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.
1. The Head of a Beetle
A remarkable beetle, with enormously developed fore-legs. The object of these long legs is not known.