CHAPTER XIV
THE MICROSCOPE AND INSECT LIFE
Some of our readers will probably remark that entomology, or the natural history of insects, is really a branch of zoology and should be treated as such. We cannot pretend that they are wrong, but it is such a specialized branch that it merits separate treatment. Not many years ago insects, with few exceptions, were looked upon as harmless and often beautiful dwellers upon the earth. They afforded endless amusement to certain enthusiasts who collected them for their colouring or their odd forms. Recent developments of our scientific knowledge have shown us that the insect is, other human beings excepted, man’s most serious rival for the mastery of the world.
This state of affairs has been beautifully depicted by an American naturalist; his words described a by no means unlikely final scene on this earth of ours. He wrote: “When the moon shall have faded from the sky and the sun shall shine at noonday, a dull cherry red, and the seas shall be frozen over, and the ice-cap shall have crept downward to the Equator from either pole, and no keel shall cut the waters, nor wheels turn in mills, when all cities shall have long been dead and crumbled into dust and all life shall be on the very last verge of extinction on this globe, then, on a bit of lichen, growing on the bald rocks beside the eternal snows of Panama, shall be seated a tiny insect, preening its antennæ in the glow of the worn-out sun, representing the sole survival of animal life on this our earth—a melancholy ‘bug.’”
There is probably no field more interesting for the microscopist than that provided by the insect world. Unlimited explorations may be made with the certainty of finding something new at every turn. Most people begin their studies of insect life with butterflies and moths; some folk to their loss never proceed further. We may well follow the usual course, and make a butterfly our first study.
Any butterfly or moth will do for our purpose, any one with coloured wings, for some have clear wings like those of the bees and wasps, but they are not very common, so that we shall probably find a suitable specimen at the first attempt. The more highly coloured the specimen, the more attractive it will appear under the microscope. After killing the insect, and not before, we may proceed to study it. Killing may best be accomplished by means of a killing bottle, failing this a hard nip on the body, between thumb and finger, will do, but it must be no half-hearted proceeding or the insect will be injured without being killed.
Having removed a wing and placed it on the stage of our microscope, we must examine it by reflected light, for it is not transparent. This may be accomplished, if we are using artificial light, by raising the source of illumination well above the object, so that the light strikes it at an angle of about forty-five degrees; by daylight reflected light is easily managed. If we have never previously examined a similar object we will be surprised at its appearance. All the beautiful reds and blues, yellows and greens which comprise the brilliant livery of these insects are seen, under the microscope, as hundreds of minute scales which overlap one another like tiles on a roof. A higher magnification will show that each scale is roughly flask-shaped, and that its narrow end fits into a little socket in the wing proper. When the scales are rubbed from the wing, nothing remains but a transparent substance traversed by veins—to the microscopist the scaleless wing is of little interest; to the entomologist it is important, for the moths, at anyrate, are arranged into families largely according to the arrangement of the veins of their wings.
Many other wings may be examined with advantage; gnats, for example, are clothed with scales of varied shape, some hair-like, some forked, some resembling a sickle, and some disc-shaped; these forms, by the way, do not all occur upon the wings, but are found upon the head and other parts of the body as well. The wonderful gauzy, iridescent wings of dragon flies are interesting; those of various flies worth examination also those of bees on account of the clever device for uniting the front and hind wings during flight. On the front edge of the hind wings the microscope will show us a row of minute hooks. When the bee makes a flight, it hooks its hind wings to a ridge on the hinder edge of the fore wings, so that for flying purposes it has, to all intents, two wings instead of four.
Having examined all the wings we can find for the time being, we may turn our attention to mouths. The mouth parts of insects are not only interesting but important; one of the first things an economic entomologist does with a new specimen is to examine its mouth parts. The mouth will tell us what manner of feeder its owner may be. Some insects have sucking mouths, and they must feed perforce on liquids; others have biting mouths, and they are likely to do damage to crops by eating them. Then there are lancet-like mouths and mouths which are a compromise between biting and sucking ones. The subject, however, is somewhat complicated, and entails a knowledge of insect anatomy, so we will merely deal with a few easily understood examples. Our butterfly has a sucking mouth; it is known as a proboscis, and may be found, coiled like a watch spring, beneath its head. There is no trace of anything in this mouth capable of biting or even piercing the most delicate structure. The house-fly is also possessed of a proboscis though of different design. Though a dangerous, disease-carrying insect, it can do no harm with its mouth. The partiality of the house-fly for sugar is well known, and it is interesting to learn how, with its soft fleshy mouth, it can satisfy its cravings. Let us watch one at work on a lump of sugar through our pocket lens. If we look carefully we shall notice that the fly, as he thrusts his proboscis here and there, emits from it a little drop of liquid; after a momentary pause the liquid is sucked up again, it has dissolved a little of the sugar, and the fly enjoys the sugar-laden liquid.
People frequently state that they have been bitten by a house-fly—a sheer impossibility. What really happens is that they mistake the very similar stable fly for the house-fly. If one of these insects be captured and examined, we shall find not the soft fleshy proboscis of the house-fly, but a cruel looking, awl-like mouth easily able to penetrate the human skin. Certain tropical flies, known as Pangonias, have such formidable and lengthy piercing mouths that they can penetrate thick clothing and puncture the skin below.