226 The Orders of Insects 



and a variable number in the males. The mesothorax 

 is the largest segment of the fore-body. The legs have 

 large haunches which are inserted close together; this 

 character readily separates Caddis-flies from Stone- 

 flies to which they bear a distant superficial like- 

 ness. There are nine evident segments in the 

 abdomen, the hindmost, in the male, bearing a pair 

 of claspers (3). 



Habits and Development. — Caddis-flies are feebly- 

 flying insects, often nocturnal in their habits and fre- 

 quenting the neighbourhood of the waters wherein 

 their preparatory stages are passed. The female drops 

 her eggs, which are enclosed in a jelly-like substance, 

 into a pond or river. The larvae are intermediate 

 between the campodeiform and cruciform type ; the 

 thoracic segments — each bearing a pair of legs — 

 are partly chitinised like the head ; while the ten- 

 segmented hind-body is soft and bears thread-like 

 tracheal gills. The tail-segment is provided with a 

 pair of hooks whereby the larva clings to the inside 

 of the protective case which it builds by cementing 

 various foreign objects — sticks, stones, shells, etc. — 

 with the secretion of its spinning-glands. Most of 

 the larvae or "caddis-worms" feed on water-plants, 

 but some devour other insects, etc. When full- 

 grown the larva closes up both ends of its case and 

 changes into a free pupa, closely like the imago, 

 except for the presence of strong mandibles. By 

 means of these the pupa is able to bite its way out 

 of the case and rise to the surface of the water ; after 

 emerging into the air the final moult is undergone 



(3, 170). 



Caddis-flies are distributed in all parts of the world. 

 They have been divided into seven families, which are 

 discriminated by somewhat small structural characters 

 (138). 



