Directions for Collecting and Preserving Insects

by Charles V. Riley

The heat is derived from the flame of a spirit or petroleum lamp. Above this is placed a piece of sheet-tin, and over this the roasting proceeds. A bulging lamp cylinder, laid horizontally, serves as a roasting oven. In this the insect to be dried, when prepared as directed, and stuck on a piece of pith, is to be held over the flame; or the cylinder may be closed at the lower end with a cork, which should extend far inwards, and on this the insect should be fastened; the latter mode being preferable because the heat is more concentrated, and one hand is left free. The mode of procedure varies according to the nature of the objects to be treated. For the class of larger objects, such as Hemiptera, Cicadina, and Orthoptera, in their young stages of existence, the heat must not be slight, but a little practice shows the proper temperature required. If the heat be insufficient, a drying up instead of a natural distention ensues. The insect to be roasted is to be pierced by a piece of silver wire on the under side of the thorax, but it is not to be inserted so far as to damage the upper side, and the wire should then be carried through a disk of pith, placed beneath the insect, on which the legs should be set out in the desired position. But with some objects, such, for instance, as a young Strachia, the drying proceeds very quickly, so that if distention be not observed then the heat is too great, for the expansion of the air inside will force off the head with a loud report; also, with softer, thicker Pentatomidæ care must be taken to begin with a heat only so strong that the internal juices do not boil, for in such case the preparation would be spoiled. It is of advantage to remove the cylinder from time to time, and test, by means of a lens, if a contraction of the skin has taken place on any part; if so, the roasting is to be continued. The desired hardness may be tested with a bristle or wire.

For Aphides the living Aphis is to be put on a piece of white paper, and at the moment when it is in the desired position it is to be held over the flame, and in an instant it will be dead and will retain the attitude. Then put it, still on the paper, into the oven; or, still better, hold it over the heated tin, carefully watching the drying and moving the paper about in order to prevent it getting singed. The roasting is quickly accomplished in either way, but somewhat slower out of the oven especially in the larger kinds, such as Lachnus. If the paper turn brown it is a sure sign that caution is requisite. To pierce these brittle preparations for preservation is hazardous, and it is a better way to mount them with gum on card, placing some examples on their back.

For Cecidomyidæ, Agromyzidæ, Cynipidæ, and other small insects liable to shrink, yet containing but little moisture, such as Poduridæ, Pediculidæ, Psyllidæ, etc., another method is adopted. Over the insect, mounted on a wire, etc., as above directed, a thin chemical reagent glass or glass rod, heated strongly at one end, is held, and the heat involved is generally sufficient to bring about the immediate drying and distention, but if the heat be too little the process must be repeated; and, although by this method the danger of burning is not obviated, yet the position of the legs is maintained much better than by the aforesaid roasting.

Larvæ of all kinds, up to the size of that of Astynomus ædilis, even when they have long been kept in spirits, may be treated successfully by the roasting method; but with these objects care must be taken that the heat is not too strong or else the form will be distorted. For small larvæ it is preferable to use a short glass, in order better to effect their removal without touching the upper part, which becomes covered with steam, and contact with which would cause the destruction of the preparation. Larvæ of Coleoptera, which contain much moisture or have a mucous surface, must lie on a bed of paper or pith in order to prevent adhesion and burning, and these may be further avoided if the cylinder be slightly shaken during the process, and the position of the object be thereby changed.

Many Aphides and Coccids are covered with a waxy secretion which interferes very materially with their easy examination. Mr. Howard has overcome this difficulty by the following treatment:

“With Aphides and Coccids which are covered with an abundant waxy secretion which can not be readily brushed away, we have adopted the plan of melting the wax. We place the insect on a bit of platinum foil and pass it once over the flame of the alcohol lamp. The wax melts at a surprisingly low temperature and leaves the insect perfectly clean for study. This method is particularly of use in the removal of the waxy cocoon of the pupæ of male Coccidæ, and is quicker and more thorough than the use of any of the chemical wax solvents which we have tried.” (Insect Life, I, p. 152.)

[Mounting Specimens for the Microscope.]—The study of the minuter forms of insect life, including Parasites, Thysanura, Mallophaga, the newly hatched of most insects, etc., requires the use of the microscope, and some little knowledge of the essentials of preparing and mounting specimens is needed. The subject of mounting the different organs of insects and the preparation for histological study of the soft parts of insects opens up the immense field of microscopy, the use of the innumerable mounting media, the special treatment of the objects to be mounted, staining, section-cutting, and many other like topics, a full description of which is altogether out of place in the present work. Anyone desiring to become thoroughly versed in the subject should consult some of the larger manuals for the microscopist, of which there are many. For the practical working entomologist, however, a knowledge of all these methods and processes is not essential, and in my long experience I have found that mounting in Canada balsam will answer for almost every purpose. The softer-bodied forms will shrink more or less in this substance, and it is frequently necessary to make studies or drawings of them when freshly mounted; or, if additional specimens are preserved in alcohol, they will supplement the mounted specimens and the material may be worked up at the convenience of the student. The materials for the balsam mounts may be obtained of any dealer in microscopical supplies. They consist of glass slides, 3 inches by 1 inch, thin cover-glasses of different dimensions, and the prepared balsam. The balsam is put up very conveniently for use in tin tubes. A sufficient quantity is pressed out on the center of the glass slide, which has previously been made thoroughly clean and dry, the insect is removed from the alcohol, and when the excess of liquor has been removed with bibulous paper, it is placed in the balsam, the limbs and antennæ being arranged as desired by the use of fine mounting-needles. A cover-glass, also made thoroughly clean and dry, is then placed over the specimen and pressed gently until the balsam entirely fills the space between the cover and the glass slide. The slide should then be properly labeled with a number referring to the notes on the insect, preferably placed on the upper edge of the slide above the cover-glass, and also a label giving the number of the slide and the number of the slide box. On the opposite end of the slide may be placed the label giving the name of the specimen mounted and the date. If a revolving slide table is employed to center the mounts, the appearance of the slide may be improved by adding a circle of asphalt or Brunswick black. With the balsam mounts, however, this sealing is not necessary. The slide ([Fig. 110]) should then be placed in a slide case with the mount uppermost, and should be kept in a horizontal position to prevent sliding of the cover-glass and specimen until the balsam is thoroughly dried. For storing slides I have found very convenient the box shown at [Fig. 111]. It is constructed of strong pasteboard and is arranged for holding twenty-six slides. The cover bears numbers from 1 to 26, opposite which the name of each insect mounted, or the label on the slide, may be written. This box when not in use is kept in a pasteboard case, on which may be placed the number of the box. These slide cases may be stored in drawers or on shelves made for the purpose. In mounting specimens taken from alcohol it is advisable to put a drop of oil of cloves upon them, which unites with the balsam and ultimately evaporates. The occurrence of minute air bubbles under the cover-glass need occasion no uneasiness, for these will disappear on the drying of the balsam.

Fig. 110.—Balsam mount, showing method of labeling, etc. (original).

In mounting minute Acarids or mites it has been found best to kill the insects in hot water, which causes them to expand their legs, so that when mounted these appendages can readily be studied. If mounted living, the legs are almost invariably curled up under the body and can not be seen. This method may also be used in the case of other minute insects. Some insects, such as minute Diptera, are injured by the use of hot water, and for these dipping in hot spirits is recommended.