HYMENOPTERA. 163 



terials for the construction of their cases ; but they have 

 the power of employing almost any which fall in their way, 

 when there is a deficiency of those usually preferred. The food 

 of some of the larvce is vegetable ; but others prey upon small 

 aquatic larvse, such as those of the Neuroptera. When about 

 to assume the pupa state, the larvae fix their cases to some solid 

 substances beneath the water, and close the two extremities with 

 a kind of grating, that admits of the passage of water through 

 the tube, which is necessary for respiration. A short time 

 before they are to assume their perfect form, they make their 

 way out by means of the pair of hooked jaws, with which they 

 are then furnished, and swim about with great activity by means 

 of the two hind legs, crawling occasionally upon the four first. 

 In order to throw off their pupa-case, the larger species crawl 

 up plants out of the water ; but the smaller ones merely come to 

 the surface, and there undergo their transformation, using 

 their old envelope as a boat, out of which they rise to expand 

 their wings, much in the same manner as Gnats. The perfect 

 Caddice-flies run with great agility, but their flight is awkward, 

 except in some of the smaller species, which assemble in troops 

 and fly over the surface of the water towards sunset. They are 

 nocturnal in their habits, and not unfrequently enter our houses, 

 being attracted by the light. They emit a disagreeable smell 

 when touched. These insects are very numerous in Britain ; 

 no fewer than 190 species having been described. 



ORDER V. HYMENOPTERA. 



749. In the membranous character of their four wings, the 

 insects of this Order resemble the Neuroptera ; but they cannot 

 well be mistaken for them. The anterior wings are usually 

 much larger than the posterior ; and the veins or nerves * are 



* These terms are used to mean the same things; namely, the hard frame- 

 work on which the membrane of the wing is extended. They must not be un- 

 derstood as indicating any analogy to the veins and nerves of higher animals. 



