The puss caterpillar and the effects of its sting on man

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UNITED STATES
DEPARTMENT or AGRICULTURE

DEPARTMENT CIRCULAR 288

Washington, D. C. September, 1923 |

THE PUSS CATERPILLAR AND THE
EFFECTS OF ITS STING ON MAN.

F. C. BISHOPP,

ENTOMOLOGIST, BUREAU OF ENTOMOLOGY.

CONTENTS.
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There are about 25 species representing about 8 families of lepidop-
terous larve the bodies of which are supplied with urticating hairs or
spies which produce more or less painful stings when they come in
contact with unprotected portions of the skin of man. Among these
Megalopyge opercularis S. & A. produces the severest sting of all
the forms occurring in the United States. In the South these cater-
pillars sometimes become so numerous as almost to defoliate shade
trees,but their principal claim upon our attention is their sting.

The occurrence of this caterpillar in great abundance during a
number of seasons in the last 8 or 10 years has given it considerable
notoriety in the South. It has been termed “Italian asp,” “‘ possum
bug,” “puss caterpillar,’’ and, by the Mexicans, “perrito,’’ meaning
little dog. Each of these names is assigned on account of some habit
or appearance of the caterpillar.

DISTRIBUTION.

The species has a rather wide distribution throughout the Southern
States. It has been taken as far north as Virginia, is common in
Florida, and is not infrequently met with in the central Southern
States, but appears to attain its maximum abundance in Texas,
especially from Dallas southward in the central western part of the
State. The related species Lagoa crispata Packard is very commonly
met with throughout the Northern States, but its stinging propensi-
ties are not highly developed. The family Megalopygidae is rather
large and especially developed in the Tropics, many of the species
being fairly large and several possessing urticating bristles.

53529°—23

D) Department Circular 288, U. S. Dept. of Agriculture.

HOST PLANTS.

Megalopyge opercularis has a rather wide range of host plants. It
has been reported by Watson* and others as feeding regularly on ~ ‘ |
citrus trees in Florida, and in the writer’s work in Texas has been |
taken commonly on hackberry (Celtis occidentalis), elm (Ulmus, two
or three Bice cultivated and wild plum (Prunus spp.), sycamore __
(Platanus occidentalis), and oak (Quercus, several species), and fre-

uently on rose bushes (Rosa spp.). The trees are listed in about
the order in which they are pretarred by the caterpillars as food.

DESCRIPTION OF STAGES. =

THE ADULT.

Both sexes are yellowish brown, the wings being clothed with rather long wavy hairs,
some of which are white, especially along the veins, giving an appearance of silvery
streaks. The forewings are strongly marked with dark brown, particularly toward the

Fic. 1.—Male moth of the puss caterpillar.

anterior border. The wing spread of the female is nearly 14 inches, and the male is
somewhat smaller. The legs are also covered with long hair and the tarsi, being black,
contrast rather strongly with the lighter hairs above. (See Figs. 1 and 2.)

THE EGG.

Why ese 4

The eggs are pale yellow, elongate oval, the sides nearly parallel for some distance
and the ends bluntly rounded. The average length is about 1.2 millimeters and the —
width 0.6 millimeter. The eggs are laid in rows in the form of an arc, usually 8 to12_
eggsinarow. Sometimes two or three parallel rows about one-fourth of an inch apart
are deposited, the female moving forward a little after each row is laid. As the eggs
are deposited the tip of the abdomen is swung laterally, the head of the moth serving
as a plvot. Occasionally one row of eggs is laid directly on top of another. Nearly
always the eggs are well covered with the long yellowish hairs from the abdomen of
the moth (Fig. 3), and when the insect has completed oviposition the body is often
practically denuded of hair. The head end of the embryo is toward the center of the ©
circle. The eggs are usually deposited on the leaves of trees.

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1 Watson, J. R. Insects of a citrus grove. ' University of Florida Agricultural Experiment Station Bul- —

letin 148, p. 245-246. June, 1918.

The Puss Caterpillar. 3

THE LARVA.

The first instar is about 1.5 millimeterslong. The color is usually yellowish with a
slight reddish tinge. Each of the body segments is provided with protuberances on
each side crowned with hairs, some of which are one-half to two-thirds the length of
the body, and among these hairs occur rather strong spines. These spines are only
slightly developed on the posterior segments. In the second instar the length of the
larva is about 2.3 millimeters, the color usually rather uniformly reddish yellow, the
greatest width at the anterior thoracic segment and tapering toward the posterior end.
The body is fairly well covered with tufts of rather long hairs intermixed with other
hairs somewhat wavy and often equal in length to the body. In the third instar the
larvee measure 3.1 millimeters in length. The hairs appear longer, more numerous,
and rather lighter in color than in the previous instar. In the fourth instar the larvee

Fic. 2—Female moth ofthe puss caterpillar.

measure about 3.6 millimeters in length. The hairs are more thickly set than in
earlier stages and are inclined to recurve, especially in the middle of the body, giving
a matted or bunched appearance. ‘There is apparently an increase in the number of
urticating spines with each molt.

It is believed that there are five or six instars, but owing to high mortality and over-

lapping the later stages have not been definitely separated. In the last stages the

larvee are well covered with hair, which lies rather flat, extending downward to the
surface upon which the insect rests. The larve are considerably deeper in the thoracic
region and taper toward the posterior end, the hair at that end being tufted to form a
Sort of tail. (See Fig. 4.) The hairs all arise from rather definite circlets, three rows
of which are present on each side, the dorso-lateral ones being the largest. Among the
hairs on each of these convex areas are numerous smooth yellowish spines with almost
black tips. (See Fig. 5.) The dorso-lateral rows contain from 100 to 125 each, the
lateral from 50 to 60, and the ventro-lateral rows 20 to 30 each. Close to the base of
the legs and the pseudopods is a row of small folds bearing some hair on their apexes,
pee apparently not provided with spines. The length of the mature larva is about 1
‘inc

4. Department Circular 288, U. S. Dept. of Agriculture.

The color in these later instars is extremely variable, being pale yellow, gray, red-
dish brown, or mouse color, and some few present mixtures of colors. These colors
change with the molts and do not seem to be correlated with age or food plants.

THE COCOON.

The cocoons are spun on the trunk or small branches and occasionally on the
leaves of the host trees. The first silken structure (Fig. 6) is elongate oval, and
within this is formed the more dense and tough urn-shaped cocoon with its char-
acteristic hump in the middle over the thoracic region and beautifully con-
structed beveled-edge operculum (Fig. 7). Practically all of the long hairs are shed

Fic. 3.—Eggs of the puss caterpillar on leaf, covered with hairs from body of moth.

by the larva as it spins and are interwoven with the silk, thus giving the cocoon
nearly the same range of color as shown among the caterpillars. The ventral side
of the pupa is shown in Figure 8.

LIFE HISTORY AND SEASONAL HISTORY.’

The insect spends the winter in the larva stage within the cocoon.
Pupation takes place in the early spring and the adults emerge in
April, May, and June. The moths in emerging from the cocoon
often leave the exuvie projecting from the operculum (Fig. 9).

2 In the life-history work carried out in 1914 the writer was materially assisted by W. E. Dove.

— i
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The Puss Caterpillar. 5

They are comparatively sluggish and usually mate soon after becom-
ing dry. The eggs are usually laid by the females on the leaves
nearest at hand. After oviposition there seems to be more tendency
for the moths to fly and they are occasionally seen around lights in

a city. The females usually begin deposition the day following

emergence and will lay many eggs even though not fertilized. No
indication of parthenogenesis has been noted. The number of eggs
deposited ranges from 300 to over 600. Oviposition is usually com-
pleted in 2 or 3 days, but may extend over a period of 7 or 8 days.

Fic. 4—Full-grown puss caterpillar.

The females usually die shortly after egg laying ceases and the males
live from 4 to 9 days. Oviposition proceeds freely without the moth
partaking of food, and it is believed that normally the adults do not
feed in nature.

The duration of incubation has been observed to range from 4 to
8 days. The segments of the young larve can often be seen through
the eggs several hours before hatching begins. In hatching the egg
is broken open at the tip by the larva and usually a portion of it is
eaten away, thus leaving a ragged end. The young larve feed
eregariously for several days, the leaves at first bemg minutely
skeletonized as shown in Figure 10. Later, usually in the third
instar, the larve begin to cut through the entire leaf.

Tables 1 and 2 give some of the data obtained in the study of this
insect.

6 Department Circular 288, U. S. Dept. of Agriculture.

TaBLE 1.—Megalopyge opercularis: Pupal period, oviposition, and incubation at
Dallas, Tex. :

Number of moths.

Period from . .
Date cocoons were spun or | Period ofadult | spinning or eats ia

collected. emergence. collecting to = :
emergence. | Male. ee sextet tion. ing-
1914. |
Collected: Days. |
YT Ry aaa eames Auge 3i-to Oct. 7-14 to 40-F 2) 2 13 3 12 | Sept. 1) Sept. 6
Piste See Sept.5 to Sept.6..|9tol0+......| 2] 1 0 | Sept. |
Soptrag = ee eee Sept. 21 to July 18.| 2to0302+....| 2 1 Pe eee mre
DEC Gi: oe 6 eee Ma yiSootne hess ela eas seo oe Dig ees ore May 7 None.
Spun:
Oct; 2005.35 ss eee May 5 to May 8 -..-.| 197 to 200+-..-}.....- 2 Bi = cee
29. Sool ese eeaee Apr 24 ees se cy Geen egal oe A Ree a eee
1916.
Octesi a5. eee May 30 (before) =: | 20 — = ee 2 et ee eel ies ee, ee
1920. |
duly355 = S265 eee eee SAI. Wear sae ae Soa seeneesete 1 eS eS Sea Aer ee
te iis 22 eens AUST cee eee eee Paleo octee ee 32 3| Sees
Collected |
SAL y230 5 Se Sas meee July 31 to Aug. 18-/ 1 to19+....) Il Ooh c= Aug...4 | nue. 7.
BOs heme eee July 31 to Aug. 26.| 1 to 27-++-..---| Op ES gl Gee eee doz
AS 4. Do tes eee Aug. 6 to Aug. 26. -.} 2 to 22+..-. | 11 cig eee Aug. 7

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8 Department Circular 288, U. S. Dept. of Agriculture.

The duration of the early instars has been determined rather
accurately, as shown in Table 2, but no individuals have been carried
completely through their development under close observation.
This has been due to the large percentage of mortality from disease,
especially when the larve are kept in confinement. Development
is comparatively slow, and apparently 30 to 60 days are necessary
for growth to be completed.

In Dallas the maximum number of grown larve of the first genera-
tion seem to occur in June and July, and of the second generation in
September and October. There has always been more or less over-
lapping of the two generations, however, and in some strains probably

lia. 5.—Puss caterpillar with most of hairs removed to show
clusters of spines.

there is but a single generation in a year. Pupation of the first
generation usually begins early in July and extends through the
month, and with some individuals much later. The duration of this
stage in the first or summer generation ranges from 28 to 41 days
(see Table 1). The cocoons of this generation are to be found well
scattered over the trees, frequently being attached to the leaves but
more commonly to the twigs and branches. The spinning of the
cocoons of the second generation begins in September and extends
until heavy freezes occur. With this generation there is a marked
tendency to spin up on the larger limbs and trunks of trees, and
apparently a greater number leave the trees entirely and crawl
about in search of suitable places for pupation. The tendency to
spin up in crevices and other protected places is much more marked
in this than in the summer generation. The crevices in the rough

The Puss Caterpillar. 9

bark of the hackberry trees are often seen to be filled with cocoons,
sometimes thousands of them being present on a single tree. Occa-
sionally they are seen on fences or houses, or on stones around the

bases of trees.
INJURIOUSNESS.

As has been stated, the caterpillars can be considered of com-
paratively little importance as enemies of shade trees, although on

Fie. 6—Cocoon of puss caterpillar attached to twig, side view.

certain occasions they become so numerous as to defoliate them
almost completely. This phase of the injury done by them will not
be discussed.

All stages of the caterpillar are capable of stinging. The severity
of the sting, however, increases with the size of the caterpillar.
Freshly molted skins and recently killed larve will produce mild
stings and the larve after the cocoon is spun are capable of stinging,
although the venom appears less toxic. While there is evidently a
marked difference in the susceptibility of different persons to the
effects of the sting, the general concern and excitement produced by

10 Department Circular 288, U. S. Dept. of Agriculture.

the occurrence in great numbers of the caterpillars in some of the
southern cities is sufficient evidence of the poisonous nature of the
insect. In Dallas and other Texas cities hundreds and even thou-
sands of cases of stings have occurred during a single season, and in
some cases the fear of the caterpillars became almost a mania owing
to the description of the effect of the stings which was passed from
one to another. It is possible that the effects of stings may be

Fig. 7.—Cocoon of puss caterpillar opened to show beveled cap or operculum.

made more serious by the hysteria engendered by these often exag-
gerated statements, especially if published in_ newspapers. In
San Antonio, Tex., a few years ago the caterpillars became so abund-
ant about some of the public schools, and the stings were so frequent,
that the schools in question were ordered closed until all of the shade
trees in the vicinity could be sprayed and this caterpillar brought
under control. In Dallas and Fort Worth, Tex., and other cities
the forestry departments were deluged with requests that something

The Puss Caterpillar. 11

be done to eliminate the pest, and the street trees were sprayed with
arsenicals on an extensive scale.

It has been found that the long hairs on the caterpillars are harm-
less, but the shorter spines which are hidden among them are respon-
sible for the ill effects. Most of the stings are caused by inadver-
tently pressing one of the caterpillars against an exposed part of the
body. The severity of the sting seems to depend upon the tender-
ness of the place struck and also the amount of pressure applied.
As has been stated, the severity of the reactions varies much with
the person. 3

Almost immediately after any portion of the body comes in contact
with oneof these caterpillars an intense burning pain is felt, described
bysome as similar to a severe nettlesting. Thisusually becomes worse
accompanied by itching for several minutes and persists from 1 to 12
hours and sometimes longer. Almost immediately after a sting
the area touched by the caterpil-
lar shows minute raised whitish
spots or papules which soon become
red, followed by spreading of the
inflammatory area for several inches
and often accompanied by gen-
eral swelling of the portion of the
body stung. Stings on the wrist
have been followed by a swelling
of the entire arm to almost double
its normal size. A feeling of numb-
ness which almost assumes the
characteristics of paralysis accom-
panies the swelling. This is usually
confined to the member attacked
but may be generalized. Appar-
ently stings on the neck are even
worse, as the writer has one record
of a man who was stung severely
on the neck and completely incapa-
citated, being confined to the hos-
pital. for six days. These paralytic Fia. 8.—Ventral view of pupa of puss
symptoms are often accompanied by oes
nausea and sometimes by vomiting. The stings are especially severe
among young children, who often develop considerable fever and nery-
oussymptoms. These sometimes last for a day or two and are accom-
panied by nausea, especially during the first few hours. Usually with-
in two or three hours after a sting, the reddened pimple-like swellings
at the site assume the appearance of small vesicles or blisters. These
usually persist for a few hours and then apparently harden through
absorption, leaving a roughened area. In some instances the
discoloration of the skin surrounding the point of attack is rather
marked, varying from a deep red to almost black. The paralytic
symptoms usually subside with the pain, but the local lesions often
persist for several days.

While it is certain that the spines are the direct cause of the net-
tling, it is rather difficult to explain the very severe symptoms,

12 Department Circular 288, U. S. Dept. of Agriculture.

especially those of a generalized nature. It appears that when a
caterpillar is pressed against the skin some of the spines, which are
hollow, break off and others are pulled out. Beneath the clusters of
spines apparently there are glands which secrete a poison which
passes up within the spines, much as described by Packard in the
related species Lagoa crispata Pack.* The poison glands of the
brown-tail moth have been studied by Kephart * and investigations
on the nature of the venom in that species have been carried out by
Tyzzer.®
NATURAL CONTROL.

It is fortunate that, in Texas at least, some very effective natural
control agencies are at hand. In fact it is difficult to rear larve to

Fig 9.—Cocoon of puss caterpillar with exuvie protruding after
emergence of moth.

maturity on account of the high mortality among them due to a
bacterial disease, usually manifesting itself among larve which are
half grown or larger. They become sluggish and cease to feed. After
a few days they die and become very soft, a typical result of bacterial
infection. Specimens sent to Dr. G. F. White, of the Bureau of
Entomology, were found to contain two distinct species of Micro-
coccus, but he could not state positively that they were responsible
for the mortality among the larve. In many instances this disease

8 Since this paper was prepared Dr. N.C. Foot has published some results of experiments with Megalopyge
opercularis (Jour. Exp. Med., v. 35, p. 737-753, May 1, 1922). He found that injections into rabbits and
mice of an extract of ground caterpillar skins and spines produced marked symptoms and even
death. He concludes that, ‘The poison appears to be of the nature of a venom, combined with protein
vehicles, and may beitselfa protein.”? It is rendered inert by boiling.

4 Packard, A. 8. <A study of the transformations and anatomy of Lagoa crispata Pack., a Bombycine
moth. Proc. Amer. Phil. Soc., v. 32, p. 275-292, 7pl., 1894.

5 Kephart, Cornelia F. The poison glands of the larva of the brown-tail moth, Euproctis chrysorrhoea
Linn. Jour. Parasit.,:v. 1, p. 95-103, illus., December, 1914.

6 Tyzzer, E.E. The pathology of the brown-tail moth dermatitis. Jn 2d Ann. Rpt. Supt. for Suppress-
ing the Gypsy and Brown-tail Moths, p. 154-168, Boston, 1907.

The Puss Caterpillar. LS

was directly responsible for the death of all the specimens under
observation. It seemed to spread more rapidly when they were
kept in close association, but also attacked them readily when they
were scattered on the limbs of a tree.

Since 1913, when the severe stings inflicted on man by this pest
came to the writer’s attention, there has been a very noticeable
variation in its abundance from year to year. It was very abundant
in San Antonio in 1913 and 1914, apparently decreased during the
next two years, and waves of unusual abundance have occurred
since. At Dallas the caterpillars were fairly numerous in 1914, but
less so for several years follow-
ing. There was an unprece-
dented outbreak of them dur-
ing 1920 in both Dallas and
Fort Worth, and a very marked
decrease in their number during
1921. This periodicity is no
doubt rather closely correlated
with the effectiveness of the
natural control agencies.

In addition to the bacterial
disease, and probably of even
ereater importance, are the
tachinid parasites Hxorista fla-
virostris v. d. W. (Fig. 11) and
Phorocera clarvpennis Macq.
(Fig. 12). The writer is in-
debted to Dr. J. M. Aldrich and
H. J. Reinhard for the deter-
mination of the many lots of
these flies submitted to them.
At San Antonio, Tex., in 1914,
E. flavirostris was most abund-
ant. As many as eight flies
emerged from a single cocoon,
and fully 75 per cent of thelarvee
of the fall generation were para-
sitized by the two species. At
Dallas, P. claripennis appears to
predominate. Only a single
specimen of this fly develops in
a cocoon. Hmergence usually i ;
b egins earlier in spring than Fig. pies ee Sue to the feeding
with the other species.

Both of these species have been observed to overwinter in the larva
stage in the host within the cocoon. These flies usually emerged in

March and April from cocoons spun in October and November, but

some came out in the fall. The shortest period observed from spin-
ning of the cocoon by the host to emergence of the flies was 11 days
in summer and 22 days in fall. Two specimens of LE. flavirostris
were observed to leave the caterpillar and pupate August 22, and the
adults emerged September 8.

;

14. Department Circular 288, U. S. Dept. of Agriculture.

Two specimens of the common hymenopterous parasite Chalcis
ovata Say were bred from cocoons of this moth, and specimens of the
ichneumonid (Cryptus) Compsocryptus retentor Brullé emerged in
April from cocoons collected in November.

REMEDIAL MEASURES.

The logical procedure in a case of this kind is to prevent the occur-
rence of stings by early destruction of the caterpillars, but this is
often not done. The pain from stings does
not seem to be reduced materially by appli-
cations of ammonia, soda packs, or perman-
ganate of potash, which might be expected
to counteract it. The use of tincture of
iodine on the lesions followed by cold appli-
cations apparently gives some relief. The
need is apparent of determining precisely
the toxic principle involved. ‘This is especi-
ally true since the venom seems not to be an
acid, as in the case of most insect stings.

Fic. 11.—Erxorista flavirostris, a The spraying of shade trees with lead arsen-
ee Ole oes aie ate uke pipeue of 7 pounds of powdered
arsenate of lead to 150 gallons of water, with
4 pounds of dehydrated lime added, was found very satisfactory by
Alfred MacDonald, formerly city forester in
Dallas, Tex. In afew instances in which trees
were sprayed with this mixture the writer
checked up the results and found that where
there were about 100 caterpillars on a medium-
sized tree more than half of them were found
dead on the ground four days after spraying
and a few days later every live individual had
disappeared. Weaker strengthsdid not appear
to be satisfactory because of the slowness with |
which the caterpillars were killed and thein- |‘
creased danger of having them crawl about =
and possibly produce stings. Fic. 12,—Phorocera claripennis,

K. E. Scholl of the Texas Department of — 4,perasite of the puss cater:
Agriculture states that in some spraying
against this pest done in 1914 a combination contact and poison
spray was used with good results. He used an emulsion of engine oil
and soft soap—2 gallons to 50 gallons of water—with the addition
of 2 pounds of powdered arsenate of lead.

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