Home › Volumes › Insects › Caddis Flies

Family Hydropsychidae

The caddis flies which should possess the greatest interest for us, because it is a personal interest, belong to this group. Their larvae are the only caddis worms which are carnivorous. They are found both in streams and in ponds, but more commonly in streams. They are elongate and slender, with short legs, and with anal projections which bear strong curved claws with which they hold to the surface of rocks or to their cases. Their cases are fixed and are generally composed of bits of stone fastened to large stones or rocks at the bottom of the water. Sometimes several larvae appear to live in company in a common case, being covered by a sheet of silk, to which minute fragments of leaves and sticks are fastened. There is usually more silk in the construction of the cases of these insects than with the caddis worms of the other families which have stony cases, and although the stones attached to it may be few in number, there is apt to be a pretty dense, silken tube. Sometimes this tube is simply covered with slimy mud and has no other foreign objects attached to it. Some of these larvae prey upon other aquatic insects and it is probable that this is a general habit of the group.

An interesting form which I have watched in Rock Creek, near Washington, inhabits a case shaped like a funnel, the tube of the funnel bent nearly at right angles with the mouth. The mouth is composed of a network of silk supported by arched bits of twigs. The larva remains hidden in the funnel, watching for its prey to be caught in the open mouth. The cases were preferably placed at the edge of slight depressions in the rocky surface so that the tubular portion was protected from the full force of the current. On the surface of a rock about eighteen inches in diameter 166 of these nets were counted. The larvae of one of the black flies were very abundant in this stream and were washed into the mouths of these nets and probably formed the principal food of the Hydropsyche larvae. Therefore, this is one of the few creatures which we know which helps to reduce the number of black flies and it must therefore be considered as very beneficial to mankind. The family is a rather large one and nearly thirty species are known to occur in this country, about half of them belonging to the typical genus Hydropsyche. Macronema zebratum Hagen is one of our handsomest species. Its wings are beautifully spotted and banded with yellowish brown. It occurs from Canada south to Virginia.