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 zoology 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 Larvae, 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 larvae. 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.