INSECTS 



165 



when the dehcate, gauzy-winged adult quickly issues. 

 The adult Mayfly (fig. 120) takes no food and lives only a 

 few hours, or at most a few days. It has the shortest 

 adult stage of all insects. The female drops her eggs 

 into the water. 



Firmly attached to stones, especially large ones, in 

 swift parts of the stream, may be found small cases, or 

 houses, composed of many small pebbles fastened together 

 with silk (fig. 121). In more quiet places in the stream, 



Fig. 121. — Two cases 

 or "houses" of cad- 

 dis-worms. (Natural 

 size; from speci- 

 mens.) 



Fig. 122. — Two cases of cad- 

 dis-worms, with the insects 

 showing head and thorax 

 projecting. (Natural size; 

 from specimens.) 



either attached to stones or resting on the bottom, or 

 sometimes floating in the water, may be found elongate 

 cases, an inch to two inches long, made of bits of wood 

 fastened together with silk, or of bits of pine-needles, or 

 even grass stems tied cleverly together by silken threads, 

 or it maybe tiny cornucopias composed of sand grains. All 

 these are the cases of the caddis-worms or case-worms, 

 and a caddis-worm itself may be found snugly con- 

 cealed in each case. Find cases with the head and fore 

 part of the worm projecting (fig. 122) and cases moving. 



