STRUCTURE AND HABITS OF THE HYMENOPTERA. 



355 



COMMON WASP (Vespa vulgaris). 



from the apex of the abdomen, which subserve the purpose of conveying the eggs to the spot where 

 their development is to take place, and at the same time, in many instances, constitute formidable 

 offensive weapons. These are the ovipositors, or stings, the parts composing which must be regarded 

 as appendages of the concealed terminal segments of the abdomen. The latter are represented by 

 movable plates, to which the main piece of the protrusible organ is attached, and also furnish 

 sheathing-pieces, often of considerable length, which seem to sei've as supports to the latter during 

 the act of penetration. In the great majority of the Hymenoptera the 

 ovipositor, or sting, consists of a single middle principal piece, deeply 

 grooved along its lower surface, and of a pair of slender lancets, which 

 rest against the edges of the middle piece and against each other in the 

 middle line, so as to close up the groove in the single piece, and convert it 

 into a canal. With this canal the oviducts are connected at the base of the 

 organ, so that when its point has been forced a sufficient distance into the 

 proper nidus for the development of the young, the eggs can readily pass 

 to their destination. In the case of those insects in which the organ is converted into a sting, all the 

 parts are exceedingly acute, and the base of the organ is put in communication with a peculiar gland 



secreting an acrid fluid, which contains much formic acid, and it is the 

 injection of this fluid into the puncture produced by the sting that makes 

 the effects of being stung by a Bee or a Wasp so exceedingly painful. 

 The stings of these animals are not, however, to be regarded as exclu- 

 sively intended as weapons of war. A very great number of them 

 require to provide their young with a supply of animal food, which 

 consists generally either of the larvae of other insects or of Spiders. 

 To render these victims helpless and incapable of making their escape, 

 the mother stings them before depositing them with her egg in the nest 

 she has prepared, and by this means they are paralysed, although they 

 can still live for a considerable time. The larva kills them as he wants 

 them, and thus a supply of fresh provisions is secm'ed for him during 

 the whole course of his development. The above may be taken as a 

 general description of the character of the ovipositor in the great 



majority of the Hymenoptera. It is departed from only in one family, that of the Saw-flies 

 (Tenthredinidai), as will be noticed in the character of that group. 



Of the internal structure of the Hymenoptera we need not say much, but there are certain 

 peculiarities which should be noticed. The alimentary canal is generally of moderate length ; the 

 malpighian vessels are short and numerous ; salivary glands, opening into the mouth, occur in 

 most species, and attain a particularly lai'ge development in those which have to build cells for 

 the rearing of their larvae ; and the two hinder ganglia of the thorax are united into a single 

 mass, Avhile the ventral chain usually has five or six ganglia. A structural character connected 

 with the great power of flight generally possessed by these insects is the great enlargement of 

 main tracheal stems, which are dilated in the abdomen into very large air-sacs. 



In their habits the Hymenoptera are diurnal, most of them flying about actively in the 

 hottest sunshine in search of the flowers upon the sweet juices of which they chiefly live in the 

 perfect state. The working Ants and the females after their nuptial flights, and some few species 

 of other families, are destitute of wings, and can only crawl upon the ground or on plants; but 

 these are active during the day like their more favoured relatives, and the Ants usually retire into 

 their nests and shut themselves up there when night comes on. 



In the habits of the larvae there is great diversity, notwithstanding great general uniformity of 

 structure. Except in one division of the order, the larvae of these insects are soft, footless creatures, 

 which would be called maggots but for their possessing a hard, horny head. In the Saw-flies and 

 Tailed Wasps, which differ in several important particulars from the rest of the order, the larvae generally 

 resemble Caterpillars (see figure above), possessing three pairs of thoracic limbs, more or less developed ; 

 and in the case of the greater number, whose larvae feed openly upon the leaves of plants, also 

 several pairs of abdominal pro-legs. The maggot-like grubs (see figure on p. 356), which always live 



LAKY A OF SAW-FLY. 



