Directions for Collecting and Preserving Insects

by Charles V. Riley

[Inflation of the Larvæ of Lepidoptera.]—The larvæ of Lepidoptera preserved in alcohol are excellent for anatomical and general study, but are not very suitable for use in economic displays. This means of preservation also has the disadvantage of not generally preserving the natural color and appearance of the specimens. These objections may be avoided, however, by the dry method of preserving larvæ, viz, by blowing or inflation. The process may be described as follows: The larva may be operated upon alive, but should preferably be first killed by dipping in chloroform or alcohol, or in the cyanide bottle. It is then placed on a piece of blotting paper and the alimentary canal caused to protrude from one-eighth to one-fourth of an inch, by rolling a pencil over the larva from the head to the posterior extremity. The protruding tip is then severed with a sharp knife or pair of dissecting scissors, and the contents of the abdomen are forced out by passing a pencil, as before, a number of times over the larva. Great care should be exercised in expressing the fluids not to press the pencil too strongly against the larva or to continue the operation too long, as this will, especially in delicate larvæ, remove the pigment from the skin, and the specimen when dried will show discolored spots and be more or less distorted. The larva should be moved from place to place on the blotting paper during the operation, so as not to become soiled by its own juices. A straw, or a glass tube drawn to a point at the tip, is then inserted in the protruding portion of the alimentary canal. If a straw is used the larva may be fastened to it by thrusting a pin through the wall of the canal and the straw. In the case of the glass tube the alimentary canal can be caused to adhere by drying for a few minutes and this operation may be hastened and the fastening made more secure by touching the point of union with a drop of glue. The straw or glass tube is then attached to a small rubber bag, previously inflated with air, the ordinary dentist's or chemist's gas bag answering admirably for this purpose. The larva is now ready for drying, and for this purpose a drying oven is required into which it is thrust and manipulated by turning it from side to side, to keep it in proper shape and dry it uniformly until the moisture has been thoroughly expelled. An apparatus which I have found very convenient for this purpose is represented at [Fig. 109]. It consists of a tin box with mica or glass slides, e, to allow the larva to be constantly in sight. It has also a hinged top, b, which may be kept closed or partly open, or entirely open, as may be necessary, during the operation. The ends of the box are prolonged downward about 5 inches, forming supports for it, g. Beneath it is placed an alcohol lamp, f, which furnishes the heat. In the end of the box is a circular opening, d, for the introduction of the larva, and this may be entirely or partly closed by a sliding door, a. It will be found of advantage to line the bottom of the box (inside) with a brass screen of very fine mesh to distribute and equalize the heat. This apparatus can be very easily made by any tinsmith and will answer every purpose.

Fig. 109.—Drying oven for the inflation of larvæ (original).

The larvæ of Microlepidoptera or young larvæ may be dried without expressing the body contents, and will keep, to a great extent, their normal shape and appearance. The method consists in placing them on a sand bath, heated by an alcohol lamp. The vapor generated by the heat in the larvæ inflates them and keeps the skin taut until the juices are entirely evaporated. They may then be glued at once to cardboard and pinned in the cases.

In the mounting of large inflated larvæ I have adopted the plan of supporting them on covered copper wire of a size varying with the size of the larva. A pin is first thrust through a square bit of cork and the wire brought tightly about it and wrapped once or twice, compressing the cork and giving a firm attachment to the pin. The wire is then neatly bent to form a diamond-shaped loop about one-sixth of an inch in length and again twisted loosely to the end—the length of the twisted portion about equalling that of the larva to be mounted. This is then either thrust into the blown skin of the larva through the anal opening, the larva being glued to the wire by the posterior extremity, or the larva is glued to the wire by the abdominal legs and venter, thus resting on the wire as on a twig. This style of mounting is illustrated in Pl. I. With a little experience the operator will soon be able to inflate the most delicate larvæ and also the very hairy forms, as for instance Orgyia leucostigma, without the least injury, so that the natural colors and appearance will be preserved.

Another very good method, and still safer, is to blow with straw, cut the straw square off at the anus, and then preserve the thoroughly dried and blown specimen in a glass tube of about the same length and diameter as the larva. This arrangement in conjunction with the tube holder, which will be described further on, is one of the most satisfactory for the preservation of inflated larvæ.

For the biological-display collection, larvæ may be blown in various natural positions, to be subsequently fastened on leaf or twig or in burrows which they have occupied. Fastened to artificial foliage in which nature is imitated as much as possible, such blown larvæ are quite effective.

[Stuffing Insects.]—Large larvæ may sometimes be satisfactorily preserved for exhibition purposes by stuffing them with cotton. The method consists simply in making a small slit with the dissecting scissors or a short scalpel between the abdominal prolegs, and removing the body contents. Powdered arsenic or some other preservative should be put in the body of the larva with the cotton used in stuffing it, and the slit closed by a few stitches, when the larva may be dried and mounted on a twig or leaf. This method of stuffing with cotton is also applicable in the case of certain large-bodied insects which, if mounted and put away without preparation, would be liable to decompose, as, for instance, the larger moths, grasshoppers, etc. A slit can be made in the center of the abdomen or near the anus beneath, and the body contents removed and replaced with cotton. Stuffing in this way with cotton is of especial advantage in the case of certain of the large endophytous insects which grease badly. The cut will not be noticed after the insect has dried, or it may be closed by a stitch or two.

[Dry Preservation of Aphides and other soft-bodied Insects.]—Difficulty has always been experienced in preserving soft-bodied insects, particularly Aphides, in a condition serviceable for subsequent scientific study. Kept in alcohol or other antiseptic fluid, they almost invariably lose much of their normal appearance, and many of the important characteristics, especially of color, are obscured or lost. The balsam mount is also unsatisfactory in many respects, as the body is always more or less distorted and little can be relied upon except the venation and the jointed appendages. A method of preserving soft-bodied insects by means of the sudden application of intense heat was communicated to the Entomologische Nachrichten, Vol. iv, page 155, by Herr D. H. R. von Schlechtendal. It is claimed for this method that the Aphides and other soft-bodied insects can be satisfactorily preserved in form and coloring, the success of the method being vouched for by a number of well-known German entomologists, Kaltenbach, Giebel, Taschenberg, Mayr, and Rudow. A condensed translation of the method employed by Schlechtendal is given by J. W. Douglas in the Entomologists' Monthly Magazine for December, 1878, which I quote: