322 THE BIOLOGY OF INSECTS 



sub-family. The genus Odynerus includes solitary wasps 

 in which there is no worker caste ; the females usually build 

 nests of earth or of hardened clay (Plate XI, B) wherein 

 they lay their eggs and deposit caterpillars to serv^e as food 

 for the grubs w^hen hatched. Odynerus and other genera 

 of the sub-family Eumeninae have elongate grooved 

 mandibles and a still longer labium ; the shin of each middle 

 leg has a single apical spine and the foot claws are toothed 

 or bifid. Vespa, the typical genus of the Vespinae, has 

 relatively short mandibles and a still shorter labium ; the 

 shin of each middle leg has two spines at the tip, and the 

 foot-claws are simple. Most of the Vespinae form true 

 social communities with a worker caste (as described in 

 Chap. IX, pp. 223-4, 234-6), and build nests of a paper 

 worked up from wood (Plates VII, VIII). The differences 

 in the jaws and legs mentioned as distinguishing Odynerus 

 and Eumenes on the one hand from Vespa on the other 

 are typical of the characters that are found to hold through 

 large series of related species, and are therefore of special 

 value in serving to define the genera in wdiich the species 

 are grouped. 



From the genus we may now pass to the species, and 

 the British Social w^asps (Vespa) may serve as examples of 

 specific distinction. The largest of them is the Hornet 

 (Vespa crahro) to be recognised not only by its size, but by the 

 predominantly brown hue of its body. Our other species 

 of Vespa all have the thorax black and yellow. Two of the 

 six — Vespa sylvestris and V. norvegica — are " long-cheeked " 

 wasps, with cheeks prolonged (Fig. 77, //) below the eyes 

 towards the bases of the mandibles, and with shins markedly 

 hairy. Both species build their nests in trees. Vespa 

 sylvestris has the face clear yellow with only a small central 

 black spot, while in V. norvegica there is a broad central 

 black streak. The other four — Vespa vulgaris^ V. germanica^ 

 V. rufa, and V. austriaca, all of which nest in the ground, are 

 ** short-cheeked," the base of the mandible close beneath 

 the eye (Fig. 77, g), and the shins clothed with short 

 hairs. V. vulgaris has usually a broad black band down the 



