If the moth is intended to be killed, and then placed in a cabinet, the use of sulphur must be avoided. It kills the moth, certainly; but it kills the colours also, and quite ruins its appearance. Sulphur is always a dangerous instrument in insect-killing, and should on no account be used. There are many ways of destroying insects humanely, and extinguishing their life as if by a lightning flash; but these modes vary according to the size, sex, and nature of the insect. Some of them I will here mention.
If the insect is a beetle, it may be plunged into boiling water, or into spirits of wine, in which a very little corrosive sublimate has been dissolved. Both modes will destroy the life rapidly, but the former is the better of the two. When walking in the fields or woods, a wide-mouthed, strong bottle, about half full of spirits of wine, is a useful auxiliary, as all kinds of beetles, and even flies and bees, can be put into it; and if dried in a thorough draught, will look as well as before. If this precaution be not taken, all the insects that have long hair, as the humble-bee and others, will lose their good looks, and their hair will be matted together in unseemly elf-locks.
Butterflies, and most of the Diptera, or two-winged flies, can be instantaneously killed by a sharp pinch on the under-surface of the thorax among the legs, as the great mass of nerves is there collected. Many people seem to fancy that the head is the vital part in an insect; and having pinched or run a pin through its head, they think that they have effectually slain the creature, and marvel much to see it lively some twenty-four hours afterwards.
Especially is this the case with the large-bodied moths, whose vitality is quite astonishing. You may even stamp upon them, and yet not crush the life out of that frail casket. If you drive the life out of one-half of the creature, it only seems to take refuge in the other; and then retain a more powerful hold, like a garrison driven into a small redoubt.
It is not at all uncommon to find one of these moths dead and dry as to its wings and limbs, which snap like withered sticks if touched, and yet with so much life in it as to writhe its abdomen if irritated, and to deposit its eggs just as if it were in full activity.
Indeed, so strong is this power that the creature seems to be gifted with a double life, one for itself and the other for its progeny. The former is comparatively weak, and but loosely clings to its home; but the latter intrenches itself in every organ, penetrates every fibre, and, until its great work is completed, refuses to be expelled. So, unless the entire mechanism of the insect be killed, the poor creature may live for days in pain.
Fortunately, there is a mode of so doing; and this is the way of doing it:—
Make a strong solution of oxalic acid, or get a little bottle of prussic acid—it is the better of the two, if you have discretion as beseems a naturalist. Also make a bone or iron instrument, something like a pen, but without a nib. Dip this instrument into the poison as you would a pen, and then you have a weapon as deadly as the cobra’s tooth, and infinitely more rapid in its work. Now hold your moth delicately as entomologists hold moths, near the root of the wings. Keep the creature from fluttering; plunge the instrument smartly into the thorax, between the insertion of the first and second pair of legs; withdraw it as smartly, and the effect will be instantaneous. The moth will stretch out all its legs to their full extent; there will be a slight quiver of the extremities; they will be gently folded over each other; and you lay your dead moth on the table.
The reason of this rapid decease is of a twofold nature.