Through a pocket lens

by Henry Scherren

The difficulty, however, may be easily got over, by reversing the position of the insect, and raising the head with a needle. The antennae will attract attention by their great length. In the male insect they exceed, while in the female they fall a little short of, the total length of the body. They are well worth examination. Even a low power will show that they consist of a number of joints—usually from seventy-five to ninety. The three basal joints are much larger than the rest, and in the female the third basal is nearly as long as the first. All these joints are thickly set with stiff hairs directed forwards. At the outer side of each antenna is a compound eye, and on the inner side is a pale spot, the fenestra, which in the males of some foreign Cockroaches is replaced by a simple eye.

If Cockroaches are kept in confinement, and forced out into the light, the constant motion of the antennae will satisfy the observer that they are of great use to their owners. By means of these organs they not only discover their food, but become by some means, probably by the motion of air-waves, aware of danger that threatens them. Belt, in his Naturalist in Nicaragua (p. 110), speaking of the Cockroaches that infest houses in the tropics, says, ‘They are very wary, as they have numerous enemies—birds, rats, scorpions, and spiders; their long, trembling antennae are ever stretched out, vibrating as if feeling the very texture of the air around them; and their long legs quickly take them out of danger.’ It is not given to every one to visit the tropics, but we may all use our eyes in observing the common insects that abound in our country, and in doing this we shall strengthen the habit of observation, and very often find confirmation of what we read of the habits of insects in distant lands.

Sir John Lubbock[18], in treating of the sense of smell in Insects, says that ‘Plateau put some food of which cockroaches are fond on a table, and surrounded it with a low circular wall of cardboard. He then put some cockroaches on the table: they evidently scented the food, and made straight for it. He then removed their antennae, after which, as long as they could not see the food, they failed to find it, even though they wandered about quite close to it.’

The large kidney-shaped compound eyes are sure to attract attention. It is worth while to take out and break up an eye, gently washing out the pigment. If we do this, and then examine it with the pocket lens, we shall have some idea of the multiplicity of lenses in the eye of a Cockroach, each of the six-sided facets being a lens.

Next come the mouth parts, which may be run over very quickly, for those of Beetles are formed upon the same plan, and from this primitive plan are derived the mouth parts of all other Insects, of whatever character they may be. To examine the mouth organs the insect must be turned on its back, and the labrum (a), or upper lip, raised with a needle, so as to allow of a general view of the rest. Then the jaws or mandibles (b) may be picked out with a needle. These jaws are strongly toothed, and work from side to side, and it is easy to see that they are very efficient organs. The lower jaws (c), or maxillae, lie below, and are compound organs, each being made up of several parts—the base, called the cardo or hinge (not shown in the illustration, but connected at right angles by a joint with the lower part, the stipes). From the stipes rise the galea, or helmet, on the outer side; and, on the inner side, the lacinia, to which the name maxilla is often applied, though it properly belongs to the whole. At the base of the galea is inserted the five-jointed maxillary palp, thickly set with hairs, and probably an organ of touch.

Fig. 33.—Mouth parts of a Cockroach.

By examining the maxillae (c) before they are separated, and comparing them with the labium (c) or under lip, which closes the mouth from below, it will be evident that there is no slight similarity between them. Nor is this strange: for the under lip consists of the second maxillae joined at their bases, which form the submentum (s) and mentum (m). (The former is the small, the latter the large white basal portion; the vertical line in the illustration shows the mental suture, and should be traced in the dead insect.) The organs in the centre constitute the ligula; and on each side of the labium is a three-jointed palp (labial), like that on the maxillae, thickly set with hairs, and with a similar function. It is well to work over the mouth parts a few times till the relation between the maxillae and the labium is seen and understood. The internal tongue (d) is attached to the inner side of the labium.

Now, still working on the under side of the insect, the three segments of the thorax are to be made out, and one cannot fail to notice the great size of the first joint (the coxa) in all the legs, and that these joints seem to serve as shields to protect the under side of the thorax. Then the different parts of the legs should be traced, and compared with Fig. 23 on p. 44. The spiny armature of the tibiae is to be noticed, as are the claws, between which is a projecting lobe, though this is absent in immature specimens. We shall find that the appendages of the thorax are the same as in the Margined Water Beetle. It is well to take as little as possible on trust, and to verify everything that we possibly can.

Now we may reverse the position of our subject, and having cut off the wing-cases, which are technically called teg´mina, examine the wings. These may be gently unfolded with a needle or a camel’s hair brush, when the longitudinal method of folding will be clearly seen, and the difference of the veining from that of the wings of the Margined Water Beetle will be apparent. A female should also be examined, and the small tegmina cut off, so as to see that not even the rudiments of wings are present.