Insects frequently get stiffened before the entomologist has leisure to
get them set; and it usually happens that those sent home from foreign
countries have been ill set, and require to be placed in more
appropriate attitudes after they have fallen into the hands of the
scientific collector. They may be relaxed and made as flexible as
recently killed specimens by the following simple process, from which
they can receive no injury: Pin them on a piece of cork, and place the
cork in a large basin or pan of tepid water, and cover the top tight
with a damp cloth, taking care that it is sufficiently high not to
injure the insects. In most cases a few hours is sufficient to restore
them to their original flexibility, so that they may be easily put in
their proper positions. In some instances, three or four days are
necessary to relax them thoroughly, so as to set the wings without the
risk of breaking them; no force whatever must be used with any of the
members. When set up, after being relaxed, they must be treated in
exactly the same manner as recent specimens.
We must again caution the entomologist to be careful that he applies the
solution of corrosive sublimate to all his species, otherwise there is
little chance of their continuing long without being attacked by the
mite; they ought to be frequently imbued.
Mr. Waterton, who has studied deeply the subject of preserving animal
substances, and applied them not only in our own country, but also under
the influence of a tropical climate, makes the following observations on
the preservation of Insects: “I only know of two methods,” says he, “to
guard preserved insects from the depredations of living ones. The first
is, by poisoning the atmosphere—the second is, by poisoning the prepared
specimens themselves, so effectually that they are no longer food for
the depredators. But there are some objections to both these modes; a
poisoned atmosphere will evaporate in time if not attended to, or if
neglected to be renewed; and there is great difficulty in poisoning some
specimens on account of their delicacy and minuteness. If you keep
spirits of turpentine in the boxes which contain your preserved
specimens, I am of opinion that those specimens will be safe as long as
the odor of the turpentine remains in the box, for it is said to be the
most pernicious of all scents to insects. But it requires attention to
keep up an atmosphere of spirits of turpentine; if it be allowed to
evaporate entirely, then there is a clear and undisputed path open to
the inroads of the enemy; he will take advantage of your absence or
neglect, and when you return to view your treasure you will find it in
ruins. Spirits of turpentine poured into a common glass inkstand, in
which there is a piece of sponge, and placed in a corner of your box,
will create a poisoned atmosphere and kill every insect there. The
poisoning of your specimens by means of corrosive sublimate in alcohol,
is a most effective method. As soon as the operation is properly
performed, the depredating insect perceives that the prepared specimen
is no longer food for it, and will forever cease to attack it; but then
every part must have received the poison, otherwise those parts where
the poison has not reached will still be exposed to the enemy, and he
will pass unhurt over the poisoned parts till he arrives at that part of
your specimen which is still wholesome food for him. Now, the difficulty
lies in applying the solution to very minute specimens without injuring
their appearance; and all that can be said is, to recommend unwearied
exertion, which is sure to be attended with great skill, and great skill
will insure surprising success.”
I am convinced that there is no absolute and lasting safety for prepared
specimens in zoölogy from the depredations of insects, except by
poisoning every part of them with a solution of corrosive sublimate in
alcohol.
Mr. Waterton is of opinion that tight boxes with aromatic atmospheres
are not to be depended upon in the preservation of insects. He says:
“The tight boxes and aromatic atmospheres will certainly do a great
deal, but they are liable to fail, for this obvious reason, viz.: That
they do not render forever absolutely baneful and abhorrent to the
depredator that which in itself is nutritious and grateful to him. In an
evil hour, through neglect in keeping up a poisoned atmosphere, the
specimens collected by industry and prepared by art, and which ought to
live, as it were, for the admiration of future ages, may fall a prey to
an intruding and almost invisible enemy, so that, unless the solution of
corrosive sublimate in alcohol is applied, you are never perfectly safe
from surprise. I have tried a decoction of aloes, wormwood and walnut
leaves, thinking they would be of service on account of their
bitterness. The trial completely failed.”
Many entomologists are satisfied with possessing the insect in its
perfect or image condition. But it is exceedingly interesting to be able
to trace these through their different states of existence from the egg
to the perfect insect. Besides, we are certain to produce the insects in
the highest state of preservation when we breed them ourselves, and it
is besides very interesting to have the eggs of the different species as
well as the caterpillar and pupa.
=The Eggs of Insects.= The eggs of insects preserve their form and color
in a cabinet, in general, without much trouble. Swammerdam had a method
of preserving them when they appeared to be giving way. He made a
perforation within them with a fine needle, pressed out their contents,
afterwards inflated them with a glass blow-pipe, and filled them with a
mixture of resin and oil of spike.
=The Larvæ, or Caterpillars.= The easiest way of destroying the
Caterpillar is by immersion in spirits of wine. They may be retained for
a long time in this spirit without destroying their color.
Mr. William Weatherhead had an ingenious mode of preserving larvæ. He
killed the caterpillar, as above directed, and having made a small
puncture in the tail, gently pressed out the contents of the abdomen,
and then filled the skin with fine dry sand, and brought the animal to
its natural circumference. It is then exposed to the air to dry, and it
will have become quite hard in the course of a few hours, after which
the sand may be shaken out at the small aperture and the caterpillar
then gummed to a piece of card.
Another method is, after the entrails are squeezed out, to insert into
the aperture a glass tube which has been drawn to a very fine point. The
operator must blow through this pipe while he keeps turning the skin
slowly round over a charcoal fire; the skin soon becomes hardened, and,
after being anointed with oil of spike and resin, it may be placed in a
cabinet when dry. A small straw or pipe of grass may be substituted for
the glass pipe. Some persons inject them with colored wax after they are
dry.
=The Pupa.= When the insects have escaped from their pupa skin, the skin
usually retains the shape and general appearance it did while it
contained the insect. It is therefore ready for the cabinet, without any
preparation whatever. But if the animal has not quitted its envelope, it
will be necessary either to drop the pupa into warm water, or to heat it
in a tin case before the fire; the former mode, however, is the best,
and least liable to change the colors of the pupa.