Aquatic Insects 



197 



adult dragonfly, that dashes about in the air on shim- 

 mering wings, is the sluggish silt-covered nymph, that 

 sprawls in the mud on the pond bottom ! How unlike 



the fluttering fragile caddis -fly is the 

 caddis-worm in its Itimbering case ! 



As with terrestrial insects, so with 

 those that are aquatic, there are 

 many degrees of difference between 

 young and adult, and there are two 

 main types of metamorphosis, long 

 familiarly known as complete and 

 incomplete. With complete meta- 

 morphosis a quiescent pupal stage is 

 entered upon at the close of the 

 active larval life, and the form of 

 the body is greatly altered during 

 transformation. Adults and young 

 are very unlike. Caddis- worms, for 

 example, the larvse of caddis-flies, are 

 so unlike caddis-flies in every exter- 

 nal feature, that no one who has not 

 studied them would think of their 

 identity. 



The caddis-fly shown in the accom- 

 panying figure is one that is very 

 common about marshes, where its 

 larva dwells in temporary ponds and 

 pools. Often in early summer, the 

 bottom will be found thickly strewn 

 with larvae in their lumbering cases. 

 Then they suddenly disappear. 

 They drag their cases into the shelter 

 of sedge clumps bordering the pools, 

 and transform to pupae inside them. A fortnight later 

 they transform to adult caddis-flies, and appear aii 

 shown in figure 103, pretty soft brown insects marked 

 with straw-yellow in a neat pattern. The larva is 

 of the form shown in figure 104, a stocky worm-like 



Fig. 103. Caddis-fly. 

 {Limnophilus sp.) 



