Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

f

CaS tres

rn

~ * "; * J —
ae = os ~

: a
yy :

en 2%

. cn ‘
4 « - 4 “A ‘ ~~
im ‘ tr . 7

- pn

U.S. DEPARTMENT OF AGRICULTURE,
DIVISION OF- ENTOMOLOGY BULLETIN NO. 39, NEW SERIES.

L. O. HOWARD, Entomologist.

THE, CULTURE

OF

BY
-
: HENRIETTA AIKEN KELLY,
! SPECIAL AGENT-IN SILK INVESTIGATIONS.
} ty TNO Das
HE, <<
aS
i“ We
| WASHINGTON:
= GOVERNMENT PRINTING OFFICE.
: | 1903.
e's | ‘
% Sittacs Se

“DIVISION OF PNTOMOLOGY.

1, 10: Howarn, Fntomologit.
hea te a + Mery. Batornologist in: ahbege of experimental field Bank,
4 by ppl 1) (CHITTENDEN, Entomologist in charge of breeding experiments.
A, 2D. HopKiss, Entoinologisti in charge of for st inset en ised
BANE. Breyton, in charge of apicuiture. Pea
hs [UNTER, in charge of cotton-boll weevil Ee Ses Deora Peden wee 8 od:
: BY {oatiniert, ‘Tu. PERGANDE, NATHAN: BANKs, tliat, Bitamoogists,
AD Scuwarz, C7 B: Sprtpson, Investigators. ace te ron . SA 7
Miss FRA, KELLY, Npecial agent in silk investigations, BI Bn ata
as Be CLIFTON, mS oR Prart, Avevsr Brsex, Orre. ‘Hemenany, eo N oe
\ yd Us, ‘Korixsky, Assistants. aise
Se Ep ‘Hixps, G. H. Harris, H. E. Bonk, Tomponeey fil agents.
i Miss L. Seuavay, Artist. a Y's Eis eda EON GE Nis

hd
te vy Ae Xo aK

U. S. DEPARTMENT OF AGRICULTURE,

DIVISION OF ENTOMOLOGY—BULLETIN NO. 39, NEW SERIES.

L. O. HOWARD, Entomologist.

ie CUETO RE

OF

THE MULBERRY SILKWORM.

BY

HENRIETTA AIKEN KELLY,

SPECIAL AGENT IN SILK INVESTIGATIONS.

inilmcity

i
Pai
j

al

=:

fifa
amis
Iho

i

WASHINGTON:
GOVERNMENT PRINTING OFFICE.
19038.

LETTER OF TRANSMITTAL.

U.S. DEPARTMENT OF AGRICULTURE,
Division oF ENTOMOLOGY,
Washington, D. C., January 31, 1903.
Str: I have the honor to transmit the manuscript of a bulletin
which has been prepared under my direction by Miss Henrietta Aiken
Kelly, a special agent of this Division, and which treats of the culture
of the mulberry silkworm in a plain yet complete way. It is intended
to distribute it among persons who wish to begin the culture of the
mulberry silkworm in different parts of the United States. I recom-
mend that this manuscript be published as Bulletin No. 39, new series,
of this Division.
Respectfully, L. O. Howarp,
Lintomologist.
Hon. JAMES WILSON,
Secretary of Agriculture.

bo

eed i od baa Oe 3

To inaugurate the public instruction in silk culture on a modern
scientific basis this bulletin, the first of a series, is prepared.

The information given was gained at original sources, during a long
residence in Italy and France, and by practical experience under
skillful sericulturists. Many italian and French authorities have been
cited, and special acknowledgment is due to Dr. A. Hugues for per-
mission to quote from his ** Practical instructions,” recently published
in L’Intermédiare des Bombyculteurs et Entomologistes, Ardéche,

France.
HENRIETTA AIKEN KELLY.

CHARLESTON, 8. C., January 15, 1903.

=
ere

ial
| ay ie er ar
+ ae

; *
tm

oget

The food of the silkworm -.

CONTENTS.

-— eee eee ee eee ee ee ee eee ee eee eee
wee ee ee ee ee eee ew wee ee ee ee eee eee eee

Implements necessary to silkworm culture --.-......-.---.-----------------
Silkworm eggs: How to winter and hatch them ..-.-.........-..---...-------

The rearing of silkworms --
General directions... -
Ventilation ....---
Disinfection .-...--

Space required ----
Temperature ...---

The first age. ..2.-...:
The second age.....---
The third age ..-..-.---
The fourth age -....---
(he fitth spe... ... 2: .
Preparations for spinning - -

je ee ee ee eee ee ee eee ee ee eee

ee

-2- ee eee ee ee ee ee ee ee ee ee ee ee

Propane ssmemimeitr tue Market .2.-2/.1..22 22.2... s.. eo. ee eke keke

Diseases of silkworms .-.-.--
Pemtnie. <0 ~) ee, 83:

Flacherie, or flaccidity

OTe) 2 ia as, oe are

Calcino, or muscardine

ee be

a

He He

oo o> hD bk DD DD
SD HD aN

St)
nN =

ILLUSTRATIONS.

Page

Bie t= Adult silkworm 22.24. oos/4 eco eae ee aoe ee eee eee i
2,-—pille glands ina mature worm... 228253352805 03 eee ae 8
oo ne chrysalig ors Aa 5.72 0 ae tee tae ee ee pei sco 10
4:——The moth—male and. female. 322 = 2s ss see Ane ses oes 10
Light moyable shelves << 224. se Rete ed eae ee ae ee 12
G:=Che rearing Troon ': o. 2.42. kee es eee 2 ee ee eee eee 13
i-—Hot water incubator: -: tec. b5s.2 24 cs seeeee ese sen eee 15
S.—Netwused in‘ehanoime beds... 2.4428 202 osteo ee eee 20
9.—Perforated paper used inchanging beds in the second and third ages. 21
10.—Arrangement of spinning places.......-....--.-- SE eae ee ese 26
iv.— Device for removing: toss fram cocoons 2222245) 250 3 ae ee eee 27
12.—Worms affected with flacherie dying in the brush --....-...-..-...- 29
13.—Worm which died from flacherie putrefying after death .........--- 30
14.—Worm emaciated from gattine after the fourth molt -....-...--.---- 30
#5. --Calcinated WOrMm. 5.32024 225.0322 a ee ete ts =e oe eee ee 31

6

THE CULTURE OF THE MULBERRY SILKWORM

The caterpillars of many moths and of a few butterflies produce silk,
but certain of those belonging to the family Bombycidae, or true silk-
spinners, particularly Bombyx (Sericaria) mori, or the mulberry silk-
worm, yield the most and the best silk. The races of Bombyx mori
to-day are the result of domestication and artificial rearing, and the
wild type is uncertain, though most authorities assign the foot of the
Himalaya as the cradle of the mulberry silkworm. It has been indus-
trially cultivated in China from time immemorial, and in Europe since
the sixth century.

THE LIFE OF THE SILKWORM.

Like all insects of its class, before arriving at the perfect winged
state, it exists (1) as a caterpillar or larva, and (2) in a chrysalid state.

Ce ose Pee ae eee Meme ae. ae} 2

Fig. 1.—Adult silkworm: 1, head; 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, rings; 11, horn; 13, 3 pairs of articulated
legs; 14, 4 pairs of abdominal or false legs; 15, a pair of false legs on the last ring.

THE LARVA, OR CATERPILLAR.

The larva (fig. 1) has a cylindrical body composed of 12 rings; each
of the first three rings has a pair of jointed legs, and the sixth, seventh,
eighth, ninth, and twelfth each bears a pair of false legs, destined
later to disappear. 3

The black elliptical spots on the side are the orifices for breathing,

and are called stigmata or spiracles.

~

8 THE CULTURE OF THE MULBERRY SILKWORM.

The head is a small mass covered with a hard scale, and is provided
with jaws that move laterally, like the wings of a folding door. The
alimentary canal extends throughout the entire length of the body,
and on each side of it is placed a silk gland (fig. 2). These consist of
two whitish or amber-colored cords, which after innumerable curves
unite in the spinneret in the region of the mouth. There are also two
glands, whose excretory canal opens in the spinneret, and covers the
silk as it comes out with an impermeable varnish rendering it insoluble

in acids and alkalies. This varnish is about a

f fifth of the weight of the thread.
Wx2--Y Hatchings usually occur annually in the

spring. Simple contact with the air causes the

new-born insect immediately to acquire a vol-

c ume larger than it had in the egg, and it quickly

begins to gnaw the under surface and edges of

the mulberry leaf. It eats day and night at

ei all hours, except when asleep, and in about

| thirty days grows 14,000 times larger than it
was at birth.

As the silkworm grows larger it becomes

paler in color, because its dark chestnut brown

hairs are scattered over a larger surface, thus

: showing more of the true color of the skin.

sed 2 a About five days from its birth the vitality
f

Ve of the larva decreases, and it eats scantily or
E not at all,and becomes thin and whitish in color.
: Then it moves around unquietly, and finding a
convenient place attaches itself to it, holding on

by its false feet. It thus remains motionless,
rae aaa eee with the front part of its body raised up, for a
glands which secrete the period of time varying according to tempera-
pee Asana ther ture, and takes its first so-called ‘‘sleep,” or
neret; g, accessory glands molt, during which time the body undergoes
ea. trom Verson and extraordinary modifications. The skin is en-
tirely shed, and all the tissues that can not keep

up with the rapid growth of the insect are changed.

The scale which covers the snout is the first part of the case to fall,
and a new case appears under the former one. The worm then pushes
itself forward through its first ring, sets at liberty the legs of the
thorax, and by a wriggling movement comes out of its old sheath.

To aid the insect in this difficult change a liquid is secreted between
the old skin and the one forming beneath it, which facilitates the
separation.

The life of the larva is usually divided into five ages, varying in

<Q)

:
|

“LIFE OF THE SILKWORM. gy

length according to temperature, frequency of feeding, race, and the
robustness of the worm. The following is about the average:

First age, from birth to first molt, five to six days.

Second age, from first to second molt, four days.

Third age, from second to third molt, four to five days.

Fourth age, from third to fourth molt, five to seven days.

Fifth age, from fourth molt to maturity, seven to twelve days.

Some time after each molt, perhaps the time needed to regain lost
strength and to solidify the newly-formed organs, the worm remains
in a state of relative torpor. Not much practice is needed to recognize
when it has come out of its ‘‘sleep.” It moves its head and thorax,
which are whitish, while the rest of the body is gray, and has com-
pletely lost the shining aspect which it had when the worm began to
molt. When fairly through its first molt the larva begins again to eat,
and its hunger does not cease until it is ready for a new molt.

Four molts having been made, the worm eats a prodigious quantity of
leaf until it reaches its maximum growth, when its appetite diminishes
and ceases altogether. It then stops moving and remains for some
time in repose, evacuating, meanwhile, its digestive canal, thus losing
up to 12 per cent of its weight. Its lean body is now white or yellow,
according to the race, and semitransparent.

Very soon it begins to move about again, lifts up its head, which is
longer and more pointed, and turns in every direction seeking to find
a convenient angle, finding which, it throws out a silk thread from its
spinneret. First a net is formed to hold the cocoon which is to be
spun, then the regular spinning begins and the form of the cocoon is
designed. For some time through the veil which very soon is to sur-
round it, the diligent larva, with its back turned outward, may be seen
completing its task. It is calculated that with its head alone the silk-
worm makes 69 movements every minute, describing ares of circles,
crossed in the form of the figure 8 (fig. 3, @).

Meanwhile the web grows closer and the veil thickens, and in about
seventy-two hours the worm is completely shut up in its cocoon, which
serves it as a protective covering.

THE CHRYSALIS.

In the cocoon the silkworm goes through the last phase of its larval
life. After four or five days the skin breaks, and the insect which
issues from this old covering is the chrysalis, whose weight is often
only half that of the larva at its highest development (fig. 3).

The chrysalis seems to have neither head nor feet, is golden-colored at
first, and then turns chestnut brown. ‘The skin dries rapidly and forms
a hard case, on which the lines of only the posterior rings are seen, the
place of the first three rings being covered with the wing-cases.

10 THE CULTURE OF THE MULBERRY SILKWORM.

The chrysalid state is in certain respects a sleep and in others a period
of great activity, in which the entire being is transformed. Wings,
antenne, reproductive organs, and legs are all now developed. This

Fic. 3.—The chrysalis: a, silkworm completing its cocoon; b, cocoon and echrysalis—ecast-off skin of
larva beneath; c, back view of chrysalis; d, side view of chrysalis. (Redrawn from Maillot.)

state lasts from eighteen to twenty days, according to the temperature.
Then the metamorphosis is complete, and the sheath breaks in the
region of the head and out of the old case the moth or perfect insect
issues.

THE MOTH.

The larva in spinning the cocoon leaves one end less dense, so that
the threads open freely to permit the egress of the moth. By the aid
of an alkaline fluid the moth sof-
tens and parts the threads and lib-
erates itself.

The moth (fig. 4) comes out of
the cocoon, as the larva out of the
ege, in the early morning hours.
It bas a distinct head, thorax,
and abdomen, four wings, two
comb-shaped antenne, three pairs
of legs, and a pair of compound
eyes.

Shortly after emerging, the
moth deposits a liquid substance,
generally white, sometimes color-
less and sometimes reddish, and
then the union occurs, lasting sev-
eral hours, after which the eggs
are laid either immediately or in
the course of four or five hours.

A gelatinous substance supplied by two glands near the extremity
of the oviduct covers the eggs as they come out, and causes them to
adhere to the substance on which they are laid.

\

it SE

‘
Wega

Fie. 4.—The moth: a, the male; b, the female

ae elas ot: ok a Ee Cee

FOOD OF THE SILKWORM. 11

The laying, consisting of 300 to 700 eggs, is generally completed in
three days, 70 to 80 per cent being deposited the first day, 20 to 30 per
cent the second day, and a few the third day. The mother moth
dies six to twelve days later, her death being usually preceded by that
of the male. Death occurs more or less speedily, according to the
robustness of the moth, the temperature, and the tranquillity in which
it has been left.

Thus in about sixty-five days the silkworm has completed its cycie
of existence, its three periods being thirty to forty days in a larval
state, fifteen to twenty days as a chrysalis, and eight to twenty days
as a moth or perfect insect.

The rapid development of the silkworm and its marvelous transfor-
mations indicate extraordinary power and very active functions. Its
respiration is almost equal to that of the frog and of certain large
birds, which is equivalent to saying that it must be always surrounded
by plenty of pure air.

THE FOOD OF THE SILKWORM.

The leaf of the white mulberry“ is the natural and the best food for
the silkworm. There are many varieties of the white mulberry—some
much better adapted than others to commercial silk culture, and some
better suited to certain localities.

The race, the size of the worms, the variety and age of the mulberry, .
the nutritive quality of the leaf, the year, the season, and the climate
make the requisite quantity of leaf very variable. The following is
given as a basis of calculation, all circumstances being considered, and
the leaves not being cleaned: For the larve hatched from 1 ounce of
eggs, during the first age, 11 pounds of leaves; during the second age,
26 to 33 pounds; during the third age, 88 to 145 pounds; during the
fourth age, 264 to 352 pounds; during the fifth age, 1,540 to 1,760
pounds; or about 2,200 pounds in all, of which one-half is consumed
in the last’six or seyen days of the fifth age.

The age of the leaf should be relative to that of the worm. Young
worms fed on old leaf, or old worms fed on young leaf, are apt to
become diseased, and even though they may not die, will scarcely
mount or will spin indifferently. A change of leaf, too, should, if pos-
sible, be avoided, or made gradually. Fresh leaf only should be used,
and never when wet with dew or heated, or before it has in a measure
acquired the temperature of the room in which the worms are being
reared. It should be gathered early in the morning or in the evening
and should not be bruised or torn, nor should the baskets or aprons used
to carry it be the same which are used to remove litter. To avoid
fermentation the leaves must be spread out ina cellar or cool, dark-

“For complete information regarding the mulberry, see Bulletin No. 34, Bureau of
Plant Industry, U. 8. Department of Agriculture.

12 THE CULTURE OF THE MULBERRY SILKWORM.

ened room. Cut up only a limited quantity of leaf at a time and
cover with a damp cloth to keep fresh, but never submerge the leaf in
water, as this is apt to occasion flacherie, a very destructive disease.
From the fourth age on there should always be a day’s supply ahead,
so that in case of rain the worms will not have to fast.

In gathering leaf, always strip the branches from base to top, so as

not to tear the bark and in-
] jure the new buds. It is
above all essential to strip
the tree entirely of its leaves,
for if leaves are left on some
branches they will there at-
tract the sap, while the bare
branches will be imperfectly
nourished. Alwaysstrip the
young trees first. The sacks
for holding the leaves should
have a hoop around the open-
ing and a hook to suspend
them to the branches.
Restricting the height of
. the trunk of the mulberry to

5 or 6 feet makes it possible
for old women and children
to gather leaf, thus diminish-
ing the cost of labor one-
half, a most important point
in commercial silk culture.

It is also important to cul-
tivate trees that bear little
or no fruit, for the production of fruit not only consumes part of the
strength of the tree, but much labor is involved in being compelled
to divest the branches of fruit before they can be used as food for
silkworms.

The stump mulberry, or that growing low like a shrub, the hedge
mulberry, and that which grows along walls vegetate much earlier than
the medium and high trunk trees. Silkworm rearers should always
have a ready supply of leaf for the first ages of the worm, and
especially is this necessary if early cultures are desired with a view to
escaping the heated days of May and June.

4,
x)

mT Y

4
SN)
Y
()
é)
0
‘

Si
Y)
‘
Ox
y
mY
4,

)
Nas

Fie. 5.—Light movable shelves.

;—~*

= ©.

IMPLEMENTS USED IN SILK CULTURE. 13

IMPLEMENTS NECESSARY TO SILKWORM CULTURE.

Commercial silk culture requires a smaller outlay of capital than
almost any other industry. The net gain the first year may pay for
an outfit which will last for many years. The following articles are
indispensable:

(1) Some very light movable shelves, permeable to air, for the first ages; and, for
the following ages, latticed shelves about 33 feet wide, and stands to support them.

(2) Unsized ordinary wrapping paper or newspapers to cover the shelves.

(3) A small ladder, if necessary, to reach high shelves.

(4) Small trays to remove worms.

(5) Knives to cut leaves and baskets to distribute them. .

(6) Coarse tulle and nets or perforated paper for changing beds and equalizing the
worms.

(7) A supply of brush, straw, or shavings to construct the spinning place.

(8) A thermometer.

Fie. 6.—The rearing room (after Gobin).

Wire, twine, laths, or canes are suitable for the lattice work of the
shelves. Make the space between the shelves about 14 inches. If
possible, do not arrange the shelves along the wall, and allow a good
passage between the tiers of shelves (figs. 5 and 6).

SILKWORM EGGS: HOW TO WINTER AND HATCH THEM.

There are two kinds of silkworm culture: One for production and
one for reproduction. The object in the first case is to get the
greatest yield of cocoons, and with a little training, may be carried
on by anyone of ordinary intelligence.

14 THE CULTURE OF THE MULBERRY SILKWORM.

The aim in culture for reproduction is to secure eggs free from
hereditary tamt of disease, and experts only can be depended on
to conduct it. Besides a careful physiological examination through-
out the rearing, the body of the mother moth is microscopically
tested after death, and her eggs are not retained if signs of disease
are discovered. In this way the birth of healthy worms is insured.
Pasteur first applied this method of selecting silkworm eggs, and thus
checked the plague (pebrine) which was rapidly destroying silkworm
culture in Europe.

Formerly, through an indiscriminate use of eges, disease invaded
the rearings to such a degree that from 65 to 90 pounds of cocoons
was considered a good yield per ounce of eggs. At the present low
price of silk such cultures are no longer remunerative, and industrial
silk culture now demands the exclusive use of scientifically tested eggs.

The grainage, or preparation of eggs for market, constitutes a special
department of silk culture. In Italy there are over -400 establish-
ments which supply eggs to raise the annual silk crop. The poorest
peasant, though well skilled in the art of rearing silkworms, would
not risk a rearing with eggs which have not been selected and pre-
served by experts.

The eggs of crossed races are best for cultures with a view to pro-
duction of silk, and here, as much as in the examinations which have
been referred to, the knowlege of experts 1s needed.

The life of the ege, in those races which have but one generation each
year, has three phases, the first lasting about three months, full of
activity; the second lasting from about October to the middle of Febru-
ary, one of inactivity, in which there are no signs of life; the third from
the middle of February to the moment of hatching, in which the vital
activity recommences, and the germ begins to organize as soon as the
temperature rises a little above 50° F. The measure of the activity
of the egg, in this stage, 1s the measure of its danger, for any sudden
change of temperature would injure or destroy the delicate embryo,
or cause the larva to be born before its food was ready. To guard
against such accidents, eggs must be wintered in a high region or ina
refrigerator at a uniform temperature of about 35- F., from December
15, until the mulberry begins to bud or until hatchings are desired.
There should always be good ventilation, the air should not be moist,
and great care must be taken to keep the eggs out of the reach of mice
and insects.

Natural hatchings are almost always irregular, extending over eight
or ten days, thus multiplying the divisions and rendering the rearing
difficult and costly; hence, the necessity for artificial incubation.

Eighteen days before the time decided on for the hatching, spread
out the eges in thin layers in the incubating room er incubator. The
temperature should be 55° F.

i il

HATCHING SILKWORM EGGS. 15

From the fourth day on, gradually increase the temperature two
degrees in twenty-four hours until 73° F. is reached, when, at this
uniform temperature, hatchings will occur in ten days on an average.
This period, however, varies from eight to fifteen days, according to
race, the cold supported during the winter, the first grade of heat, and
the highest during the incubation, and the number of days taken to
pass through these two grades of heat; and also according to the
humidity. To obtain a good and complete hatching, a slight humidity
is necessary, especiaily during the last four or five days. To secure
this keep an open vessel of water near
the fire, or sprinkle the floor with water
occasionally.

The temperature may be raised during
the hatching to 75° F., but sudden changes
of heat must be avoided, and, unless the
newborn worms can be kept in the same
temperature, it is dangerous to have the
maximum temperature of the incubator
so high.

It is better for the period of incubation
to be protracted than suddenly short-
ened. Holding the eggs at a certain tem-
perature, or slowly lowering the temper-
ature a little does no harm. When the
season is not propitious, the hatching
may in this way be retarded.

An incubating room is preferable, be-
cause it also serves for the first two stages
of the worms, but in small rearings an
incubator is more economical, both with regard to service and to fuel.

For a large quantity of eggs (5 to 10 ounces) a small incubator,
which is very much used in chemical laboratories to dry substances, is
recommended. Any ordinary tinsmith can make it. It consists of a
double case, cubical in form, with a zinc bottom. The space between
the outer and inner walls is filled with water. The front face of
the cube is furnished with a glass, so that the temperature within,
indicated by the thermometer hanging on the glass, may be seen with-
out the necessity of opening the incubator. There are two openings
below on opposite sides to allow the cold air to come in, and an opening
in the center of the top to permit the outward flow of the heated air.
Having filled the space between the walls with water, the incubator is -
placed on a support and heated by means of a gas or oil lamp to the
desired degree, and, by raising or lowering the flame, a constant or
progressive temperature can be maintained (fig. 7). A self-regulating

=

Fie. 7.—Hot waterincubator. (Redrawn
from Verson and Quajat. )

16 THE CULTURE OF THE MULBERRY SILKWORM.

incubator, such as is used to hatch chickens, would be more conven-
ient, but would cost more.

The whitening of the eggs denotes the near approach of the hatch-
ing. Double pieces of tulle or sheets of perforated paper sprinkled
over with finely cut-up white mulberry leaves should then be lightly
placed over the eggs to allow the outward passage of the worms as
soon as hatched. The object in employing two pieces of tulle or
paper is to prevent the unhatched eggs which cling to the sheet from
being removed with the newborn worms. This process must be
repeated daily during the hatching, the second sheet always being
renewed.

The duration of the hatching varies from three to five days, the eggs
hatching about as follows: During the first day, 5 per cent; during
the second, 33 per cent; during the third, 50 per cent; during the fourth,
5 per cent; during the fifth, 7 per cent.

Twenty-five grams of eggs will give about 17 grams of worms. In
small rearings most cultivators raise only the worms that are hatched
on the second and third days, to avoid the necessity of forming too
many classes. The worms must be classed according to the date of
birth, and the insignficant number hatched on the first and last days -
scarcely compensate for the trouble of rearing them. Different races
must also be reared separately.

Where several in one neighborhood are engaged in silk culture it
greatly reduces the cost to have all the eggs hatched in one incubator.
The person best acquainted with silk culture can undertake the incu-
bation, and distribute the young worms on the second or third days to
those who are to rear them. This is the plan adopted among the Italian
peasantry, the wife of the supervising farmer hatching the eggs for
whole villages.

THE REARING OF SILKWORMS.

Before entering into the details of a rearing some general directions
must be given concerning the rearing room—the heating, ventilation,
and disinfection.

GENERAL DIRECTIONS.

The place chosen for a rearing should be relatively high, and not
exposed to malaria or bad odors, and mulberry trees should grow
around it. Any room that can be properly heated and ventilated will
answer the purpose. An open fireplace is the best means of heating,
but is expensive, as much of the heat 1s lost. Hot-water pipes, such
as are used to heat a greenhouse, are good for a building specially
built for silkworm rearing. Iron stoves should not be used, unless
placed in an adjoining room with communicating pipes. Never employ
charcoal as fuel.

“I

THE REARING OF SILKWORMS. 1

Ventilation.

The domesticated worm should be surrounded continually by pure
air. The amount of carbonic-acid gas given out by the worms and
their attendants is very considerable; besides this, a quantity of dele-
terious gas is generated by the litter of the beds, and the lights and
fires consume a great deal of oxygen. Myriads of spores and germs
of organic life float in the air of the rearing room, and their influence
paralyzes the vital energy of the skin and of the organs of respiration,
on whose normal functions the robustness of the worm so much depends.
Hence, it is evident that the quantity of vitiated air which should be
expelled from the room requires the introduction of a large quantity
of fresh air. For this, a double system of ventilation is necessary,
which may be obtained by double openings in the windows, to allow
the heated bad air to pass out above and the cool fresh air to come in
below. To renew the air in every part of the room, and to avoid a
single and often violent current, there should be more than one win-
dow. An open fireplace is the best means of ventilation. When the
difference between the external and internal air is slight, or there is no
difference at all, artificial means must be used to create a current.
Light and frequent fires, or a burning lamp in the fireplace, or a
revolving fan, may be used to prevent stagnation of the air.

Disinfection.

Eight or ten days before introducing the worms into their quarters
all the shelves and implements should be washed in a solution of chlo-
ride of lime (11 pounds of chloride of lime to 88 quarts of water), or
in a solution of sulphate of copper (1 to 100 by weight).

When everything is in order—tools, perforated paper, material for
the worms to spin their cocoons on, ete., each in its own room—close
the doors and windows as tightly as possible and fumigate the rooms
with sulphur (11 pounds of sulphur to every 100 cubic yards of space).
To fumigate properly, powder the sulphur and place it in an earthen
or metallic vessel over a slow fire. The sulphur will gradually melt
and take fire. Place it immediately in the rearing room and leave it
there, with the doors and windows completely shut, for twenty-four
hours.

Nets should not be exposed to sulphur fumes, for this would soon
rot them, but should be washed in a solution of sulphate of copper, and
immediately afterwards in plain water.

Twenty-four hours after the fumigation the floors should be washed
with a solution of chloride of lime or sulphate of copper, and the walls
should be whitewashed with lime.

When dead worms are seen on the shelves, change the beds and create
in the rearing room sulphurous gas by burning a pound of sulphur
during six hours, or make a strong wood smoke, which is a good disin-
fectant and will not harm the worms.

16615—No. 39—03——2

18 THE CULTURE OF THE MULBERRY SILKWORM.

Wise precaution having been taken to destroy germs of disease in
the rearing room, the new-born worms may now be safely installed
there.
Space required.

The worms from 1 ounce of eggs should cover at birth 1 square yard.
Doubling this space on the fourth day, they would require 2 square
yards, and at their change of beds after molting, 4 square yards. By
the spacing of the third day of the second age, and the doubling of
beds preceding the second molt, they will need for the second age 8
square yards. For the third age 16 square yards will be required; for
the fourth age 32 square yards; and for the fifth age 60 square yards.
The more space that is accorded to the worms in their first ages, the
more robust they will be; and if the space can be tripled instead of
doubled during the fourth age, and for the fifth age be 70, 80 or 90
instead of 60 square yards, the harvest of cocoons could be raised from
60 kilograms to 70, 80, or 90 kilograms per ounce of eggs, the quality
of silk also being superior.

Temperature.

The silkworm is not a tropical insect, and attains its best develop-
ment between the temperatures of 68° and 77°F. It is safe to adopt
the mean between these two temperatures for the general rearing.
Each cultivator, however, may suit his convenience, remembering that
to fall below or to exceed the mentioned limits of heat is detrimental
to the worm, and will affect the quantity and the quality of its spinning.

From the second age the temperature should be from 70° to 72° F.
and should be kept as uniform as possible to the end of the rearing.
The time which elapses between one change and the following one may
be much shortened by raising the temperature and feeding oftener.
Such hasty rearings may be made in twenty two to twenty-four days.
They are, however, to be condemned, as contrary to the nature of the
silkworm. Meals following each other too closely can not be properly
digested, and are likely to cause disease. Besides, hasty rearing
require more labor, and the service must be kept up night and day.
As there 1s danger in too high a temperature, so there is danger tn
one that is too low (64° to 68° F.). A rearing that 1s too prolonged,
lasting over thirty-two days, is to be avoided to escape the heat of
June, under which the beds are more likely to ferment, causing disease;
the worms have less appetite and leave more leaf from one meal to
another; the changes are slower and less likely to occur instantane-
ously; and there is more risk of muscardine or calcino, a disease due
to a mold.

Both hasty and tardy rearings are, therefore, to be proscribed, and
those conducted in twenty-eight to thirty-two days alone are recom-
mended. This lapse of time permits the leaves of the mulberry to
acquire maturity, and the growth of the worm should be relative to
that of the leaf on which it feeds.

ee re

——. ss

THE REARING OF SILKWORMS. 19

THE FIRST AGE.

Hatchings usually occur early in the morning. The worms which
have crawled up through the holes of the tulle or paper to get food,
should not be removed before 10 a. m. to the laticed shelves covered
with paper to receive them. Each shelf must be marked with the
date of the birth of the worms put upon it, and care must be taken
to place on the same shelf only worms born on the same day, as a remu-
nerative rearing demands that such alone be raised together.

Should the hatching occur at 68° to 70° F., keep this temperature
during the first ages, and feed eight times during twenty-four hours; if
the temperature at birth is 75° to 77°., slowly diminish the tempera-
ture one or two degrees, and feed ten times in twenty-four hours.
_ The appetite of the worm increases or diminishes with the heat. The
second day, in case of the worms hatched at the maximum, adjust the
temperature to the degree proposed to conduct the rearing. In feeding
sprinkle finely cut up tender leaves frequently over the worms, and
toward the fourth day begin to regulate the number of meals so that
it will range from four to eight, according to the temperature. Before
cutting the leaf remove the stems. Distribute the leaf uniformly and
equally on the shelves, in order to prevent the worms from crowding
more on one side than another, and in order that they may be equally
nourished and make their changes simultaneously. Cut only a small
quantity of fresh leaf at a time, and keep the rest in jars or baskets
covered with a damp cloth. Never submerge the leaves in water. For
the first two or three ages, the white ungrafted mulberry is recom-
mended, it being lighter and more digestible for delicate worms.

It is well during the feeding to open the door and windows to insure
a good supply of freshair. After feeding, close the door and windows,
unless the day is warm, when they may be permanently left open, pro-
tected by curtains through which the air passes freely. The worms
should never be exposed to direct sunlight or to a strong current of
air, and during a thunderstorm the windows and doors should be closed.

Worms of the same age and development should be classed together.
To obtain this equalization, do not feed newborn worms until all that
have been hatched on one day have been removed to shelves, then give
a general meal. If at the end of two or three days it is noticed that
on certain shelves there are smaller worms than on others, in order to
_ allow the less developed worms to catch up with the more advanced
ones, place the former nearer the fire or on the highest shelves, where
the air is warmer, and give them one or two more meals than the larger
worms. For this reason it is well to have light movable shelves
(fig. 5).

Many cultivators of silkworms do not change the beds during the first
age, and it is not absolutely necessary, if the leaf has been well cleaned
of stems and very finely cut up, and, above all, if the airisdry. Change
of bed, however, must be made if the litter is damp, and the weather

20 THE CULTURE OF THE MULBERRY SILKWORM.

rainy, for the worms are going to molt in two or three days, and this
crisis should not occur in unhealthy conditions. It is always more
prudent to change beds on the fourth day, and is, therefore, advised.
The space occupied by the worms must be doubled when the change
of beds is made.

The bed on which the leaf and excrement accumulate is, perhaps,
the greatest source of danger to the worms. When there is not a free
circulation of air, gases are developed which almost always cause fer-
mentation, paving the way for future disease. Hence the necessity
for frequent change of beds. This is made in various ways. The
practice of doing this by hand is to be condemned because it consumes
too much time and is apt to injure the worms. Threadnets (fig. 8)
and perforated paper are the best means to employ. They save two-
thirds of the hand labor, and
thus allow beds to be oftener
renewed, which is a most im-
portant consideration. In the
first age tulle or mosquito net
may be employed instead of
nets or paper.

The manner of proceeding is
as follows: Place the last meal
at night on the nets and extend
them over the worms. By
morning the worms will have
mounted above the opening in
search of fresh leaf. Then lift
up the nets, beginning at the
top shelf, and place them on
clean shelves. Carefully de-
tach from the nets any portion
of the old bed, and, if the
worms are not molting, gather up the few worms that have remained
behind, and tenderly place them with the others. The change of beds
is thus rapidly effected with the least labor.

It is very important that the tension of the net be such as to prevent
the worms from being crowded together in the middle.

Perforated paper (fig. 9) is another means often used to effect change
of beds; but it does not allow the worms to mount with the same
facility. It is also apt to break when the worms become heavy, and
in many cases it has to be renewed annually, so, in the end it is no
cheaper than nets.

In changing beds, do not feed the worms that are first taken up until
all from the old bed have been removed; then give a general meal,
for all the worms born on the same day and forming one class should

Fic. 8.—Net used in changing beds.

THE REARING OF SILKWORMS. 21

have the same number of meals to-preserve their equality of growth,
which is necessary for a successful rearing.

Having adopted hours for feeding, these should be adhered to
throughout the rearing. When four meals are given, the best hours
are 5 to 6a. m., 10 to noon, 3 to 6 p. m., and 9 to 11 p. Dk

Toward the sixth day worms begin to eat less. This is a sign that
they are going to molt. Thenanother change of beds and doubling of
space are necessary.

The molt or change of the worm is easily recognized by a swelling
of the head, whitening of the skin, transparency of the body, anda
fixed position.

Nt

SS

y
‘\)

Fic. 9.—Perforated paper used in changing beds in the second and third ages.

To change the beds, proceed as before, only leave undisturbed on
the old beds the worms that are molting. When all the tardy worms
have been taken up and placed on shelves, give them frequent
sprinklings of finely cut up leaf to enable them to catch up with
the worms already molting. Diminish the feeding as the backward
worms begin to molt, and cease feeding entirely as soon as a single
worm comes out of the molt. Then wait twenty-four hours so that
the worms may be well over the change before giving a general meal.
In this way the equality of development necessary for a methodical
and successful rearing is maintained. A fast of twenty-four hours
will not hurt the advanced worms, while the extra feeding given to
the backward ones may enable them to become equal to the former.
The beds of the worms on the old litter may be changed when the
general meal is given.

29 THE CULTURE OF THE MULBERRY SILKWORM.

Many cultivators do not change the beds and double the space until
after the first molt, allowing all the worms to change in the same bed.
In this case, owing to the distribution of leaf for one or two days after
the molting has begun, the molting worms are covered by a more or
less thick coat of litter, and exposed to emanations of bad gases in a
critical period of life, which is likely to cause disease. Besides, in
the first age, the worms are so small that they are likely to be lost in
the litter, or to perish from suffocation. Hence, it is healthier to
change beds and double the space before the molt.

THE SECOND AGE.

The coming out of the molt is announced by the appearance of a
small triangular-shaped livid spot on the worm’s head, and the changed
skin is grayish in color. The worm takes several hours to recover
from a change; then it begins to search for food, which, however, as
before stated, must not be given before all the worms have reeovered
from the molt. Then a slight meal is given by means of perforated
paper or nets. The worms crawl up promptly and can be easily
gathered up and placed on fresh shelves.

If the two sets of worms recover from their molt at the same time,
they may be classed together; if there is a difference of a day, it will
be necessary to keep them separate throughout the rest of the rear-
ing, for the equality of age has disappeared, and, if they are put
together, the second change will not occur simultaneously for all the
worms, but will extend over several days, and occasion the greatest
trouble to reestablish the equality of size necessary for the best results.

In case no worms have had change of bed before the molt, do not
recommence feeding until the greater part of the worms are awake.
Do not fear that they will suffer from hunger. Then form a new
division of those still molting. It is frequently better to have two
divisions, but if, to simplify the work, but one is desired, by putting
the backward worms on the highest shelves, and feeding them oftener
than the advanced set, an equality may be reestablished.

Three days after the first molt the beds must be renewed, and at
the same time more space must be allowed the worms.

The second age is the shortest, being less by two or three days than
any of the others. Toward the fifth day of this age the worms begin
to molt again. Then act as before—that is, by aid of nets or per-
forated paper, remove the backward worms, in order to place them
elsewhere, and try by more heat and abundant: food to make them
catch up with the forward worms.

THE THIRD AGE.

The worms double their size in their third age; consequently the
space allotted to them must be doubled; that is, they must have 16
square yards instead of 8 square yards, as in the second age.

gn

——

Ee a en a ee ee

THE REARING OF SILKWORMS. y-P,

From the second to the third molt the same care is to be given as
has been prescribed for the first two ages, except that, if a small incu-
bating room has been used instead of an incubator, the worms must
now be transferred to a larger room to complete the rearing. Care
must be taken to heat this room the day before to 80° F., and the next
day lower the heat to the degree adopted for the rearing. Feed six
times daily either with whole leaves or leaves which are coarsely cut
up. For this as well as all the other ages the best rule to follow in
feeding is to give only a light sprinkling of leaf at the beginning and
end of each age, gradually increasing the ration up to the middle of
each age, and then diminishing to the time of a molt. The appetite
of the worm will serve asa guide. Give more or less leaf according
as the preceding meal has been more or less eaten. In this way leaf
will not be wasted and a large quantity of litter will not accumulate
under the worms, to their detriment.

Toward the sixth or seventh day of the third age, according to the
temperature, the worms begin to be languid and lose appetite, as
before, and are ready to make a third change. This is the most diffi-
cult of all and the one in which they seem to suffer the most. It is
also the period when diseases due to bad eggs or to a poor incubation
are developed. Excepting accidental diseases, a good result may gen-
erally be predicted if the third change is safely passed. With these
facts in view, from the beginning of the third age keep the worms
sparse on the shelves and see that the beds are dry and changed with
scrupulous care, the litter being far removed from the rearing room.
Avoid feeding with wet leaf, and to favor the molting raise the tem-
perature a degree. It will be noticed that the head and body of the
worm are more swollen than in other molts. It is this superabundance
of liquid that renders this molt so critical and necessitates a drier
atmosphere and a bed which is very dry and not apt to ferment.

The worms increase three times in volume after the third molt, and
must have space accordingly. They must be separated into three
divisions in the following manner: Instead of waiting, as in the first
two changes, until half of the worms have begun to molt, let down the
nets, or otherwise prepare for the removal of the backward worms
when one-third or even less of the worms show signs of molting.
About two-thirds will then crawl up on the fresh leaves, and must be
placed on a shelf where, after one or two meals, they proceed to molt,
being again divided after the first or second distribution of leaves,
according to the rapidity of the molting.

If only a few worms mount when the first division is made, the oper-
ation was delayed too long, and it is unnecessary to divide those first
taken up; butafter the change the division of those left on the old bed
can be made. To allow the worms to spread out, each division should
occupy but one-third of the shelf on which it is placed.

24 THE CULTURE OF THE MULBERRY SILKWORM.

THE FOURTH AGE.

When the worms are over their third molt they cease to be gray,
and take the characteristic color of their race. If they are too long
in molting it is because the temperature is too low; that is, below 68°
F. Increasing the heat a few degrees will excite the worms and enable
them to complete their change. After this the temperature adopted
for the rearing must gradually be resumed.

When all the worms have molted the third time a change of beds
must be made as in preceding ages. Do not be in haste to change.
Wait a few hours to permit the worms to recover their strength a
little. The recommendation to feed lightly at first applies especially
to the beginning of the fourth age.

If the outside temperature is normal, fires need not be kept up, and
the doors and windows may be left open, guarded by light curtains.
In this age the worms eat enormously and more help will be required
to gather and distribute leaf. Small branches of leaf may now be given
in place of whole leaves, and the number of meals may be reduced to
four, if the temperature is 68° to 70° F., at which temperature the
age will last nine days. If it is desired to reduce this age to seven
or eight days, raise the heat to 72° F., and give five or six meals daily.
Should change of weather retard the growth of the mulberry trees, and
temporarily cut off the supply of leaf, adapt the rearing to such a con-
tingency by lowering the temperature slowly to 66° or 68° F., and giv-
ing only three or even two meals daily. Then, when leaf is obtained,
gradually raise the temperature to the degree adopted for the rearing.

During the fourth age four changes of beds are made, including the
one which follows the third molt. <A single division of the worms is
sufficient, which will be the last, and particular care must be taken to
divide the worms into two equal parts. For this, spread the nets or
perforated paper over the worms when half are molting and proceed
as before.

THE FIFTH AGE.

Do not be in haste to change beds as soon as the worms have molted.
This precaution is necessary to allow the new organs to acquire con-
sistency, and to prevent worms from being lost in the litter. Conse-
quently, wait several hours, and change beds after the second meal,
the first being only a slight sprinkling of leaves. Worms are not
strong enough immediately after a change to digest a heavy meal.

The space during this age should not be limited. See that between
two worms another could be easily placed. Experience has proved
that the harvest of cocoons is often in proportion to the space accorded
to the worms during this age.

Feed from four to six times daily, according to the temperature,

and spread the branches or leaves out regularly, not to form a mass.
For a simultaneous mounting into the brush all the worms should eat
an equal quantity of food.

+. “ b ih . .
Matt ye ee ee Pe ee

THE REARING OF SILKWORMS. 25

As ripe berries are very indigestible, and also cause beds to ferment,
care must be taken to shake the trees well before gathering the leaves,
and whatever ripe fruit remains must be taken off before feeding.

If possible, change beds daily, especially if more than five meals
are given, or if the weather is very warm and damp and there are
signs of disease.

The first five days after the change the worms grow enormously,
and it is very difficult to satisfy their appetite. At the end of this
time the body suddenly diminshes in circumference, the excrement,
formerly dry and firm, now becomes moist and soft, and the appetite
diminishes and becomes capricious. This state generally lasts three days,
then suddenly the worm ceases to eat, and tries to get away from its
food. It prolongs its head, and, changing its former lazy habit of
scarcely moving except to get food, runs about in every direction,
stopping from time to time, and moving its head (now transparent
gold or white, according to race) like a blind person seeking the way.

These signs indicate that the worm is hunting a convenient place to
spin its cocoon. The worm is now mature, and a spinning place
should be ready to facilitate its metamorphosis. The humidity, which
always exists at this time on account of the mass of litter, is especially
dangerous to the worms; and it is increased if the worms do not all
mature and mount at the same time, for those that remain below
are wet by the liquid dejections of those that are the first to mount.
For this reason do not put worms in the spinning place until they are
perfectly mature. They then mount, and crawl around some time
seeking a favorable place for their cocoons. Finding this they evacu-
ate their digestive canal, and begin to throw around them an irregular
net in which the cocoon spun later will be suspended.

PREPARATIONS FOR SPINNING.

A considerable loss may occur in the spinning place even when the
rearing has been most successful. To avoid such loss observe the fol-
lowing precautions: (1) Prepare the spinning place in time; (2) arrange
it so that the worms may regularly mount, and have abundant room;
(3) have it well made, yet economical; and (4) regulate the heat and
ventilate the room.

Any convenient dry bushy brush, odorless and free from gum, will
serve to construct the spinning place; or if such is not available, bun-
dles of straw, or shavings, or finely split wp wood may be substituted.
The best and most economical arrangement is small bundles of brush
or straw placed upright between the feeding shelves, in rows, about
16 inches apart. The bundles are cut a half inch taller than the space
between the shelves, and their tops are spread out to form arches, and
to allow the worms plenty of room to spin (fig. 10).

- Branches of elm, oak, birch, etc., are used to place the worms in the
spinning place. ‘These branches are spread over the shelves at the end

26 THE CULTURE OF THE MULBERRY SILKWORM.

of the fifth age. Very soon they will be covered with mature worms
which have ceased to eat, and are turning away from the mulberry.
In this way it is easy to select the worms that should be transferred.

If the worms are equally developed, in thirty or forty hours they
will be shut up in their cocoons. The few that remain behind should
be placed elsewhere; fed with fresh leaf on clean beds they will soon
catch up with the others.

The fifth day after the mounting the worms that have not begun to
spin should be placed in bundles of twigs and covered with straw or
leaves, or put in a basket of shavings, where they will be forced to spin.

The temperature
during the spinning
should be 75° F., and
the humidity through-
out the rearing about
65°. A good practi-
cal test of humidity is
a saucer of salt; when
the salt is moist, re-
duce the humidity.
Carefully avoid dis-
turbing the worms
while spinning, and
then, as during all the
FEE EEE EITC OIE MARES ages, keep the room
Fic. 10.—Arrangement of spinning places. (Redrawn from Pas- 9s quiet as possible.

aed The most scrupulous
cleanliness should always be observed, both with regard ‘to the quar-
ters and the attendants; to keep from raising dust, wipe the floor
with a damp cloth instead of sweeping it.

PREPARING COCOONS FOR THE MARKET. -

The transformation of the larva into the chrysalis is, according to
the temperature, completed in from seven to ten days from the time at
which the first worm begins to spin. The cocoons are then said to be
mature, and this is the best time to gather them. If gathered earlier,
the producer will run the risk of having his cocoons rejected in the
market; and if later, he wili sustain a very sensible loss in their
weight, as they grow lighter from the time of their maturity until the
moth comes out. The best authority estimates the minimum loss as
4.1 per cent, and the maximum as 23.3 per cent. To avoid the risk
of soiling them, gather the cocoons from the lowest shelf up. They
may be freed from the web or floss by a very simple instrument
(fig. 11) or by hand.

After the removal of the web the cocoons are sorted into three
classes: (1) The perfect, (2) the double, and (8) the defective or

ae ee

PREPARING COCOONS FOR MARKET. 27

spoiled. They are then spread out in 4-inch layers, on clean shelves,
in an airy, dry room, not exposed to sunlight, and very carefully
guarded from rats, mice, and insects. The defective and discolored
ones are put in a separate room.

The thread of a cocoon is continuous with that of the web, and
diminishes in diameter within. Its length varies from 1,200 yards to
1,600 yards, and its value accordingly. Different races, sexes, and
conditions of rearing often produce notable differences in weight of
cocoons. Thus the weight may vary
from 155 to 320 cocoons to the pound
(340 to 700 to the kilogram).

Often two or more worms are in-
closed in the same cocoon. Cocoons
formed from such collaboration are
larger than single ones, irregular in
form, and cottony in texture. They
can not be unreeled, and consequently
are far less valuable than single ones.

The proportion of silk in a cocoon
varies according to the race and the régime to which the worm has
been subjected. The average normal cocoon at the time it is sold is
thus composed:

Fic. 11.—Device for removing floss from
cocoons. (Redrawn from Nenci.)

Per cent.
panne pete a Aer. eis PRUE ee) Aa) eben s oe e 68. 2
ernare wea eae asus. Lege Otis he Leb eke co ctd. -. Jen Rk 14.3
US OS See ek eee Con ns le a es oe ee ee i OMe eee 7
EE Se a ee See Oe eee ere ree eee ee 16.8

If the cocoons are not sold as soon as gathered, the chrysalides
should be killed without delay unless they are to be reserved for
reproduction. Otherwise the moths may pierce the cocoons, thus
rendering them unfit to be reeled.

The chrysalides are usually killed either by heat or suffocation.
The means most commonly employed are (1) the heat of the sun; (2)
hot dry air in a stove; (3) hot humid air in a stove; (4) steam; (5) oil
of turpentine; (6) carbon bisulphid or some other gas. Probably the
best of these means are steam at a temperature not above 212° F.
applied without pressure, or hot damp air at a temperature of 196> F,

The killing of the chrysalides is an important operation and one
requiring care and judgment. If some are left alive, the moths will
issue, thus rendering the cocoons of little value. On the other hand,
if the operation is continued too long, the silk may be injured. The
best methods are those in which the heat is carefully controlled and
excessive dryness is avoided.

The following is a very simple and easy way to destroy the chrysa-
lides by the use of steam:

Place a cauldron of water on a stove. When boiling begins set over the cauldron
a white hollow wooden cylinder, about 3 feet high and 2 feet in diameter, with

28 THE CULTURE OF THE MULBERRY SILKWORM.

a perforated bottom and open at the top. Arrange in this cylinder round baskets
three-fourths filled with cocoons; then cover the cylinder with a perforated lid. In
about thirty minutes the operation will be completed, after which remove the
cylinder, take out the baskets, and spread out the cocoons to dry before storing, to
prevent them from spoiling.

Mr. T. A. Keleher of this office has adopted the following plan:

The cocoons are placed in an air-tight box of about 24 cubic feet capacity; about
half an ounce of bisulphid of carbon in a small dish is placed in the box and left
over night. It is best to open one or two of the cocoons to find if the chrysalides
are dead; if not the operation must be repeated. Care should be exercised that
no fire of any kind be brought into the vicinity during this operation as the bisul-
phid of carbon is very inflammable.

In shipping cocoons care must be taken to pack them in baskets or
cases permeable to air, but sufficiently close to keep out rats and mice,
which are very destructive to cocoons.

DISEASES OF SILKWORMS.

In every successful rearing of an ounce of eggs about 40,000 worms
are hatched, and 30,000 succeed in spinning cocoons. The rest either
die from casual wounds or from diseases incidental to restricted action.
But sometimes whole chambers are destroyed by hereditary and con-
tagious diseases, and it is of supreme importance to cultivators to learn
how these scourges may be avoided. |

In this limited treatise only a bare mention can be made of the most
fatal diseases and of the necessary precautions to be taken to guard
against them. ‘The general cause of disease is the domestication of
the worm. By using good eggs, however, and following the methods
which are actually employed by successful rearers, remunerative results
are usually obtained. ‘To obtain good eggs it is necessary to adopt new
methods. These are chiefly such as involve the use of the microscope.

Among the many diseases of silkworms, the principal ones are:

Pebrine, flacherie or flaccidity, gattine or macilenza, calcino or mus-
cardine, and grasserie.

PEBRINE.

This disease was first noticed in epidemic form in France in 1845.
Since then it has appeared in Italy, Spain, Portugal, Turkey, Turkes-
tan, the Caucasus, Kashmir, China, and Japan, Cheeta to destroy
the silk industry.

Between 1833 and 1865 the annual crop of cocoons in France was
reduced by pebrine from 57,200,000 pounds to 8,800,000 pounds. No
remedy has been found for the disease, but the Pasteur microscopical
selection of eggs, insuring the birth of healthy worms, is a sure prevent-
ive. The universal adoption of this method has made pebrine almost
a thing of the past; and following Pasteur’s line of research, means
have now been discovered for avoiding every kind of silkworm disease.

Worms affected with pebrine develop slowly, irregularly, and very
unequally. Black spots are the most marked outward characteristics

—- 2

=——

—

i gd

DISEASES OF SILKWORMS. 29

of the disease; the internal signs are oval corpuscles only visible through
the microscope.

Worms healthy born may contract pebrine during life, but this may —
not prevent their spinning, as the disease does not reach its climax
before the chrysalid or moth stage, and in its incipiency the worm is
strong enough to spin, though the moth will produce diseased eggs.
Hence the necessity of repeating the microscopical examination for
each generation of worms.

Pebrine is not always visible,
and when latent induces other
diseases. When only one crop
of cocoons is made annually, it
is comparatively easy to resist
pebrine, as the germ of it, out-
side of an egg, retains its vitality
not longer than seven months.
The disease takes thirty days to
develop; therefore, if worms
from pebrinized eggs can be
made to spin within twenty-
five days after hatching, they
may yield a fair harvest of
cocoons. In any case, however,
it is only safe to use pure eggs,
as pebrine, even in undeveloped
stages, renders the worm more
liable to contract all other dis.
eases.

FLACHERIE, OR FLACCIDITY.

This is now the most dreaded
disease among European. silk-
worms. In general, worms are
struck with it after their fourth
molt, when they are mature, or Fig. 12.—Worms affected with flacherie dying in the
even while spinning (fig. 12). oe ge ty te

Without any apparent cause, they begin to languish, then remain
completely still, and shortly die. They blacken after death (tig. 13),
and give out a disagreeable odor. Often entire chambers perish ina
day. Again, the progress of the disease may be slow, the worms even
spinning their cocoons, but, dying in the chrysalid state, they putrify
and soil the cocoon, thus greatly diminishing the value of the harvest.
Flacherie is but another name for indigestion. Pasteur and many
other scientists assert that flacherie is due to ferments and vibrioni
developing in the intestinal canal of the worm; other authorities main-
tain that the disease may exist independently of these. However, as

30 THE CULTURE OF THE MULBERRY SILKWORM.

these micro-organisms, in the majority of cases, play a prominent part
in the development of flacherie, it is well to guard against them.

The principal causes of flacherie are: (1) Eggs being spoiled
through careless preservation; (2) hereditary tendency; (83) overfeed-
ing of worms; (4) wet, sweating, dewy, and fermented leaf; (5) leaf
submerged in water or full of mud; leaf from a new plantation or
from a shaded spot, coarse leaf, or change of leaf; (7) lack of ventila-
tion; (8) excessive heat; (9) dust; (10) keeping worms too thick on
trays; (11) accidental deaths of worms from injuries, these putrefy-
ing, and the ferments thus
created being communi-
cated to other worms; (12)

debility.
Fic. 13.—Worm which died of flacherie, putrefying after >
death. (Redrawn from Pasteur. ) If these

causes are

avoided, flacherie is not
likely to invade a rearing. To prevent contagion eggs should be
dipped in a solution of sulphate of copper before being incubated;
and in cleaning shelves and nets, wherever a dead worm is seen,
powdered sulphate of lime or copper should be applied.

Unlike the corpuscles of pebrine, the microscopic organisms, which
are probably the immediate cause of flacherie, remain alive from one
year to another, and the dust of a rearing room may contain them in
considerable quantities and become the means of infection. Hence, in
cases of flacherie, immediately after the rearing, the walls, shelves,
and all the implements should be washed in a solution of chloride of
lime or some other germicide, and the room should be fumigated with
sulphur.

GATTINE.

The external signs of gattine are indifference to food, torpor, dysen-
tery, and emaciation. It attacks the worm in the first ages, and is
especially manifested after a molt. Some-
times it is associated with flacherie, and, in
its incipient stage, is confounded with this
disease. Later the worm becomes extra- Wis
ordinarily emaciated and sufficiently tran- rye 14.—Worm emaciated by gattine
sparent to be mistaken for a mature larva. oa Aan ad HIE ECE
The hooks of the prolegs are lengthened
out and strongly attach the worm to whatever it touches. Meanwhile
torpor creeps on and soon ends tts life (fig. 14).

Worms having flacherie or gattine do not always die before mount-
ing into the brush, and if the disease has not entirely invaded the
organism they may even arrive at spinning. But instead of mounting
with the promptness and rapidity of healthy worms, they stop hesi-
tatingly at the base of the brush, then begin slowly to mount, stopping
on the first little twigs and distending themselves as though asleep,

DISEASES OF SILKWORMS. 31

sometimes with the head turned towards the base. Again, especially
in case of gattine, the worm wanders restlessly here and there, seek-
ing as 1t were power to eject the silky matter, but too impotent to do
more than throw out a scanty thread to weave a web or veil of a cocoon,
in which it generally falls and dies.

Eges free from disease and capable of resistance to disease are the
prime requisite in guarding against flacherie and gattine. The moment
some deaths are noticed, proceed as follows: (1) Change beds imme-
diately, briskly shaking the worms; (2) place the worms on disinfected
shelves; (3) burn the diseased and suspected worms that do not mount
on fresh beds; (4) if possible move the whole rearing to another room
previously aired and disinfected, and also aired after disinfection; (5)
do not feed during the three or four hours in which the change is
being made; (6) keep up a little wood smoke in the room; (7) give a
few scanty meals of light leaf; and (8) diminish the temperature a
little.

CALCINO, OR MUSCARDINE.

This disease, at first, has no visible appearance, but by degrees the
vitality of the worm is impaired, and it eats and moves slowly. The
body turns rose-colored or red, beginning with the stigmat 1, and then
contracts and loses its elasticity, after which the
worm stands still as though paralyzed, and finaly
dies 20 to 80 hours from the appearance of the
first symptoms. After death the body dries up
and is covered with a white efflorescence, causing
it to look like a stick of white chalk (fig. 15):
hence the name of the disease.

Calcino is caused by a mold or minute fungus.
There are two varieties of this fungus: Botrytis
bassiana and LB. tenella. They both attack the
worm in the same way. The spores of the mold
by chance get on the body of the worm when it is — ye. 15.—calcinated worm.
in a molting condition, and there take root, pene- —_ (Redrawn from Verson
trating below the skin. The thread-like mycelium ee
ramifies until it fills the entire body. Later some of the branches
fructify on the surface, and the fruit bursting envelopes the worm
with innumerable spores resembling a white powder.

Each spore is capable of settling on a molting worm and giving it
calcino, hence the necessity of taking steps to avoid contagion. Cal-
cino is more contagious than other silkworm diseases. Darkness,
stagnant air, dirt, warmth, and moisture are the five things that favor
mold, and caleino is due to a mold. :

The chief cause of the disease is neglecting to change the beds and
keeping litter in and around the room. When only one or two worms

32 THE CULTURE OF THE MULBERRY SILKWORM.

have died from calcino all the shelves should at once be cleaned and
divested of dead worms. The floor should be washed with a solution
of sulphate of copper (1 to 200 by weight), and a pound of sulphur
should be burned, or a strong wood smoke created in the room, which
should then be shut up five or six hours, after which the worms should
be fed. Should any worms die the next day the beds should again
be changed and an ounce of sulphur burned. The quantity of sulphur
fumes that would kill rats, bats, and lizards and even human beings
does no harm to silkworms. No hesitation, therefore, need be felt in
fumigating the rearing room with sulphur; but eggs and thread nets
must not be subjected to sulphur fumes. Silkworms affected with
calcino die before the moth stage; therefore, it is impossible for the
disease to be hereditary. But loose spores of the mold creating the dis-
ease may get on healthy eggs. These may be washed off by a good
bath of fresh water. Some recommend a bath with a solution of sul-
phate of copper (one-half per cent of copper). In cases of calcino the
room should be disinfected immediately after the cocoons are gathered
and the paper and brush used should be burned.

As calcino is never due to infected eggs no attention need be paid

to the presence of spores of the Botrytis in the microscopic examina-

tion to select eggs.
GRASSERIE.

Silkworms having this disease become restless, bloated, and yellow.
If punctured they exude a purulent matter full of minute polyhedral,
granular crystals.

Grasserie is neither hereditary nor contagious. Unlike pebrine,
flacherie, and calcino, it is not caused by microbes capable of multiply-
ing and creating plagues. (Grasserie does little harm to silkworms in
Europe, but in warm countries, as in Bengal, sometimes assumes an
epidemic form.

Worms first fed on mature leaf, and afterward on young leaf, are
apt to take grasserie. The propagation of large trees is the best means
of checking the disease.. The main cause of the sporadic appearance
of grasserie is mismanagement of the worms at the molting periods.
Feeding should not be stopped before all the worms have begun to
molt, and should not be recommenced until all the worms are well out
of the molt; otherwise they are likely to have grasserie. This disease
often leads to flacherie, and when it occurs in an exaggerated form
indicates latent pebrine.

O

ee ee

av d

: a a a 7 ee :