SOME AQUATIC INSECTS 95 



their somewhat shambling gait still further re- 

 minding one of a decrepit " old-clo' " man. The 

 cases are made with the aid of silky threads, with 

 which the Caddis larva weaves together the 

 material, bits of stick, leaves, shells, etc., which it 

 collects for the purpose ; the supply of silk being 

 produced by special silk-secreting glands which 

 have their opening in the labium of the insect. 



When the Caddis larva is full grown, it makes 

 ready for its change into the pupal state by 

 shortening and partially closing each end of its 

 case with silk and plant debris, or small stones. 

 It may also at the same time considerably 

 strengthen its case, and anchor it for greater 

 safety to a stone or submerged plant-stem. 

 Pupation then takes place, and lasts for a vary- 

 ing period in the different species, the pupa or 

 nymph ultimately breaking out of its case and 

 quitting the water, in order that the perfect, 

 winged Caddis-fly may safely emerge. In some 

 of the smaller species the pupae do not leave 

 the water, but rise to the surface and float there, 

 so that the perfect insect makes its escape in a 

 similar manner to the Gnat. The construction 

 of a case by a Caddis larva is a very interesting 

 sight, and one that may be easily witnessed. 

 The larva must be carefully removed from its 

 case without injury. This will be best accom- 

 plished by gently slitting or breaking open the 

 case with the help of a pair of micro-forceps. 

 It is quite useless to attempt to pull the larva 

 head-first out of the case, for the insect will 

 generally rather be pulled to pieces than relin- 

 quish its hold upon the silken lining of its tube. 



