Through a pocket lens

by Henry Scherren

This larva is a mud-dweller, and is best captured by scooping up surface mud near the banks of pools and ditches, just where the water shallows on to the shore. This should be washed in a small dish or saucer, so as to carry away the mud and leave the larvae wriggling on the bottom. They may be picked up with a brush and dropped into a bottle for transport home.

There is not the slightest difficulty about keeping them for observation. A bottle of the capacity of six or eight fluid ounces will make a good aquarium for a dozen or even twenty. The bottom should be covered to the depth of about an inch with mud fairly rich in organic matter. My own plan has been to use the accumulation from the bottom of a large aquarium. In this the larvae will bury the body, and feed, the tail protruding and thrust up to the surface of the water, of which there should be about two inches above the mud.

This is a liberal allowance of space. A couple of these larvae lived with me for some months in a glass capsule two inches in diameter and three-quarters of an inch in height. The mud at the bottom and the water covering it together measured about half an inch. Both pupated, and in due time from the pupa cases a perfect insect came out.

But that larvae may pupate, they require to be well fed. How shall we know when the bulk of the nourishment has been extracted from the mud? From the castings of the larvae; and these, though of a different shape, are as easy to be distinguished as the castings of the earthworm in the garden or those of the lobworm on the seashore. All the mud that passes through the bodies of the larvae is discharged in the form of tiny hard, cylindrical pellets; and when the mass consists of these pellets it should be changed, or the larvae will go short of food. They will, however, support long fasts.

From Fig. 88 we may get a good idea of the appearance of the larvae when kept in confinement. The figures are rather less than natural size, and all the attitudes were sketched from life. One is seen extended on the bottom; two are partially buried in the mud, with the breathing-tube protruding. The larva on the mud, and bent into curves, is just about to rise to the surface; others are shown in the act of rising, while one has its breathing-tube raised above the surface, and another is attached by the breathing-tube to the side of the glass vessel. The larva with the star-like process at the end of the tail is that of Odontomyia, a large bee-like fly.

Fig. 88.—Larvae of Ptychoptera paludosa (from life).

A larva of good size, like that of Ptychoptera, is especially easy to examine; and by reason of its transparency the tracheal tubes may be clearly traced. The under surface of the larva should be first looked at, and its adaptation for existence in the mud of a pond-bottom will be evident. The creature is legless, but possesses three pairs of false legs armed with dark-coloured hooks, and each body-segment bears a circle of stiff hairs, which enable the larva to travel through the mud, in the same way that the earthworm moves through the soil. Moreover, the segments between these circles are pretty thickly set with hairs.

The tracheal tubes run down on each side of the body, not in a direct line, for there is a most ingenious arrangement by which contraction and expansion of the larva, and the protrusion and retraction of the tail, are provided for. One can easily discern that in most of the segments the tubes are large, and that these large portions are connected by smaller tubes, whence others are given off into the body. These connecting-tubes are loop-like when the larva is of the normal length, but are straightened out, thus adding to their length, when the larva is extended.

The opening and closing of these loops may be observed at leisure if a larva be put in a long excavated slip, with some water, and then covered with a plain glass slip. The two slips, fastened together with small elastic bands, should then be laid on the stage of the dissecting microscope for examination; or they may be held in the hands, and the movements of the larva watched with the hand lens.