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.

Microscopists who care to follow up the study of insects’ mouths will know that they are accumulating really useful knowledge. Those who do not desire to go so deeply into the matter may well spare a few moments for the examination of the green fly mouth, a needle-like piercing organ which is thrust into plants for the purpose of sucking their sap. The mouth of the gnat is a more difficult subject for the microscopist, though no less interesting; it may be compared with the same organ of the green fly, for it is used somewhat similarly, with the difference that it sucks blood and not plant juices. It may be well to mention here that the females alone suck blood, but it is easy to distinguish the sexes, for the antennÆ or feelers of the females are thread-like whilst those of the males are feathered. A few adult insects have no mouths, for they never feed during their short lives.

Caterpillars of all kinds and also beetles, grasshoppers, cockroaches and the like have biting-mouth parts, and the student, who is not well versed in insect anatomy, will learn more by watching one of these insects partaking of a meal than by trying to discover the uses of the various parts with the aid of a microscope. Caterpillars as a rule are not shy feeders, and a pocket lens will show their sickle-like jaws in full play. The grubs of house-flies are worth examining; they are soft and fleshy except for a pair of horny hooks which are used to tear up the food material. There are, however, so many different mouths we cannot describe even the typical ones, but the microscopist will soon discover those of special interest.

The feet of insects do not show so much variation as their mouths, nevertheless they will afford ample material for many hours of study. Our butterfly, which is now but a remnant, will provide our first object. The design of its feet will depend, to some extent, on the species of insect, but they will certainly be clawed. Other insects with clawed feet—beetles, bees, and wasps—may be examined, and we shall see that there are minor differences amongst them though their general plan is similar. Sometimes we find a simple pair of claws on each foot, in other cases each claw has a little spur, whilst spiders, which, by the way, are not insects, have comb-like claws. The foot of the house-fly is not only provided with a pair of claws, but also with a soft fleshy pad, by means of which it is enabled to climb window panes and similar smooth surfaces. If we are fortunate enough to obtain a specimen of a louse, human or otherwise, we must not fail to notice its strong grasping claw, used for taking a firm hold of the hair of the creature on which it lives. Such objects are better examined under a high magnification, along with a hair, then the actual method of grasping may be observed.

The feelers of some insects are interesting; those of gnats we have already mentioned, but they may be examined in detail. Those of beetles are of very diverse form; some are thread-like, some clubbed, some fan-shaped. Moths, too, have many curious designs to show. Some of these feelers, when highly magnified, may be seen to be pitted—hundreds of little sunken areas are scattered over their surfaces, and it is probable that they are connected with a sense of smell. In that case the feeler is a more important organ than one might surmise from its popular name.

The hairy clothing of insects need not delay us long. Most interesting of all are the feathered hairs of certain bees. In our chapter on botanical work with the microscope we mentioned the feathery stigmas of grass flowers and we also stated that they took that form, so that pollen grains blown to them would be entangled in their branches. The hairs of many bees are feathered for a similar reason, they gather pollen and the pollen adheres to these “feathers” much more readily and in much greater quantity, than it would to simple, unbranched hairs. Some bees collect no pollen and, from them, feathered hairs are wanting.

Any microscopist who has followed us thus far, will have a fair idea of the structure of a number of insects. In every case, where possible, comparisons should be made between similar organs of different insects and the investigations may be made more interesting by observing the habits of the insects and trying to discover reasons for the differences in structure. It is safe to surmise that there is a reason in every case. There are many other interesting subjects which we have not mentioned, the legs of insects—running legs of ground beetles, digging legs of mole crickets, swimming legs of water beetles and the wonderful pollen-carrying legs of bees. Then again, the eggs of many insects are of surpassing beauty in shape, they may be round, oval, oblong, nearly square and almost needle shaped; some are smooth and shining like burnished metal, others beautifully sculptured; some resemble miniature birds’ eggs, others are not unlike the seeds of plants.

Many insects are too small to be cut up into their various parts, legs, feet, wings, etc., by unskilled hands and they must be examined whole. Perhaps you may think that an insect will be too big an object for your microscope. Indeed there are some insects which measure nearly a foot in length, but there are, on the other hand, beetles no longer than one hundredth part of an inch. When we examined the house-fly it is not unlikely that we found some minute creatures living upon it. None of these is likely to be an insect, but as they are closely related we may mention them here. Beneath the wings of the house fly there are often minute, red, six legged young mites, all eagerly sucking the juices of their host. Because they are six legged we may be led to think that they are insects, for the entomologist knows that the true insect, in its adult form, never has more than six legs. These mites, however, later in life, drop from the fly and by developing another pair of legs appear in their true colours. Various other mites, including cheesemites, may be found clinging to the house-fly, in fact it is by the aid of these insects that cheesemites are often carried from cheese to cheese. One of the most curious parasites of the house-fly must be sought upon its legs. If the search is successful, curious, reddish-brown creatures, armed with formidable pincers, and strangely reminiscent of miniature lobsters, will be found clinging thereto. They are called chelifers and their home is the manure heap, so that their presence shows us only too well where our friend the fly has recently disported himself. His next visit was probably to our food.

If we can find a swiftly running stream within easy reach a little time may be spent in searching the submerged rocks and plants for the miniature stages of the buffalo gnat. This insect, which is known to scientists as Simulium, has a most interesting life history. Its popular name is derived from its hump-backed appearance and its supposed resemblance to a buffalo. The female lays her eggs on a rock or reed, just covered by running water, she never lays them in still water. The greenish-brown, club-shaped grubs which come from the eggs are curious and they will repay examination under a low magnification. At the more blunt end of the creature there is a large sucker; it uses this as a foot to support itself in an upright position. If we examine our specimen under water we shall see that its horny head is decorated with a pair of fans, each one composed of about fifty threads. These fans open and close with a rhythmic movement and, in doing so, attract small floating water plants to the mouth. Just below the head there is a single leg with a sucker foot. When the grub walks, it does so by a looping movement, holding fast to its support with fore and hind suckers alternately.

The next stage in the life of the young buffalo gnat is even more curious. On the surface of some submerged leaf we shall probably be able to find a number of the slipper-shaped pockets made of closely woven silk, in which the insect spends the final portion of its life before turning into the perfect fly. Within some of the pockets we shall find the creature itself and it must be studied. Its head is still ornamented with a pair of fans, but in this case they are gills by means of which the insect breathes and not food scoops, for it has reached a stage when food is not taken. On its tail end there is a hook, by means of which it anchors itself to its slipper-shaped pocket. Probably we shall find bubbles of air collecting round some of the insects, within their pockets; as the time approaches nearer and nearer for the change to the perfect insect to take place the bubbles grow larger and larger. Eventually the fly emerges within a bubble, shakes it free from the pocket and floats to the surface of the water without wetting its wings.

The pond will supply insects quite as interesting as the running stream. Here we may find the eggs of Caddis flies, enclosed in jelly-like envelopes, rope-like, horse-shoe shaped or simple masses. The caterpillar cases of these insects should be slightly magnified and examined, for they are marvellously constructed of shells or sand, pieces of stick, leaves or other vegetation.

We may come across the young stages of the common gnat. Its eggs are very small and when the mother gnat lays them on the surface of ponds she glues them together so that they form what is known as an “egg raft.” The “raft” we shall notice, if we examine it carefully, is composed of a large number of eggs; each egg is elongated, pointed at one end and blunt at the other. Every egg is arranged with its blunt end downwards for, from that end, the larvÆ gnats make their way into the water. A larva, it may be explained, is the stage in insect development which follows the egg; the next stage is known as the pupa. When the eggs are first laid they are white but, before they hatch, they become darker and darker, till they are almost black. The larvÆ which hatch from the eggs we must examine under our microscope and also in the water—they may easily be kept in a small jar of pond water. If we study their habits carefully, we shall observe that they float almost at right angles to the surface of the water and that, while doing so, the tip of a little peg-like outgrowth on the tail end of their bodies is thrust out of the water. The little peg is the breathing organ of the gnat larva and the flaps which open and close at its tip are worth examination. In a few days, the denizens of our pond water will change their appearance and become comma shaped. On their heads we shall see a pair of curious horns, which project out of the water as the creatures, which have now become pupÆ, float at the surface. The horns are breathing organs. As we examine these pupÆ, day by day, we shall see the various parts of the complete gnat as they develop within the body of the comma. Finally, under the microscope, we can trace all the parts of the gnat. Darker and darker the little creatures become, as development proceeds; at the same time they become less active and less comma shaped. At length the time comes when they straighten their tails somewhat violently, their skin splits along the back and out comes the perfect gnat. We can use him for further microscopic work, so we will not let him go. If he be a male, his beautiful feathered feelers or, if a female, her thread-like feelers will make good objects for us, the scales from head and body, the wings and feet are all worth the time we may spend in examining them. The mouth parts, too, are interesting but rather complicated.

Many insects are capable of emitting more or less musical sounds. In some countries these so-called singing insects are kept as pets, in other countries the same insects are voted a nuisance; it is all a matter of taste. Of all musical insects, the most noted is the Cicada and its sound organs are easily seen; they occur only in the male, for the female never sings. The Cicada belongs to the same great order of insects as the green fly, which we have already mentioned. There is one British species, and our readers who visit the New Forest may come upon it. On the under side of one of these insects the beak, very similar to the beak of the green fly, may be plainly seen. On either side of the insect, just below the bases of the wings there are two nearly round discs. These discs cover the sound organs, which are two ear shaped membranes. By means of muscles the insect can cause the membranes to vibrate and thus produce the sound which once heard, can never be forgotten.

More easily found insects, in this country, at any rate, are the cricket and the grasshopper. The cricket we all know is a persistent songster. Let us examine him closely. We shall find, that the house cricket has two pairs of wings; the fore wings are leathery, the hind wings membranous. If we watch a male in the act of chirping, the male crickets like the male Cicadas are the songsters, we shall observe that he moves his wings slightly. If now we examine a dead male, we shall find, on the under surface of the forewing, a rough patch. Let us examine this patch under the microscope, it reminds us of nothing so much as a file: it is a file in fact, and sound is produced by rubbing this rough file against a ridge, which we can easily see, on the upper surface of the hind wing.

It would be a useless accomplishment for the cricket to be able to sing, if there were no ears to hear its song. Nature has arranged that his song shall not go unheard and if we examine a female cricket, that is to say a cricket which has no sound-producing apparatus, we shall find an oval depression, covered by a membrane, on each of her front legs; these are her ears and they enable her to hear her mate calling to her.

We have often heard the song of the grasshopper as we have walked through the fields and he too will occupy our time for a few moments. When he sings, he kicks his legs rather violently and this gives us a clue to the situation of his vocal organs. The inside of each of his hind thighs is ridged and the edge of each ridge is, as we can see if we magnify it, rough like a file. This file-like ridge is rubbed against a smooth ridge on the edge of the fore wing and the result is the familiar note of the grasshopper.

This insect also has ears, but they are not easy to find unless they are pointed out to us. If we examine a grasshopper we shall see that its body is divided into three parts: a head, a solid portion from which the wings and legs arise, the thorax and a portion (the abdomen) made up of a number of rings or segments. On the sides of the first of these rings, counting from the forward end, we shall find small depressions covered with membrane, these are the ears. It is curious that although many of the grasshoppers cannot give out a note, so far as human ears can detect, they nearly all have ears; maybe there is a grasshopper song which only grasshoppers can hear.

Very many other insects have sound organs, but they are nearly all constructed on the same plan. It may seem surprising that sounds can be produced by these simple means. Sound is really caused by waves in the air and these insect vocal organs set up rapid sound waves, by their vibration.

The microscopist should never be at a loss for objects derived from the insect world: it is impossible to walk without treading upon some six legged wayfarer. The wing cases of beetles are often of rare beauty, some on account of their sculpturing, some because of a mantle of scales.

In our greenhouse and garden we can find mealy bugs, curious little powdered insects which do an enormous amount of damage. The fringe wings, or Thrips, are common and destructive; examine their curious feet and their beautifully fringed wings, the sight will repay you. And lastly, if you number an insect enthusiast amongst your friends, enlist his aid in gathering objects for your microscope.