have been obtained by the tactics already described. 

Mr. Wallace refers to the battles of butterflies, but 
such struggles are neither common enough nor fatal 
enough to be of great importance in courtship. I have 
never seen any indication of a struggle between ' assem- 
bling ' males, and the courtship of butterflies is gene- 
rally allowed to proceed unmolested in the presence 
of other males, although interference leading to a 
mild kind of struggle is by no means uncommon. 


The colours displayed in courtship are generally concealed 
at other times 

The ceaseless sway of Natural Selection over all 
the results of female choice is well seen in the arrange- 
ments by which any conspicuous adornment is con- 
cealed until it is wanted. The brilliant legs of the 
male Synageles were only observed when they were 
being specially displayed : the bright colours of the 
upper sides of the wings of most butterflies are con- 
cealed by the sombre and protective tints of the under 
sides, except during flight and the short pauses between 
the flights : the bright under wings of many moths 
are similarly concealed by the upper wings, which har- 
monise with the surroundings. 

The colours displayed in courtship are specially developed 
and specially conspicuous in species which are best 
adapted to their conditions 

An interesting contrast is afforded by species which 
are so perfectly adapted to their conditions that free 
play is given to Sexual Selection : in these, the colours 
or appendages used in courtship make up the chief 
part of the male's appearance. Mr. Wallace points to 
the abundance of birds of paradise in New Guinea, 
and of peafowls in India, as proofs that these species 
are especially well equipped in the battle of life, and 


he believes that scope has thus been given to the causes 
which have produced the sexual adornment. This 
argument of course holds good, even if we are com- 
pelled to reject the causes suggested by him. A still 
better example is afforded by the Australian pigeons, 
which ' are sometimes adorned with colours vying 
with those of the gayest parrots and chatterers.' Mr. 
Wallace explains this fact as due to ' the entire absence 
of monkeys, cats, lemurs, weasels, civets, and other 
arboreal mammals ' ; while the green colour of the 
upper part may be due to the need of concealment 
from birds of prey. In some small islands of the 
Pacific, where such foes are very scarce, the pigeons 
may assume a rich yellow colour. 1 We see the same 
tendency in those predaceous insects which have little 
to fear, and which are swift enough to catch their 
prey without attempt at concealment. 

The dangers of bright sexual colouring may be averted 
by extreme wariness 

In many cases the danger incurred by the attain- 
ment of sexual colours may be balanced by the special 
development of some quality such as extreme wariness. 
I was very much struck by the opposite kinds of 
colouring exhibited by the fish which were extremely 
abundant at low water in the rock pools at Orotava, 
Teneriffe. The colours of some were extremely beauti- 

1 Wallace, Distribution of Animals, vol. i. p. 395. 


ful and bright, but those were always very shy and 
difficult to catch ; others were protectively coloured 
and exactly resembled the sand, rock, or sea- weed, and 
these when detected were easily captured. Professor 
W. A. Herdman of Liverpool has also observed the 
same facts in other groups of marine animals. 




IT now remains to consider the causes which Mr. 
Wallace and other writers believe to have been efficient 
in producing sexual colouring. 

A wide extension of the principle of Recognition Mark- 
ings is believed largely to explain sexual colouring 

In the first place, this distinguished naturalist 
very widely extends the principle of Kecognition Mark- 
ings, and believes that one of the chief meanings of 
sexual colouring is to enable ' the sexes to recognise 
their kind, and thus avoid the evils of infertile crosses.' 
Thus he considers that ' among insects the principle 
of distinctive colouration for recognition has probably 
been at work in the production of the wonderful diver- 
sity of colour and marking we find everywhere, more 
especially among the butterflies and moths; and here 
its chief function may have been to secure the pairing 
together of individuals of the same species.' 


Recognition between the sexes appears to be complete, 
and infertile crossing does not occur even when 
two species closely resemble each other 

To this it may be replied that pairing between the 
individuals of distinct species is extremely rare, and 
does not seem to be any commoner among species in 
which this means of recognition would lead to failure. 
If the resemblance between the white variety of the 
female Clouded Yellow (Colias edasa, var. helice) and 
the female Pale Clouded Yellow (Colias hyale) does not 
lead to infertile pairing ; if the practical identity of 
the Sallow and Poplar Kittens (Cerurafurcula and C. 
bifida), of the Swallow Prominent and Lesser Swallow 
Prominent (Leiocampa dictcea and L. dlctaoides) , of 
the Common and Dark Dagger Moths (Acronycta psi 
and A. tridens), does not lead to dangers of the kind, 
we must conclude that wide differences of colour and 
pattern cannot have been produced by a gradually 
lessening number of infertile crosses. 

In the case of mimetic species, it is a comparatively 
common thing for the female of one species to be 
chased by the male of another, and yet, in spite of a 
wonderful superficial resemblance between the females, 
it is very improbable that the courtship proceeds 
beyond its most preliminary stages. The same is true 
of the Clouded Yellows referred to above, and of 
Clouded Yellows and Common Whites, These, and 
many other examples of the kind show that this means 


of sexual recognition may, and frequently does, fail 
without injury to the species. 

One of the most fundamental instincts provides 
for an unfailing recognition between the sexes, in 
which certainty is ensured by the unanimous witness 
of all the senses, so that even the closest resemblance 
between distinct species does not appear to produce 
any evils of the kind suggested by Mr. Wallace. 

The necessity for Recognition can never explain the 
aesthetic value of the results produced 

It may also be urged that the beauty of the colours 
and patterns displayed in courtship can never be 
explained by this principle. For the purposes of recog- 
nition, beauty is entirely superfluous and indeed un- 
desirable ; strongly marked and conspicuous differences 
are alone necessary. But these, which are so well 
marked in Warning Colours, are not by any means 
characteristic of those displayed in courtship. 

If an artist, entirely ignorant of natural history, 
were asked to arrange all the brightly coloured butter- 
flies and moths in England in two divisions, the one 
containing all the beautiful patterns and combinations 
of colour, the other including the staring, strongly 
contrasted colours, and crude patterns, we should find 
that the latter would contain, with hardly an exception, 
the species in which independent evidence has shown, 
or is likely to show, the existence of some unpleasant 


quality. The former division would contain the 
colours displayed in courtship and when the insect is 
on the alert, concealed at other times. 

The immense difference between the two divisions, 
the one most pleasing, the other highly repugnant to 
our sasthetic susceptibilities, seems to me to be entirely 
unexplained if we assume that the colours of both are 
intended for the purposes of recognition. But these 
great differences are to be expected if we accept Mr. 
Darwin's views ; for the colours and patterns of the 
latter division appeal to a vertebrate enemy's sense of 
what is conspicuous, while those of the former appeal 
to an insect's sense of what is beautiful. It is, of 
course, highly remarkable that our own aesthetic sense 
should so closely correspond with that of an insect. 
I believe, however, that it is possible to account for 
this wonderful unanimity in taste. 

Our standards of beauty have been largely created for us 
by insects 

Our standards of beauty are largely derived from 
the contemplation of the numerous examples around 
us, which, strange as it may seem, have been created 
by the aesthetic preferences of the insect world. One 
of the most fruitful inquiries originated by Darwin 
has been the renewed investigation of the marvellous 
relation between insects and flowers, a subject which 

had been previously attacked by Sprengel in 1798. 


Darwin's work has been extended by others, and 
especially by Hermann Miiller. As the result of these 
investigations it is now well known that the fertilisa- 
tion of flowers has been largely carried on by. insect 
agency, and that insect preferences have decided as 
to the colours and patterns which prevail among the 
wild flowers of any country. 1 This is now generally 
admitted, and as Mr. Wallace himself points out, ' we 
have abundant evidence that whenever insect agency 
becomes comparatively ineffective, the colours of the 
flowers become less bright, their size and beauty 
diminish, till they are reduced to such small, greenish, 
inconspicuous flowers as those of the rupture-wort 
(Herniaria glabra) , 2 ' 

But if this conclusion be accepted, if the beauty 
of flowers has followed so completely from insect 
selection, are we not compelled to admit that insects 
possess an aesthetic sense a sense which could dis- 
criminate between the slightly different attractions 
displayed by suitors, just as we all admit that it has 
discriminated between the slightly different attractions 
displayed by flowers ? 

1 Consult The Fertilisation of Flowers, by Hermann Miiller, 
English translation by D'Arcy W. Thompson : London. Also British 
Wild Flowers in relation to Insects, by Sir John Lubbock : Nature 

2 Z/oc. cit. p. 332. 


The musical value of the song of birds cannot be explained 
as a means of Recognition between the sexes 

Similar objections may be urged against Mr. 
Wallace's contention that the songs of birds are to 
be explained as a means of recognition, and that their 
* production, intensification, and differentiation are 
clearly within the power of natural selection.' Eecog- 
nition between the sexes, and invitation from the male 
to the female, are most important benefits conferred 
by song, but these can never account for the marvel- 
lous degree of elaboration, and the high musical value 
of the results attained by many of our singing birds. 
The beauty of song is something more than its ' clear- 
ness, loudness, and individuality,' just as the beauty 
of appearance is something more than its conspicuous- 
ness ; and the fact that these two forms of beauty are 
complementary, so that the brightest birds do not sing, 
while song birds are sober in appearance, is quite 
consistent with the origin of these qualities by the 
accumulated results of female preference. We know 
that the excessive cultivation of one taste is inconsis- 
tent with the equal cultivation of others, and when 
the small brain of a bird is constantly directed to 
appreciating the beauty of song, it may well become 
comparatively indifferent to beauty of person. Be- 
sides, the qualities conferred by this means are always 
more or less of a danger to the species, and an especi- 


ally high development in one direction will tend to 
prevent any great development in other directions. 

The habits of Bower-birds as evidence for the existence 
of an aesthetic sense 

The habits of the Australian Bower-birds are fur- 
ther evidence for the existence of a strongly marked 
aesthetic sense in birds. Just as certain females are 
gratified by the display of personal adornment on the 
part of their suitors, others are pleased by the display 
and arrangement of beautiful or curious objects col- 
lected in the bowers. The latter are built on the 
ground and are intended for courtship alone, the 
nests being formed in trees. They are often very 
elaborate structures, and each species decorates its 
bower in a different manner. The Satin Bower-bird 
collects brightly coloured feathers, bleached bones, 
and shells : ' these objects are continually rearranged, 
and carried about by the birds whilst at play.' The 
Spotted Bower-bird lines its bower with tall grasses, 
kept in place by round stones which are brought from 
great distances, together with shells. The Eegent 
bird makes use of bleached shells, blue, red, and 
black berries, fresh leaves, and pink shoots ; ' the 
whole showing a decided taste for the beautiful.' ' 

I have mentioned these well-known but most inte- 
resting facts, which were considered by Darwin as 

1 The facts are quoted by Darwin from Gould and Ramsay, 
Descent of Man, pp. 413, 414. 


'the best evidence ... of a taste for the beautiful,' 
because of the confirmation which has been afforded 
by some more recent observations upon a New Guinea 
Bower -bird. 

All the aesthetic taste of this bird appears to be 
concentrated on the bower and its surroundings, for 
the bird itself is, as its name (Amblyornis inornata) 
implies, very plainly coloured. It is called the 
Gardener Bower-bird, because of its remarkable 
habits, and its native name also means ' the gardener.' 
The bower and adjacent ' small meadow enamelled 
with flowers ' were seen by the Italian traveller, Dr. 
Beccari, 1 on Mount Arfak, in New Guinea. He states 
that the Amblyornis chooses a flat surface at the base 
of a small tree, against which, as a central pillar, it 
builds a very regular conical hut, with an opening at 
one point. The hut, which is nearly three feet in 
diameter at the base, is formed of the twigs of an 
orchid, which, being an epiphyte, bears fresh leaves 
for a very long time, and greatly adds to the beauty of 
the bower. Within the hut a small cone of moss, about 
the size of one's hand, is heaped round the base of 
the tree. 'Before the cottage there is a meadow, of 
moss. This is brought to the spot and kept free 
from grass, stones, or anything which would offend 

1 An abstract of Dr. Beccari's description appeared in The Gar- 
deners' Chronicle, March 16, 1878, with a figure of the bower re- 
produced from a painting made on the spot. This article is quoted 
in Gould's Birds of New Guinea, vol. i., which also contains a 
coloured plate founded upon the above-mentioned figure. 


the eye. On this green turf flowers and fruit of 
pretty colour are placed, so as to form an elegant 
little garden. The greater part of the decoration is 
collected round the entrance to the nest, and it would 
appear that the husband offers there his daily gifts to 
his wife.' Among the objects which were always 
brightly coloured Dr. Beccari noticed the fruit of 
Garcinia, like small apples ; the fruits of Gardenias ; 
the ' beautiful rosy flowers of a splendid new V actinium 
(Agapetes amblyornitliis) ; ' fungi, and mottled insects. 
' As soon as the objects are faded they are moved to 
the back of the hut/ It is not known whether the 
female assists the male in making the bower, which 
is believed to last several seasons. 

I think it may be safely affirmed that the expla- 
nation of sexual colours as a means of recognition can 
never account for their aesthetic value, while the ex- 
istence of an aesthetic sense, to which such characters 
may appeal, appears to be rendered certain by many 

The hypothesis that sexual colouring is due to a surplus 
of vitality or is developed in relation to underlying 

Mr. Wallace also believes that the appearance of 
beautiful colours and the growth of plumes and other 


appendages is due to a surplus of vitality, and may be 
connected with the vivacity and excitability of the 
males in the breeding season. He also accepts Mr. 
Alfred Tylor's theory that colours and patterns are 
developed in relation to underlying organs and struc- 
tures. It is convenient to discuss these two views 
together, for they have much in common. 

Mr. Tylor argued that the modification of pattern 
in the different regions of the body of such an animal 
as the zebra, is related to the changes in the various 
parts of the skeleton which are concealed beneath the 
surface ; he even believed that the black marks on the 
heads of tigers, &c., are related to the chief convolu- 
tions on the surface of the brain beneath. 

It is quite possible to understand why the pattern 
should change in the different regions of the animal 
body, because of the greater protective value or higher 
aesthetic effect of such an arrangement, so that if 
Sexual Selection be accepted Mr. Tylor's theory be- 
comes unnecessary. Furthermore, it is difficult to see 
why such an inert, although important, structure as 
the skeleton should so greatly affect the appearance of 
an animal. Why should not the liver, with its vast 
blood-supply and manifold functions, produce some 
of the effects believed to be wrought by one of the 
most passive tissues in the body ? Or if the muscles 
and nerves which follow the skeleton are supposed to 
be the efficient cause, rather than the bones them- 
selves, it must be pointed out that the structure of 


such nerve- and muscle-fibres, together with the im- 
pulses which pass along the one and the contractions 
which are evoked in the other, are essentially similar 

The colours of underlying structures may be made 
use of in many cases 

It is perfectly true that the colours of underlying 
structures may be made use of for ornamental or pro- 
tective purposes. The red colour of our blood is 
useless as colour in most parts of the body, but the 
transparency of the skin has permitted it to be made 
use of in the acquisition of 'complexion'; and I 
believe that I am not wrong in supposing that we are 
still true to the preference which has doubtless en- 
couraged the growth of this attraction. 

The same thing is true of many insects in which 
the white colour of fat, the green colour of the blood, or 
even of the food lying in the alimentary canal, may be 
employed in the production of a protective appearance 
(see p. 89, also pp. 79, 80). Natural Selection has ren- 
dered these ready-made colours available by making 
the superficial parts transparent, and in many cases 
such stint have been deepened or outlines strengthened 
by the appearance of true pigment in the skin. But 
these admitted facts do not support the theory that there 
is any necessary relationship between superficial pig- 
ment and the organs or structures which lie beneath. 


The objection to Mr. Wallace's explanation of the 
immense tufts on Birds of Paradise 

Mr. Wallace, however, follows up this idea, and 
argues that ' the immense tuft of golden plumage in 
the best known birds of paradise ' is related to the 
proximity of the most powerful muscle in the body 
(the pectoral), of certain large blood-vessels and 
nerves, and of certain parts of the skeleton. The 
contractions of the muscle mean of course a great 
expenditure of energy, but the present state of phy- 
siology lends no support to the opinion that such 
expenditure could afford any explanation of the size and 
special peculiarities of an appendage produced by an 
adjacent surface. The nervous and arterial trunks 
imply that nervous energy and food material are 
being conveyed in large quantities to the localities 
where the nerves and arteries are finally distributed ; 
but their size and importance as they pass beneath 
the base of the tuft can have no relation to the growth 
and appearance of the latter. The travelling facilities 
and means of communication in any village depend 
upon the local arrangements of its railway station and 
telegraph office ; not upon the number of express- 
trains and telegrams which rush through it on their 
way to a distant town. 


The supposed causes of colouring suggested by Wallace 
and Tylor bear no true relation to the effects 

But even greater difficulties are encountered by 
those who accept Mr. Wallace's and Mr. Tylor's views 
upon the subject. If colours and patterns were in- 
variably caused by different kinds of colouring matter 
or pigment, it might not appear to be very improbable 
that the kind of pigment, and therefore the kind of 
colour, might be slightly varied as a result of the 
causes suggested by these writers: but even then 
there would not be any foundation for the assumption 
that the pigments which produce the brightest colours 
are necessarily more difficult of elaboration than the 
others, or more likely to be formed by an organism 
with surplus vitality or upon that portion of the sur- 
face beneath which the most important functions are 
performed. A change of chemical composition will 
nearly always mean the absorption of different rays of 
light and therefore a different colour ; but the quality 
of the latter, as measured by our sesthetic sense, will 
bear no necessary relation to the strain put upon the 
organism in producing the pigment. 

When, however, we remember that a very large 
proportion of the colours and patterns distinctive of 
Bex are only partially dependent upon pigment, the 
difficulties become insuperable. Let us first consider 
the case of white, which forms an important part in 


the patterns of so many birds and mammals. The 
whiteness of a hair or feather is produced, just as the 
whiteness of snow is produced, by the presence of gas 
entangled in the loose meshes between the component 
parts of their substance (see pp. 3-6). We cannot 
suppose that the surplus vitality which is believed to 
be efficient in producing some new or especially bright 
colouring matter on one part, will on another part be 
equally efficient in withholding it ! and in causing the 
substitution of bubbles of gas. 

But white is not the only difficulty; the most 
beautiful of all colours in nature, the iridescent tints 
of many animals, are not due to pigment at all, but 
frequently to interference of light, the cause which 
produces the colours of a soap-bubble or that of 
mother-of-pearl (see pp. 6-10). 

The interference colours of animals are similarly 
due to fine lines on the surface of structures, or more 
frequently to excessively thin sheets of air or occa- 
sionally of fluid, enclosed between layers of denser 
substance. The varying tints are caused by excessively 
minute differences in the width of the chinks in which 
the air is contained. But it would be a very rash 
hypothesis which suggests that a surplus of vitality 
regulates the width of these chinks to the production 
of this or that colour. There is absolutely no reason 

1 When a permanent white patch appears upon a mammal, the 
pigment is withheld ; it is only retained, and masked by the forma- 
tion of gas-bubbles, in the whitening of existing dark hairs (sea 
pp. 98, 99). 


for believing that a width which just prevents the 
appearance of colour is an indication of want of 

We must also remember that these iridescent 
tints occur in combination with colours produced in 
other ways. If we take a hypothetical case, the 
inadequacy of ' surplus vitality ' as an explanation 
becomes at once apparent. 

Let us suppose that a male bird becomes more 
beautiful in appearance, and that the change consists 
in the addition of white feathers, of new tints or 
shades in the colours due to pigments, and of those 
due to interference. 1 We must therefore suppose that 
a ' surplus of vitality ' favours the disappearance of 
pigment and the substitution of bubbles of gas, in 
one part, although albinism affords rather strong 
evidence that such a result is certainly not an indica- 
tion of strength : we must suppose that the same 
cause favours slight changes in the chemical con- 
stitution of pigments, in other parts, involving the 
excessively unlikely hypothesis that the aesthetic 
value of the results is a measure of the difficulty 
involved in their production : and we must finally 
suppose that, elsewhere, the same cause is efficient 
in adjusting with mathematical precision the width 
of spaces in the tissue, although it is wildly im- 
probable that the minute differences which correspond 

1 Admitting, for the sake of argument, that this cause is effective 
in birds, as it certainly is in insects. 


to the production or change of colour bear such a 
relation to the vital energy expended in their develop- 
ment, that we can judge of the amount of the 
expenditure by the degree of admiration excited in 
ourselves. 1 

The effects are only explicable by a theory of 
selective breeding 

We are also required to believe that these hetero- 
geneous elements are combined by the same means 
into an elaborate and harmonious whole. A process 
of selective breeding, like that of Sexual Selection, 

1 A white peacock in the Zoological Gardens, shown to me by Mr. 
F. E. Beddard, appears at first sight to support Mr. Wallace's views ; 
for the ' pigment ' colours and ' structural ' colours are alike absent 
(see p. 11). Closer examination reveals the fact that regions in 
which ' structural ' colours usually appear are readily recognisable, 
the white being of a different quality. The ' eyes ' on the train, for 
example, are quite distinct, coming out like the pattern on a white 
damask table-cloth. 

Dr. Gadow informs me that the same fact is true of white ducks 
and drakes, the wing coverts, which are blue in normally pigmented 
individuals, exhibiting a peculiar sheen or gloss, differing from the 
rest of the plumage. Dr. Gadow states that the structural colours 
are absent, because the existence of a pigment beneath the super- 
structure is necessary in order to show them off ; and he points out 
that the ancestors of birds with such structural colours cannot well 
have been white, because the effect depends in part upon pigment. 

Mr. Gotch and I found that the ' eyes ' of the white peacock do 
not regain the normal appearance in any of the colours of the 
spectrum, nor when examined by monochromatic light. 

Inasmuch as we can trace the form and distribution of all structural 
markings in an albino animal, it is clear that the physical cause of 
the appearance is not affected by albinism, in the same manner as 
the cause of pigment colours. 


affords an explanation of the gradual growth of such 
a pattern in spite of its heterogeneous elements, an 
explanation which I do not think is supplied by any 
other theory. Mr. Wallace has greatly insisted on 
the amount of individual variation, and we know that 
variations in the minutest elements of organs must 
occur as constantly as in the organs themselves. The 
presence or absence of bubbles of gas and of pigment, 
the chemical constitution of pigments, the width of 
spaces in the tissues, are all subject to constant varia- 
tion, and afford abundant material for the production 
of any aesthetic effect, if only subjected to selective 
breeding. And I have endeavoured to show that 
selection by female preference is now supported by 
certain striking facts, which were not available when 
Darwin first argued that this principle has been effi- 
cient in producing the colours displayed in courtship. 

The unsatisfactory nature of the phrase ' surplus of vital 
energy ' 

I will only briefly allude to the unsatisfactory nature 
of such vague phrases as ' surplus of vital energy,' 
when used to explain the appearance of the definite 
results which have been described above. The only 
evidence for such surplus vitality is the excitability of 
the nervous system, which is correlated with the ac- 
tivity of the reproductive organs in the breeding sea- 
son, and which leads to violent and active movements 
generally forming part of the display in courtship. 


Certain general considerations which support Darwin's 
theory of Sexual Selection 

There are also one or two general facts which seem 
to me to strongly support the theory of Sexual Selec- 
tion, and to oppose any theory which is not based on 
selective breeding. 

Sexnal Colours only developed in species which court 
by day or twilight, or have probably done so at no 
distant date 

The appearance of beautiful colours and patterns, 
which are displayed in courtship, invariably occurs in 
diurnal or partially diurnal animals. The colours 
only appear when the conditions for female preference 
are present also. If we compare butterflies with moths, 
or moths which fly by day and twilight with those 
which fly in darkness, we find that brilliant tints and 
ornamental patterns are only found when there is light 
enough for the female to see them. The consideration 
of apparent exceptions will be found to support the 
argument. The same evidence may be drawn from 
birds and other animals. If, however, such colours 
were merely the symptom of vitality, we should not 
expect to find this invariable relationship between the 
colours of one sex and the conditions for seeing it in 
the other. 


Sexual Colours are not developed on parts of the body 
which move so rapidly that they become invisible 

Another fact of the same kind has only suggested 
itself to me lately. The bright colours of courtship 
are especially characteristic of two groups of animals, 
birds and insects, and it may not unreasonably be sup- 
posed that this fact is related to the convenient frame- 
work afforded by the surface of the wings. In each 
group we may distinguish two kinds of flight : in one 
it is produced by an excessively swift vibration of the 
wings, in the other by a relatively slow flapping move- 
ment. In the former, including the humming-birds 
and the majority of insects, the wings are quite 
invisible, owing to their rapid motion ; in the latter, 
including the majority of birds and butterflies and 
many moths, they can be easily seen. We find, as a 
general rule, that the colours distinctive of sex are 
displayed on the wings in the latter group, but are 
absent from the wings in the former. Facilities for 
female observation are thus afforded by the distribu- 
tion of colour. 

When colours are best seen from one direction, this 
corresponds with the position in which the female 
would see them 

Again, the magnificent iridescent colours on the 
wings of certain butterflies, due to interference of light, 


are best seen when the insect is looked at from in front, 
as it would be by a female when the male is approaching 
her. Mr. Wallace, however, argues that the malefollows 
the female and hovers over her, so that she can hardly 
see the upper side of his wings at all. We know but 
little of the way in which an insect sees; but the struc- 
ture of the eye as a large rounded mass made up of 
radiating elements renders it probable that any object 
which comes within the area obtained by prolonging 
the radii will be seen, provided it is at the right dis- 
tance. Hence the male would be seen approaching 
the female from behind, in front, or the side, and the 
only requisite for producing the best impression upon 
her is that his head shall be towards her, and that the 
upper side of the wings shall be seen. The courtship 
of a butterfly usually passes through three stages : in 
the first, the male sees the female and approaches 
her ; in the second, they fly together for a variable 
distance, fluttering around and about each other, 
although the male is probably the more active and 
the pursuer ; in the third, the female has been over- 
come by the attentions of the male, she no longer 
flies, but settles on the ground or a leaf, while the 
male flutters over her and finally settles also. In 
each of these phases the planes of both body and 
wings are ever shifting, and the upper side of the 
latter is certainly visible to the female from time to 
time. It is therefore most significant that the irides- 
cent colours of Diadema bolina should be seen from 


the front, while they become invisible from the side 
or from behind, for the colour is produced in such a 
way as to give the female the best chance of seeing it, 
a fact which is unexplained by any other theory of 
origin except that of Sexual Selection. At the same 
time this observation needs testing by further and 
exact observation of the habits of many iridescent 
species during courtship. 

The evidence for the gradual development of pattern 
suggests selective breeding 

The steps by which some of the most elaborate and 
wonderful appearances have arisen, are traced by Mr. 
Darwin in the most complete and convincing manner. 
When we look at the marvellous eyes upon the train of a 
Peacock, or the more beautiful markings on the feathers 
of the male Argus Pheasant, it seems impossible that so 
wonderful and complete a result can have been produced 
by the aesthetic preferences of female birds. And yet Mr. 
Darwin shows the relation between these characters and 
much simpler markings on other parts of the surface. 
He proves that the one has been derived from the other 
by gradual modification, and he points to traces of 
the original marking which persist in the complex 
appearance to which it has given rise. Such facts, 
while eminently suggestive of the progressive develop- 
ment of simple into complex markings by some 
selective agency, seem to be unexplained by any other 


theory. It is impossible to understand how any neces- 
sities for recognition, any changes in the internal 
organs, any gradually increasing vitality, could cause 
the one form of marking to develop into the other, 
along lines which correspond with the attainment of 
a gradually increasing aesthetic effect. 




IT now remains to bring together the results arrived 
at, and to show their relation to one another, in a 
system of classification. 

I have not introduced the terms proposed below 
into the earlier parts of this book : it appeared better 
first to illustrate the meaning and use of existing 
terms by the description of numerous instances. I 
trust, however, that the new terms may be found to 
be useful. My friend Mr. Arthur Sidgwick has kindly 
helped me in choosing the words. 

In the following scheme Protective and Aggressive 
Resemblances are grouped with Mimicry under the 
first head of Apatetic Colours, because an animal is 
thus made to resemble some other species or some 
other object. Protective and Aggressive Resemblances 
are classed as Cryptic Colours (Procryptic and Anti- 
cryptic), because their object is to effect conceal- 
ment ; Mimetic Resemblance and Alluring Colouration 
are called Pseudosematic Colours, because they 
usually resemble Sematic or Warning and Signalling 


Colours, and deceptively suggest something un- 
pleasant to an enemy or attractive to prey. While 
Mimetic and Alluring Colours are therefore correctly 
classed in the same group with other forms of Besem- 
blance, the terms suggested convey the relationship to 
Warning or Sematic Colours. 

The second head (Sematic Colours) includes Warn- 
ing Colours and Eecognition Markings: the former 
warn an enemy off, and are therefore called Apose- 
matic; the latter assist an individual of the same 
species, and are termed Episematic. 

The third head includes the colours displayed in 
courtship, which are therefore called Epigamic. 

The vertical arrangement in the table indicates 
the three chief divisions under which the various 
uses of colour may be grouped, together with the sub- 
division of the first into its two main classes. But 
the horizontal arrangement is also of importance ; for 
Pseudaposematic colours (I. B 1) are special and highly 
remarkable instances of Procryptic colours (I. A 1), 
and deceptively resemble Aposematic colours (II. 1). 
Similarly, Pseudepisematic colours (I. B 2) are special 
instances of Anticryptic colours (I. A 2), and may 
depend for success upon the deceptive resemblance to 
Episematic colours (II. 2).