156 GENERAL CHARACTERS OF HYMENoPTERA. 



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 Bri- 

 tain ; no fewer than 1 90 species having been described. 



ORDER IV. HYMENOPTERA. 



683. 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 

 much fewer in number than in the Neuroptera, and do not form a 

 close network by their ramifications, as in that Order. In some 

 of the minute species, the wings are almost, or even entirely, 

 destitute of nerves. Another character furnished by the wings 

 consists in the connection of the anterior and posterior wings on 

 each side, during flight, by means of a series of minute hooks 

 along the front edge of the latter, which catch the hinder mar- 

 gin of the other, so as to produce one continued surface on each 

 side. The principal character of the Order, however, is derived 

 from the structure of the mouth ; for, although considered as 

 mandibulate insects, the Hymenoptera are much better fitted for 

 imbibing their nourishment by suction, than for obtaining it by 

 mastication ( 614). The Hymenoptera are also peculiarly 

 distinguished by a prolongation of the last segment of the body 

 in the females, into an organ, which is, in one division of the 

 Order, a sting, and in the other, an ovipositor ', or instrument for 

 the deposition of the eggs, usually possessing the power of boring 

 a hollow for their reception. 



* 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 under- 

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



