politus, L.flavicornis, L.rhombicus) is possible only if the animal 



lives in water (Figure 75); when larvae are taken out of the water, they 



cannot move, 



The larvae of Molanna have a special type of movement: they move 



by leaps; these movements are achieved by a sharp downward inclination 



of head and thorax and by supporting the body with 

 the forelegs, and this results in a leap forward and 

 slightly upward; the wide wings of the case brake 

 the fall of the case; some observations indicate that 

 this braking effect lasts longer in young larvae with 

 a delicate case than in older larvae. The larva of 

 Molanna is very mobile and flexible; its move- 

 ments are agile, and when the larva is turned on 

 its back, it extends the body from the case, buries 

 its legs in the sand and restores the normal 

 position of the case with a sharp movement 

 (Figure 76). 



There are almost immobile case bearers, e. g., 

 the larvae of Brachycentridae, some of which 

 (Br a c hy c ent r u s subnubilis or Oligo- 

 plectrum maculatum) attach the case to 

 objects, using the legs with their numerous setae 

 and spines as sieves for the collection of prey 

 carried by flowing water. 



Some larvae can swim, e. g., the larva of 

 Triaenodes bicolor; the femora and tibiae 

 of the hind legs are densely covered with long 

 setae. The light, smooth and conical case of this 

 larva is built of fine, spirally arranged thin plant 

 fragments; the case hangs down when the larva 

 swims. The insect rows with its hind legs, 

 keeping the midlegs folded and the forelegs 

 extended forward. In the family Leptoceridae, 

 the larvae of Setodes tineiformis are good 

 swimmers; this species resembles Triaenodes 

 bicolor ecologically (Figure 77) and lives among 

 plants; it has natatorial legs and its case (which 

 consists of secretion) is lighter than that of 

 Triaenodes bicolor. 



Swimming is a rare phenomenon in the late 

 stages of development, but is common in young, 

 freshly hatched larvae; the specific weight of the 

 body with its not yet hardened integument is very 

 small; legs and setae are relatively long 

 (Figures 78—80); these characters make the young 

 larvae similar to plankton and enable them to 

 remain suspended in water for some time, and to 

 move actively but slowly by curving movements 

 of the abdomen. Because of this habit they do not 



FIGURES 76 and 77. Move- 

 ments of larvae of Integripalpia 

 in their cases (diagram): 



76 — turning the case of the 

 larva of Molanna in a trans- 

 verse (A) and longitudinal (B) 

 direction (after Dembovskii); 



77 — larva of Triaenodes 

 bicolor in swimming posi- 

 tion (after Hickin). 



47 



