Enough has been said upon the best modes of catching insects:—I shall next attempt to give you some further instructions as to the most effectual one of destroying them when caught, and to point out how you are to proceed with them after they are dead. As I sufficiently rebutted the charge of cruelty in a former letter[1564], it will not be necessary to enter here into that subject.
I have before recommended to you the use of spirits of wine, and shall here repeat my recommendation; for after several years trial, I am of Böhm's opinion, who had tried it nine years[1565], that it is superior to any other method; particularly, because it not only effectually kills the insects, and they may be put together into it while you are collecting, if you have no reason for keeping them separate, of all sorts and sizes, in a wide-mouthed phial, without danger of their devouring each other: but when you come home wearied with a long day's hunt, you may let your insects remain in it without injury till the next morning. In collecting beetles abroad, when there is a want of store-boxes the readiest way is to put them into a wide-mouthed bottle or jar filled with any spirit, and send them home in it: some few may lose their colours, or become greasy; but in general they will receive little injury. This method saves room, and avoids the risk of breakage. The derangement which some hairy species sustain from this method may be readily repaired by brushing them with a dry camel's-hair pencil.
When you wish to take the insects you have immersed in spirits out of the phial, you must strain its contents through a piece of muslin, return the spirit into it for future use, and spread the insects separately upon blotting-paper, to absorb the moisture remaining about them. With regard to such as you have in boxes or phials without spirit, these must be immersed in a basin of boiling water. First empty into it the contents of your boxes, and next, those of your phials; giving each, before you take out the cork, a smart rap, that the insects adhering to the latter may drop to the bottom: or you may immerse the phial itself, with the cork in, which soon destroys them, and is the safest plan. This done, with a camel's-hair pencil or feather take them out of the water, lay them upon blotting-paper to dry, and put them by for a few hours till you have leisure to impale and set them.
Those insects that are caught by the forceps would for the most part escape you, were you to attempt to get them out before you had transfixed them. You must therefore do this while the leaves of the instrument are closed; and then opening them, and taking the pin by the point, the head will readily pass through the catgut; and thus you may safely take, and more effectually kill your specimen by pressing it as before directed. With respect to Lepidoptera, it is necessary to disable them while yet in the fly-net, immediately after their capture. To effect this, while one hand holds both the rods of the closed net, with the other stretch the gauze so as to confine your insect within a narrow space; bring its wings into an erect position, and prevent its fluttering: which being done, with your finger and thumb give its breast a strong pinch below the wings; and then unfolding your net, and taking it up by one of its antennæ, place it between the finger and thumb of your left hand, stick a pin through it, and deposit it in your pocket-box.
But though nipping the breast will kill many small Lepidoptera, the larger ones will live long after it; as will likewise many Neuroptera, Hymenoptera, and Diptera: and besides this, in some Bombycidæ the thorax presents a very conspicuous and interesting character, which renders it desirable, in order to avoid the damage or derangement occasioned by pressure, to transfix them without it. To dispatch these effectually, you will find the following apparatus very convenient. Fix in a small tin saucepan[1566] filled with boiling water, a tin tube consisting of two pieces[1567] that fit into each other; cover the mouth of the lower one[1568] with a piece of gauze or canvass, and place your insects upon it; then fix the upper one[1569] over it, and cover also the mouth of this with gauze, &c.; and the steam from the boiling water will effectually kill your insects without injuring their plumage. There is another more simple mode of doing this, the apparatus for which may be met with every where. Fix a piece or two of elder, willow, or any soft wood, with the bark on, across the bottom of a mug, and on this stick your impaled insects; invert the mug in a deep basin, into which pour boiling water till it is covered, holding it down with a knife, &c., that the expansion of the included air may not overturn it. In two minutes, or less, all the insects will be found quite dead, and not at all wetted. If the sticks do not exactly fit, they may be wedged in with a piece of cork. Professor Peck, who used to put minute insects into the hollow of a quill stopped with a piece of wood made to fit, killed them instantaneously by holding it over the flame of a candle.
Having killed your insects, your next object should be to prepare them for your cabinet. First, place by you a pincushion well stored with lace-pins of various magnitudes and lengths: for most insects those nearly an inch in length, for large ones, those that are thicker and longer, but for Lepidoptera, a stouter kind, as short whites, are best. Next, take the Coleoptera and Hemiptera that, as before directed, you have laid by on blotting-paper after immersion, and begin your operations, selecting the largest first. The pin should be stuck through the middle of the right-hand elytrum[1570], and about one third of its whole length should emerge above the insect. Some foreign collectors, probably having in view its more convenient examination with a microscope under the glass of a drawer, bring it nearer the head of the pin: while the English ones, on the contrary, studying the most ornamental position of their specimens, leave only enough of the point free to fix them safely in their drawers[1571]. Both these methods are open to objection. When the insect is too near the head of the pin, it is difficult to fix it in your cabinet without bending the wire; and there is danger, without great care, of injuring the specimen when you put it in or take it out. Again: When the legs of your insect rest on the surface they collect the dust and dirt, are very liable to be broken, and the length of the pin above it is inconvenient when you have occasion to examine any one under a lens. Lepidoptera, however, which are never thus examined, may always be transfixed in this way, which sets them off to the greatest advantage.
Some insects, especially of the beetle tribe, are so extremely minute that it is next to an impossibility to get a pin through them without injuring, and often destroying them. By using fine needles, or very slender pins manufactured on purpose, this difficulty might perhaps be surmounted; but the needles will be subject to rust, and the pins, I know by experience, cannot be fixed in cork without difficulty. For such minute insects, therefore, by far the best mode is to gum them on small pieces of card, which may be stuck upon a pin. Talc, which admits the underside of an insect to be seen through it, has been used for this purpose; and where you have only a single specimen, a thin small lamina of it would answer well; but ordinarily I should recommend the former mode. Your pieces of card, which must be small, may be either oblong and cut at the corners for neatness, with a couple of specimens gummed upon each, one on its belly and the other on its back; or you may cut little narrow card wedges, about four lines long and terminating in a point, upon which you may so gum your insects as to show the principal part of the under side, as well as the upper side of its body. Common gum-water made rather thin, with a very little glue mixed with it, will answer your purpose very well: it should be thinly spread on the card with a camel's-hair pencil, and then the insect placed upon it. With the same implement, if it has not been killed too long, before the gum is dry you may expand its antennæ, palpi, legs, and wings, &c. If you want to remove a specimen gummed on a card for any purpose, it is easily effected by plunging it into hot water.
Other insects may be transfixed through the thorax or upper side of the trunk; as also those Coleoptera, Orthoptera, and Hemiptera, whose wings you are desirous of expanding; only you should be careful that your pin passes through them behind the prothorax.
Having impaled your insects, the next thing to be done is to set them. The best time for doing this is not till they have begun to stiffen, but before they are become quite stiff. If attempted soon after they are killed, the parts, unless you keep them in the intended position by means of pins or braces, will not retain it; and if after they are become too stiff, they are liable to be broken. Not only should the antennæ and palpi be extended so as to be readily seen; but the legs, and often the wings, ought to be placed in their natural position; all of which tends much to the beauty of your specimens, and adapts them for more ready examination. But as this operation requires time, and beauty and regularity may be purchased too dear if at the price of hours called for by science, you may be left to your own discretion in this business, only you should always with a pin expand the antennæ and palpi if possible. You might, however, both save your time and have your insects neatly set, if you would take the trouble to instruct some acute and handy youth in your neighbourhood in the modus operandi, and devolve this department upon him: and as none are quicker and more expert in capturing insects than boys, he might also assist you in your hunting expeditions.
I do not mean, however, to leave you at liberty with regard to the setting of Lepidopterous insects, which not only have a much worse appearance than those of other Orders if their wings be not regularly and uniformly expanded, but require it for the proper display of their characters. The necessary apparatus consists of a piece of cork about nine inches long, four broad, and half an inch thick, which should be made perfectly smooth, with a piece of white paper pasted over it; and of several narrow slips of card or braces, tapering gradually to a point, of different lengths, from half an inch to two inches or more, with a pin fixed in each at the broadest end. Thus provided, you may proceed to action. But you must first decide whether, like the continental Entomologists, you will set your Lepidoptera horizontally; or, like the British, with their wings declining obliquely from the body. If you prefer the former method, the body must be let into a groove, and the wings expanded as flatly as possible, the anterior margin of the primary pair being brought forward so as to project beyond the head. But as this usually gives the insect an unnatural and formal appearance, I apprehend a man of your taste will prefer the mode adopted by your compatriots, the collectors of Britain, who in setting make the wings form an angle, varying according to the size and characters of the insect, with the body, and do not bring the anterior wings so forward. The wings of butterflies however, in order to appear at all natural, should be set more horizontally. Which fashion soever you prefer, the mode of operating is nearly the same; only that the English plan, except in the case of some large-bodied moths or hawk-moths, requires no groove in the setting-board. After you have stuck the insect upon the cork so as to bring its body close to its surface, stretch the anterior wing with a needle fixed in a handle, or a camel's-hair pencil, applied to the joint at the base, sufficiently forward, and then confine it by means of one of your card braces:—next, do the same by the opposite wing. Afterwards expand the posterior wings, which must not be separated from the anterior so as to leave any interval between them, and fix them with braces. When you are become expert, you will find, if the fly is not large, that a single brace will be sufficient for each pair of wings[1572]: but sometimes, if the card be not sufficiently stiff, you may confine it by a pin near the point. You must be careful in expanding the wings that each is brought equally forward. Lastly, give the antennæ their proper position, and if necessary confine them with braces; and leave your specimen in an airy situation to dry and stiffen. In a few days the braces may be removed, and the specimen transferred to the cabinet. When you put them away to become stiff, you must be careful to place them and your other insects at night where earwigs cannot come at them; for in sultry weather these animals will often then attack and spoil them.