1911 Encyclopædia Britannica/Caddis-Fly and Caddis-Worm

CADDIS-FLY and CADDIS-WORM, the name given to insects with a superficial resemblance to moths, sometimes referred to the Neuroptera, sometimes to a special order, the Trichoptera, in allusion to the hairy clothing of the body and wings. Apart from this feature the Trichoptera also differ from the typical Neuroptera in the relatively simple, mostly longitudinal neuration of the wings, the absence or obsolescence of the mandibles and the semi-haustellate nature of the rest of the mouth-parts. Although caddis-flies are sometimes referred to several families, the differences between the groups are of no great importance. Hence the insects may more conveniently be regarded as constituting the single family Phryganeidae. The larvae known as caddis-worms are aquatic. The mature females lay their eggs in the water, and the newly-hatched larvae provide themselves with cases made of various particles such as grains of sand, pieces of wood or leaves stuck together with silk secreted from the salivary glands of the insect. These cases differ greatly in structure and shape. Those of Phyrganea consist of bits of twigs or leaves cut to a suitable length and laid side by side in a long spirally-coiled band, forming the wall of a subcylindrical cavity. The cavity of the tube of Helicopsyche, composed of grains of sand, is itself spirally coiled, so that the case exactly resembles a small snail-shell in shape. One species of Limnophilus uses small but entire leaves; another, the shells of the pond-snail Planorbis; another, pieces of stick arranged transversely with reference to the long axis of the tube. To admit of the free inflow and outflow of currents of water necessary for respiration, which is effected by means of filamentous abdominal tracheal gills, the two ends of the tube are open. Sometimes the cases are fixed, but more often portable. In the latter case the larva crawls about the bottom of the water or up the stems of plants, with its thickly-chitinized head and legs protruding from the larger orifice, while it maintains a secure hold of the silk lining of the tube by means of a pair of strong hooks at the posterior end of its soft defenceless abdomen. Their food appears for the most part to be of a vegetable nature. Some species, however, are alleged to be carnivorous, and a North American form of the genus Hydropsyche is said to spin around the mouth of its burrow a silken net for the capture of small animal organisms living in the water. Before passing into the pupal stage, the larva partially closes the orifice of the tube with silk or pieces of stone loosely spun together and pervious to water. Through this temporary protection the active pupa, which closely resembles the mature insect, subsequently bites a way by means of its strong mandibles, and rising to the surface of the water casts the pupal integument and becomes sexually adult.

The above sketch may be regarded as descriptive of the life-history of a great majority of species of caddis-flies. It is only necessary here to mention one anomalous form, Enoicyla pusilla, in which the mature female is wingless and the larva is terrestrial, living in moss or decayed leaves.

Caddis-flies are universally distributed. Geologically they are known to date back to the Oligocene period, and wings believed to be referable to them have been found in Liassic and Jurassic beds.  (R. I. P.)