1 68 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



moss. The scorpion-flies have four, rather long, slender, mem- 

 branous wings with numerous veins, and long angular legs, 

 with which they scramble awkwardly about among green or 

 drying grass leaves. 



Order Trichoptera. The Trichoptera, or caddis-flies, com- 

 pose a small homogeneous order of four-winged insects many 

 of which look much like moths. In fact, there is little doubt 

 that this order may be looked on either as the direct ancestors 

 of the moths and butterflies or as a group descended from such 

 ancestors. The wings are membranous, but obscurely colored 

 by a covering of hairs and narrow scales; the antennae are long 

 and slender, and the legs delicate and unmodified. The in- 

 sects limit their flight to short, uncertain excursions along the 

 shore of the stream, and spend long hours in the close foliage 

 of the bank. So far as observed they take no food, although 

 they have fairly well-developed mouth-parts fitted, apparently, 

 for lapping up liquids. 



The eggs are dropped into water and the aquatic larvae 

 build protecting cases (hence the name, case- or caddis-flies) 

 of little pebbles, sand, or bits of wood fastened together by 

 silken threads. Some of the cases can be carried about by the 

 larva in its ramblings, but others are fastened to the boulders 

 or rock-beds of the stream. The larvae are caterpillar-like, 

 with head and thorax that project from the case, usually 

 brown and firm- walled, while the abdomen is soft and whitish. 

 They breathe by means of thread-like tracheal gills, and feed 

 on bits of vegetable matter and probably other small aquatic 

 creatures. Some have the interesting habit of spinning a tiny 

 silken net stretched in such a way that its broad shallow mouth 

 is directed up-stream so that the current may bring food into 

 it. When the caddis-worm is ready to pupate it withdraws 

 wholly into the case and closes the opening with a loose wall of 

 stones or chips and silk. When ready to issue the pupa usu- 

 ally comes out from the submerged case, crawls up to some 

 support above the water, and there the winged imago emerges. 

 Some kinds, however, emerge in the water. 



About 500 species of caddis-flies are known of which 150 



