118 THE CANADIAN ENTOMOLOGIST. 



the summer sun. Later, when the creek went down in the spring, 

 hundreds of larvje w^ere unable to follow the receding water and 

 perished of desiccation. Though we do not know the early larval 

 stages, the facts accounted indicate that its form and habits and 

 case must be very different from those of the mature larva. The 

 sluggish form that is known is incapable of locomotion, and the 

 case, with open bottom and tightly cemented periphery, is incapable 

 of transportation, even in following the few inches of fluctuation 

 of the creek. Yet some get to levels which during their early life 

 were exposed to the air; then perish because evident later modifica- 

 tions make them unable to follow the receding water. 



Not only do many larva; die on account of desiccation, but in 

 the spring quantities of larvae, as well as pupae, also perish from 

 some other cause. Until the latter part of April the larvae all 

 seemed healthy; then great numbers of them died and decomposed 

 in their cases. On the 1st of May 132 cases were examined. Of 

 these 15 contained living larvae, 9 cases were empty and lOS con- 

 tained Chironomid larvae. Apparently the Chironomids, the most 

 abundant insects in the stream, had found the cases already empty 

 or occupied only by the corpses of their previous occupants. It 

 seems probable that this high mortality was brought about by the 

 spring growth of algcE and deposits of silt smothering the Trichop- 

 tera to death, for larvae and pupae on the clean under surfaces of. 

 rocks, or in places free from deposits, lived to reach maturity. 



In the spring of 1914 there were very few /. confusa in the 

 stream — indeed, the entire Trichoptera population of all species 

 was far below its normal numbers. 



Larval Case. — The larval case, fig. 2, is from 5 — 6 mm. long 

 and 23/^ — 3 mm. wide. Its height above its support is barely 

 enough to accommodate its occupant. In breadth, howe\er, the 

 occupant is more thaii amply provided for, having an abundance 

 of room to turn around while completely within its case. At 

 each end of the case there is a circular opening not exceeding }/2 

 mm. in diameter. These openings sometimes are at the ends of 

 short tubular projections of the case. In structure the upper 

 surface of the case is composed entirely of closely woven silk 

 cemented tightly along the edges to its support. There is no floor 

 between the larva and the rock. 



