_General Directions._--The importance, even to the mere collector, of
rearing insects to obtain specimens for the cabinet has been referred to
from time to time in these pages. The philosophic study of entomology,
however, requires much more than the mere collecting of specimens, and
one of the most profitable and, at the same time, most fascinating
phases of the study relates to the life-history and habits. In no branch
of natural history are biologic studies more easily carried on, or the
biologic facts more remarkable or interesting. The systematist by such
study will be saved from the narrow and hair-splitting tendencies which
study of slight difference of characters tends to, while to the economic
entomologist it is most essential.
In the rearing of insects success will be attained in proportion to the
extent to which the conditions of nature in the matters of temperature,
moisture, food-supply, and conditions for pupation, are observed.
"In the hands of the careful breeder an insect may be secured against
its numerous natural enemies and against vicissitudes of climate, and
will, consequently, be more apt to mature than in a state of nature. The
breeding of aquatic insects requires aquaria, and is always attended
with the difficulty of furnishing a proper supply of food. The
transformations of many others, both aquatic and terrestrial, can be
studied only by close and careful outdoor observation. But the great
majority of insect larvae may be reared to the perfect state indoors,
where their maneuverings may be constantly and conveniently watched. For
the feeding of small species, glass jars and wide-mouthed bottles will
be found useful. The mouths should be covered with gauze or old linen,
fastened either by thread or rubber, and a few inches of moist earth at
the bottom will furnish a retreat for those which enter it to transform
and keep the atmosphere in a moist and fit condition.
_The Breeding Cage or Vivarium._--"For larger insects I use a breeding
cage or vivarium which answers the purpose admirably. It is represented
in figure 123, and comprises three distinct parts: First, the bottom
board _a_, consisting of a square piece of inch thick walnut with a
rectangular zinc pan _ff_, 4 inches deep, fastened to it above, and with
two cross pieces _gg_ below, to prevent cracking or warping, facilitate
lifting, and allow the air to pass underneath the cage. Second, a box
_b_ with three glass sides and a glass door in front, to fit over the
zinc pan. Third, a cap _c_, which fits closely on to the box, and has a
top of fine wire gauze. To the center of the zinc pan is soldered a zinc
tube _d_ just large enough to contain an ordinary quinine bottle. The
zinc pan is filled with clean sifted earth or sand _e_, and the quinine
bottle is for the reception of the food plant. The cage admits of
abundant light and air, and also of the easy removal of excrement or
frass which falls to the ground; while the insects in transforming enter
the ground or attach themselves to the sides or the cap, according to
their habits. The most convenient dimensions I find to be 12 inches
square and 18 inches high: the cap and the door fit closely by means of
rabbets, and the former has a depth of about 4 inches to admit of the
largest cocoon being spun in it without touching the box on which it
rests. The zinc pan might be made 6 or 8 inches deep, and the lower half
filled with sand, so as to keep the whole moist for a greater length of
time."
The sand or earth in the zinc pan at the bottom of the breeding cage
should be kept constantly moistened, and in the case of hibernating pupae
the constant adding of water to the top of the earth or sand causes it
to become very hard and compact. To overcome this objection it was
suggested in the _Entomologists' Monthly Magazine_ for June, 1876, page
17, that the base should be made with an inner perforated side, the
water to be applied between it and the outer side, and I have for some
years employed a similar double-sided base, which answers the purpose
admirably (See Figure 124). It is substantially the same as that made
for the Department by Prof. J. H. Comstock in 1879. It consists of a
zinc tray _a_, of two or three inches greater diameter than the breeding
cage, which surrounds the zinc pan proper containing the earth, and the
tube _d_ for the reception of the food-plant. The lower portion of the
inner pan _b_ is of perforated zinc. Zinc supports, _c c_, are
constructed about halfway between the bottom and the top of this pan, on
which the breeding cage rests. In moistening the earth in the cage,
water is poured into the tray, which enters the soil slowly, through the
perforations in the zinc pan. I have found this modification of very
decided advantage and use it altogether in the work of the Division, and
heartily recommend it.
[Illustration: FIG. 123.--Insect breeding-cage or vivarium.]
The base of the vivarium or breeding cage should never be made of tin,
but always of zinc. If made of tin, it will soon rust out. Galvanized
iron may be used in place of the zinc, and will doubtless prove equally
satisfactory.
"A dozen such cages will furnish room for the annual breeding of a great
number of species, as several having different habits and appearance,
and which there is no danger of confounding, may be simultaneously fed
in the same cage. I number each of the three parts of each cage to
prevent misplacement and to facilitate reference, and aside from the
notes made in the notebook, it will aid the memory and expedite matters
to keep a short open record of the species contained in each cage, by
means of slips of paper pasted on the glass door. As fast as the
different specimens complete their transformations and are taken from
the cage the notes may be altered or erased, or the slips wetted and
removed entirely. To prevent possible confounding of the different
species which enter the ground, it is well, from time to time, to sift
the earth, separate the pupae and place them in what I call 'imago
cages,' used for this purpose alone and not for feeding. Here they may
be arranged with references to their exact whereabouts.
[Illustration: FIG. 124.--Improved base for breeding-cage (original).]
"A continued supply of fresh food must be given to those insects which
are feeding, and a bit of moist sponge thrust into the mouth of the
bottle will prevent drowning, and furnish moisture to such as need it.
By means of a broad paste brush and spoon the frass may be daily removed
from the earth, which should be kept in a fit and moist
condition--neither too wet nor too dry. In the winter, when insect life
is dormant, the earth may be covered with a layer of clean moss, and the
cages put away in the cellar, where they will need only occasional
inspection, but where the moss must nevertheless be kept damp. Cages
made after the same plan, but with the sides of wire gauze instead of
glass, may be used for insects which do not well bear confinement
indoors, the cages to be placed on a platform on the north side of a
house, where they will receive only the early morning and late evening
sun."
_Detailed Instructions for Rearing._--In the rearing of insects every
worker will develop a number of methods of value, and it is only by
careful study and comparison of the experiences of all that the best
system can be elaborated. For this reason I have, in what follows,
quoted, in a more or less fragmentary way, the experiences of different
entomologists.
As is remarked by Miss Murtfeldt, in an interesting paper read before
the Entomological Club of the American Association for the Advancement
of Science, August 20, 1890, "there is a great individuality, or rather
specificality, in insects, and not infrequently specimens of larvae are
found for which the collector taxes his ingenuity in vain to provide.
Not the freshest leaves, the cleanest swept earth, or the most
well-aired cages will seem to promote their development."
The greatest care and watchfulness, therefore, are necessary to insure
success in the rearing of larvae. In many cases such larvae can only be
successfully reared by inclosing them in netting on their food-plant out
of doors. It is a frequent device of Lepidopterists also to inclose a
rare female in netting placed on the food plant of the species, where
the male may be attracted and may be caught and placed in the bag with
the female, when copulation usually takes place successfully, or a male
may be caught in the field and inclosed with such female. Mr. W. H.
Edwards, where the plant is a small one, uses for this purpose a
headless keg covered at one end with gauze, which he places over the
plant inclosing the female.
Mr. James Fletcher, of Ottawa, Canada, one of our most enthusiastic
rearers of insects, has given some details of his methods in a recent
very interesting account of "A Trip to Nepigon." One style of cage used
by him in securing the eggs of large Lepidoptera "is made by cutting two
flexible twigs from the willow or any other shrub and bending them into
the shape of two arches, which are put one over the other at right
angles and the ends pushed into the ground. Over the penthouse thus
formed a piece of gauze is placed, and the cage is complete. The edges
of the gauze may be kept down either with pegs or with earth placed upon
them." This kind of cage is used for all the larger species which lay
upon low plants. The species which oviposit on larger plants or trees
are inclosed in a gauze bag tied over the branch. This is applicable to
insects like _Papilio_, _Limenitis_, _Grapta_, etc. Care must be taken,
however, that the leaves of the plant inside the net are in a natural
position, for some species are very particular about where they lay
their eggs, some ovipositing on the top of the leaves, others near the
tip, and many others on the under surface. "When a bag made beforehand
is used, the points must be rounded, and in tying the piece of gauze
over the branch care must be taken to pull out all creases and folds, or
the insect will be sure to get into them and either die or be killed by
spiders from the outside of the bag. It is better to put more than one
female in the same cage. I have frequently noticed that one specimen
alone is apt to crawl about and settle on the top of the cage, and not
go near the food plant. When there are two or three they disturb each
other and are frequently moving and falling on the food plant, when they
will stop for a moment and lay an egg. A stubborn female of _Coleus
eurytheme_ was only induced to lay by having a male placed in the cage
with her, and by his impatient fluttering and efforts to escape she was
frequently knocked down from the top, and every time she fell upon the
clover plant beneath, she laid an egg before crawling to the top again."
Some insects, even with all care in making their surroundings as natural
as possible, will persistently refuse to lay. Mr. Fletcher has
successfully obtained eggs from some of these by a method which he says
one of his correspondents styles "Egg-laying extraordinary." It consists
simply in "gently pressing the abdomen of a female which has died
without laying eggs, until one and sometimes two perfect eggs are passed
from the ovipositor." Mr. Fletcher has secured a number of eggs from
rare species in this way, and successfully reared the larvae. The
following directions for obtaining the eggs and rearing the larvae of
Lepidoptera, given in this paper by Mr. Fletcher, are excellent, and I
quote them entire:
"There are one or two points which should be remembered when obtaining
eggs and rearing larvae. In the first place, the females should not be
left exposed to the direct rays of the sun; but it will be found
sometimes that if a butterfly is sluggish, putting her in the sun for a
short time will revive her and make her lay eggs. Confined females,
whether over branches or potted plants, should always be in the open
air. If females do not lay in two or three days they must be fed. This
is easily done. Take them from the cage and hold near them a piece of
sponge (or, Mr. Edwards suggests, evaporated apple), saturated with a
weak solution of sugar and water. As soon as it is placed near them they
will generally move their antennae towards it, and, uncoiling their
tongues, suck up the liquid. If they take no notice of it the tongue can
be gently uncoiled with the tip of a pin, when they will nearly always
begin to feed. It is better to feed them away from the plant they are
wanted to lay upon, for if any of the sirup be spilled over the
flowerpot or plant it is almost sure to attract ants. I kept one female
_Colias interior_ in this way for ten days before eggs were laid. When
eggs are laid they should, as a rule, be collected at short intervals.
They are subject to the attacks of various enemies--spiders, ants,
crickets, and minute hymenopterous parasites. They may be kept easily in
small boxes, but do better if not kept in too hot or dry a place. When
the young caterpillars hatch they must be removed with great care to the
food plant; a fine paint brush is the most convenient instrument. With
small larvae or those which it is desired to examine often, glass tubes
or jelly glasses with a tight-fitting tin cover are best. These must be
tightly closed and in a cool place. Light is not at all necessary, and
the sun should never be allowed to shine directly upon them. If
moisture gathers inside the glasses the top should be removed for a
short time. Larvae may also be placed upon growing plants. These can be
planted in flowerpots and the young caterpillars kept from wandering
either by a cage of wire netting or, by what I have found very
satisfactory, glass lamp chimneys. These can be placed over the plant,
with the bottom pushed into the earth, and then should have a loose wad
of cotton batting in the top. This has the double effect of preventing
too great evaporation of moisture and keeping its occupants within
bounds. Some larvae wander very much and climb with the greatest ease
over glass, spinning a silken path for themselves as they go. When
caterpillars are bred in the study it must not be forgotten that the air
inside a house is much drier than it is out of doors amongst the trees
and low herbage, where caterpillars live naturally. The amateur will
require some experience in keeping the air at a right degree of moisture
when breeding upon growing plants. In close tin boxes or jars, where the
leaves must be changed every day, there is not so much trouble. An
important thing to remember with larvae in jars is to thoroughly wash out
the jars with cold water every day. If, however, a caterpillar has spun
a web on the side and is hung up to moult, it must not be disturbed. In
changing the food it is better not to remove the caterpillars from the
old food, but having placed a new supply in the jar, cut off the piece
of leaf upon which they are and drop it into the jar. If they are not
near the moult a little puff of breath will generally dislodge them.
Some caterpillars, as _Papilio turnus_, which spins a platform to which
it retires after feeding, can best be fed upon a living tree out of
doors, but must be covered with a gauze bag to keep off enemies. A piece
of paper should be kept _attached_ to each breeding jar or cage, upon
which regular notes must be taken _at the time_, giving the dates of
every noticeable feature, particularly the dates of the moults and the
changes which take place in the form and color at that time."
The necessity of outdoor work is further felt in the determination of
the facts in the life-history of some insects which have an alternation
of generations, as some Gall-flies (_Cynipidae_), and most Aphides. To
successfully study these insects constant outdoor observation is
necessary, or the species must be inclosed in screens of wire or netting
outdoors on their food-plant. Many insects which breed on the ground or
on low herbage may be very successfully watched and controlled by
covering the soil containing them or the plant on which they feed with a
wire screen or netting. The use of wire screens is also advisable in the
case of wintering pupae or larvae out of doors. Many species can be more
easily carried through the winter by placing them outdoors under such
screens during the winter, which insures their being subjected to the
natural conditions of climate, and then transferring them to the
breeding cage again early in the spring. This is advisable in the case
of Microlarvae and pupae. Species which bore in the stems of plants may be
easily cared for and leaf-mining and leaf-webbing forms can be secured
under screens or covers out of doors for the winter in sheltered
situations. Many species which, if kept in a warm room can not be
reared, will, if subjected to freezing weather under slight protection
in the open air, emerge successfully the following spring.
The greatest care is necessary in the breeding of Tenthredinidae, as most
of them transform under ground and are single brooded, the larvae
remaining in the ground from midsummer until the following spring.
Nothing but constant care in maintaining uniform moisture and
temperature of the soil will insure the success of such breeding. Some
species bore into rotten wood or the stems of plants to undergo their
transformations, as for instance the Dogwood Saw-fly (_Harpiphorus
varianus_). This species, unless supplied with soft or rotten wood in
which to bore, will wander ceaselessly round the cage, and in most cases
eventually perish.
Where a small room can be devoted to the purpose, an excellent wholesale
method of obtaining wood-boring insects (_Coleoptera_, _Lepidoptera_,
etc.) is to collect large quantities of dead or dying wood of all sorts
or any that indicates the presence of the early states of insects, and
store it in such apartment. The following spring and summer the escaping
insects will be attracted to the windows and may be easily secured. The
objection to this method is that, in many cases, it will be impossible
to determine the food habit of the insect secured, owing to the variety
of material brought together.
_The Root Cage._--For the study of insects which affect the roots of
plants a root cage has been devised by Prof. J. H. Comstock which is of
sufficient importance to warrant full description. It consists of a zinc
frame (Fig. 125_a_) holding two plates of glass in a vertical position
and only a short distance apart, the space between the plates being
filled with soil in which seeds are planted or small plants set. Outside
of each glass is a piece of zinc or sheet iron (_b_) which slips into
grooves and which can be easily removed. When these zincs are in place
the soil is kept dark.
The idea of the cages is, that the space between the glasses being very
narrow, a large part of the roots will ramify close to the surface of
the glass, so that by removing the zinc slides the roots may be easily
seen, and any root-inhabiting insects which it maybe desirable to breed
may thus be studied in their natural conditions without disturbing them.
Prof. Comstock has used this cage very successfully in studying the
habits of wire-worms, and its availability for many of the underground
insects, such as the Cicadas, root-lice, larvae, etc., is apparent. These
frames may be made of various sizes, to accommodate particular insects.
It will be of advantage in many cases, in order to secure the natural
conditions as nearly as possible, to sink the cage in the soil, and for
this purpose Prof. Comstock has had constructed a pit lined with brick
for the reception of his cages, and employs a small portable crane to
lift them out of the ground when it is desirable to examine them.
_Other Apparatus._--Much of the breeding of insects can be done with the
simplest apparatus, and for the rearing of Microlepidoptera,
Gall-insects, and the keeping of cocoons and chrysalides of small
species, nothing is more convenient than a medium sized test-tube, the
end of which may be plugged with cotton. I have recently successfully
carried over the winter the larva of _Sphecius speciosus_, which had
been removed early in the fall from its earthen pod or cocoon, the larva
transforming to a perfect pupa in the spring. In this case the test tube
was plugged with cotton and inserted in a wooden mailing tube to exclude
the light. Smaller jars with glass covers or with a covering of gauze
may be employed for most insects, with the advantage of occupying
comparatively little space and of isolating the species under study.
[Illustration: FIG. 125.--Root cage: _a_, frame with slide removed; _b_,
movable slide; _c_, top view (original).]
Long glass tubes, open at both ends, are useful in many other ways,
especially in the rearing and study of the smaller hypogean insects or
those which bore and live in the stems of plants. An infested stem cut
open on one side and placed in such a tube will generally carry any
insect that has ceased feeding, or any species like the wood-boring bees
which feed upon stored food, successfully through their transformations;
while root-lice may be kept for a lengthy period upon the roots in such
tube, providing a portion of the root extends outside of the tube and is
kept in moistened ground or water. In all such cases these tubes, with
their contents, should be kept in the dark, either in a drawer or else
covered with some dark material which can be wound around or slipped
over them, and the ends must be closed with cotton or cork.
The rearer of insects will frequently experience difficulty in carrying
his pupae through the winter, and, even though ordinary precautions are
taken, the mortality will frequently amount to 50 per cent of the
specimens. Mr. H. Bakhaus, of Leipzig, thus describes a device which is
substantially the base of the vivarium shown on page 114.
"The base consists of a round plate of strong zinc, with two vertical
rims, an inch high, placed one within the other, an inch apart, and
soldered to the basal plate so that the outer one is water-tight. The
inner rim must be perforated with small holes as close to the bottom as
possible. The space inside the inner rim must be filled with fine sand,
on which the pupae should be laid. The space between the two rims is then
filled with water, which, finding its way through the holes in the inner
rim to the sand, causes the necessary moisture. Over the whole is put a
bell-shaped cover of wire gauze, which must fit tightly over the outer
rim. In this receptacle the pupae remain untouched, and receive fresh
moisture, as above indicated, if required by the drying of the sand."
The hardy pupae of most Noctuids and Bombycids, as well as those of many
Rophalocera, may be handled with little danger, but other species, if
handled at all, or if the cocoons which they make for themselves are
broken, can seldom be reared. Constant precautions also must be
exercised in the care of the soil and the breeding cages. One of the
great drawbacks is the presence of mites and thread worms (Entozoons),
etc., which affect dying or dead pupae and larvae in the soil. They also
affect living specimens and are capable of doing very considerable
damage. To free the soil of them it is necessary at times to allow the
earth to become dry enough to be sifted, and then after removing the
pupae submit it to heat sufficient to destroy any undesired life there
may be in it.
_The Insectary._--Up to the present time the work of rearing insects has
been largely confined to the breeding cage and breeding jar, already
described, which have been kept in the rooms of the investigator. The
advantages of having a special building for this purpose are at once
apparent and need not be insisted upon. One of the best establishments
of this kind is that of the Cornell University Experiment Station, which
was fully described in Bulletin No. 3, of that station, November, 1888.
The Kansas Experiment Station has a similar building, and one has
recently been built for the use of the Entomological Division of the
United States Department of Agriculture. The insect-breeding house, or
insectary, should comprise a building having workrooms, or laboratories,
for microscopic and general work in the study and preparation of
specimens, and also a conservatory for the rearing of specimens and the
growth of plants, and, where applied entomology is concerned, special
rooms for the preparation and the test of insecticides. The building
proper should also have a basement storage room for hibernating insects.
The laboratory should be fitted with all the apparatus used in the study
of insects, including microscopes and accessories and a dark-room for
photographic purposes.