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.
METHOD OF BREEDING INSECTS.
Breeding Cages. These must be made of oak, or other hard wood, as pine is apt to kill the caterpillars from its strong smell of turpentine. The best form for these is represented in Fig. 32. The sides and front are covered with gauze; a is a small square box, for the reception of a phial of water, for placing the stalks of plants in, on which it is intended the caterpillars are to feed. The most convenient size for a breeding cage is eight inches in breadth, four deep, and one foot in height. It is not proper to place within a cage more than one species of caterpillar, as many of them prey upon each other. Indeed, animals of the same species will devour each other if left without food. The caterpillars of insects, for the most part, will only eat one particular kind of food, so that it is better to have no more than one sort in a cage.