Pupat i on 



Preparation or alteration of the case. At the end of the 

 last stage, the larva begins to prepare itself for pupation. Its behavior 

 changes; it ceases to feed, crawls to a concealed place for pupation and 

 begins to build the pupal case. Larvae living in portable cases usually 

 94 attach their case to a fixed object and adapt it to the pupal stage; species of 

 Annulipalpia with a free larva begin to build, before pupation, structures with 

 an external layer consisting of material from their environment. 



The larvae of Rhyacophila build a rooflike pupal case of small stones 

 (Figure 141, A), attaching its base to the stone by dense strands of silk with 

 numerous ventilation holes. The stones are solidly connected by similar 

 ribbonlike strands; they are rarely fully contiguous; the larva does not 

 build a continuous inner wall of the case but leaves spaces free of the silk 

 (Figure 141, B); thus, although the pupal case of Rhyacophila is very 

 strong, it is also open to circulation of the water. 



After completion of the case, the larva of Rhyacophila begins to 

 weave the cocoon which is characteristic for all Annulipalpia; however, 

 unlike the cocoon of the other families of the suborder, the cocoon of 

 Rhyacophilidae and Glossosomatidae is very thick and strong. 



The larva of Rhyacophila begins weaving the cocoon by drawing 

 longitudinal threads from one end of the cave to the other, so that the larva 

 is situated inside the threads; the larva then interweaves the longitudinal 

 threads with transverse and oblique threads (Figure 142); it fills the small 

 open spaces with silk, so that a thick continuous elastic wall is formed. 

 The pressure inside the cocoon is greater than the pressure in the environ- 

 ment so that the cocoon becomes inflated and its walls become shining and 

 smooth; when the wall is pricked with a needle, it collapses and the fluid 

 flows out. The dorsal surface of the cocoon is convex and the ventral 

 surface is slightly concave in the middle so that the cocoon has an oblong 

 form like a bean (Figure 141, C). The cocoon is suspended in the case, its 

 ends being attached to the wall of the case by longitudinal threads. The 

 larva which is ready for pupation (prepupa) assumes the typical posture 

 preparatory for the molt: the head is turned under and pressed to the 

 thorax, the forelegs are directed forward and the mid- and hind legs are 

 extended along the body. 



The cocoon is built by the same method in the family Glossosomatidae. 

 The cocoons of the preceding families are characteristic structures which 

 are not found in other families of Annulipalpia. 



The pupal case of Glossosomatidae consists of large sand grains 

 (Figure 143); it differs from the case of the larva in the absence of a lower 

 wall; in certain forms (Sy n a gap e t u s) the wall consists of coarser 

 material; the base of the case is attached to a stone by a broad band of silk 

 and is provided with ventilation holes. The form of the pupal cases of this 

 family resembles that of Rhy ac op hi 1 a, but they are much smaller 

 (8 — 10 mm in Glossosomatinae, 4-6 mm in Agapetinae). 



The larvae of some genera of Hydroptilidae (Ag ray lea, Oxyethira) 

 do not alter the larval case; before pupation, they attach the flat side of the 

 cases to the substrate by short strands of silk; these strands have disk- 

 shaped wide ends ("plates") (Figure 144); the anterior and posterior case 

 openings are covered with a thin membrane. Before pupation, the larva of 



96 



