The Eumenidae, or solitary wasps, are very little noticed by the ordinary observer, but they are nevertheless more numerous than the social Vespidae, about 800 species being known. In Britain we have sixteen species of the solitary, as against seven of the social wasps. The Eumenidae exhibit a considerable diversity in form and structure; some of them have the pedicel at the base of the abdomen very elongate, while in others this is so short as to be imperceptible in the ordinary position of the body. A repetition of similar differences of form occurs in the social wasps, so that notwithstanding the difference in habits there seems to be no satisfactory way of distinguishing the members of the two families except by the structure of the claws and tibial spurs. [Illustration: Fig. 27.—_Eumenes flavopicta_ ♀. Burma. The wings on the left in the position of repose, to show folding.] Fabre has sketched the habits of a species of _Eumenes_, probably _E. pomiformis_. This _Eumenes_ constructs with clay a small vase-like earthenware vessel, in the walls of which small stones are embedded (like Fig. 28, B). This it fills with food for the young. The food consists of caterpillars to the number of fourteen or sixteen for each nest. These caterpillars are believed to be stung by the parent-wasp (as is the case in the {73}fossorial Hymenoptera), but complete evidence of this does not seem to be extant, and if it be so, the stinging does not completely deprive the caterpillars of the capacity of movement, for they possess the power of using their mandibles and of making strokes, or kicking with the posterior part of the body. It is clear that if the delicate egg of the _Eumenes_ or the delicate larva that issues from it were placed in the midst of a mass of this kind, it would probably suffer destruction; therefore, to prevent this, the egg is not placed among the caterpillars, but is suspended from the dome covering the nest by a delicate thread rivalling in fineness the web of the spider, and being above the mass of food it is safe. When the young larva leaves the egg it still makes use of the shell as its habitation, and eats its first meals from the vantage-point of this suspension; although the mass of the food grows less by consumption, the little larva is still enabled to reach it by the fact that the egg-shell splits up to a sort of ribbon, and thus adds to the length of the suspensory thread, of which it is the terminal portion. Finally the heap of caterpillars shrinks so much that it cannot be reached by the larva even with the aid of the augmented length of the suspensory thread; by this time, however, the little creature has so much increased in size and strength that it is able to take its place amongst the food without danger of being crushed by the mass, and it afterwards completes its metamorphosis in the usual manner.