Common objects of the microscope

by J. G. Wood

The forms of these organs are as varied as those of the insects to which they belong, and they are so well defined that a single antenna will, in almost every instance, enable a good entomologist to designate the genus to which the insect belonged. The functions of the antennæ are not satisfactorily ascertained. They are certainly often used as organs of speech, as may be seen when two ants meet each other, cross their antennæ, and then start off simultaneously to some task which is too much for a single ant. This pretty scene may be witnessed on any fine day in a wood, and a very animated series of conversations may readily be elicited by laying a stick across their paths, or putting a dead mouse or large insect in their way.

I once saw a very curious scene of this kind take place at an ant’s nest near Hastings. A great daddy long-legs had, unfortunately for itself, settled on the nest, and was immediately “pinned” by an ant or two at each leg, so effectually that all its struggles availed nothing. Help was, however, needed, and away ran four or five ants in different directions, intercepting every comrade they met, and by a touch of the antennæ sending them off in the proper direction. A large number of the wise insects soon crowded round the poor victim, whose fate was rapidly sealed. Every ant took its proper place, just like a gang of labourers under the orders of their foreman; and by dint of pushing and pulling, the long-legged insect was dragged to one of the entrances of the nest, and speedily disappeared.

Many of the ichneumon-flies may also be seen quivering their antennæ with eager zeal, and evidently using them as feelers, to ascertain the presence of the insect in which they intend to lay their eggs; and many other similar instances will be familiar to anyone who has been in the habit of watching insects and their ways.

It is, however, most likely that the antennæ serve other purposes than that which has just been mentioned, and many entomologists are of opinion that they serve as organs of hearing.

Fig. [15], Plate VI., represents a part of one of the joints belonging to the antennæ of the common house-fly; it is seen to be covered with a multitude of little depressions, some being small, and others very much larger. A section of the same antenna, but on a larger scale, is shown by Fig. [16], in order to exhibit the real form of these depressions. Nerves have been traced to these curious cavities, which evidently serve some very useful purpose, some authors thinking them to belong to the sense of smell, and others to that of hearing. Perhaps they may be the avenues of some sensation not possessed by the human race, and of which we are therefore ignorant. Fig. [17] represents a section of the antennæ of an ichneumon-fly, to show the structure of these organs of sense.

We will now glance cursorily at the forms of antennæ which are depicted in the Plate.

Fig. [1] is the antenna of the common cricket, which consists of a vast number of little joints, each a trifle smaller than the preceding one, the whole forming a long, thread-like organ. Fig. [2] is taken from the grasshopper, and shows that the joints are larger in the middle than at either end.

Figs. [3] and 5 are from two minute species of cocktailed beetles (Staphylínidæ), which swarm throughout the summer months, and even in the winter may be found in profusion under stones and moss. The insect from which Fig. [5] was taken is so small that it is almost invisible to the naked eye, and was captured on the wing by waving a sheet of gummed paper under the shade of a tree. These are the tiresome little insects that so often get into the eye in the summer, and cause such pain and inconvenience until they are removed.

Fig. [4] shows the antenna of the tortoise beetle (Cássida), so common on many leaves, and remarkable for its likeness to the reptile from which it derives its popular name. Fig. [3] is from one of the weevils, and shows the extremely long basal joint of the antennæ of these beetles, as well as the clubbed extremity. Fig. [7] is the beautifully notched antenna of the cardinal beetle (Pyrochróa), and Fig. [11] is the fan-like one of the common cockchafer. This specimen is taken from a male insect, and the reader will find his trouble repaid on mounting one of these antennæ as a permanent object.

Fig. [12] is an antenna from one of the common ground beetles (Cárabus) looking like a string of elongated pears, from the form of the joints. The reader will see that in beetles he is sure to find eleven joints in the antennæ.