Much more variety exists in wasps' nests than would be supposed probable; those formed by some of the tropical species of Vespidae are enveloped in so solid and beautifully constructed an envelope of papier-maché, that they resist with complete success the torrential rains of the tropics; while some of those found in our own country are made of extremely soft and delicate paper, {81}which is probably chiefly glandular products. Our British Vespidae number only eight species, all belonging to the one genus Vespa, and yet they exhibit three different modes of nidification. _Vespa vulgaris_, _V. germanica_ and _V. rufa_ form subterranean nests, while _V. arborea_, _V. sylvestris_ and _V. norvegica_ suspend their habitations from the branches of trees, bushes, or strong annual plants. _Vespa crabro_, the hornet, usually adopts an intermediate course, forming its nest above ground, but in a spot where it is protected and concealed. The favourite habitat of this formidable Insect is the interior of an old tree, but the hornet will sometimes avail itself of the protection of a thatched roof. Both it and other arboreal species are said, however, to occasionally make subterranean nests. It is ascertained that _V. austriaca_, the eighth species, is an inquiline. [Illustration: Fig. 32—Nest of (?) _Polybia_ sp. The envelope partly cut open; _o_, entrance. (After de Saussure.)] De Saussure,[42] the monographer of the social wasps, classifies them according to the architecture of their nests. He establishes three groups: (1) Stelocyttares, in which the layers of comb are not connected with the envelope, but are supported by pillars made by the wasps (Fig. 31); (2) Poecilocyttares, an unsatisfactory group of which the chief characteristics appear to be that the nest is always covered by an envelope, and the comb is supported by an object such as the branch of a tree, round, or on, which the envelope is placed (Fig. 32); (3) Phragmocyttares, in which the layers of comb are supported, in part or entirely, by the envelope of the nest, communication being effected by a hole in each layer of the comb (Fig. 33). de Saussure's classification is far from satisfactory. There are many social wasps that construct nests destitute of any proper envelope; as an example of this, we may mention the species of {82}the abundant genus _Polistes_; these Insects make hexagonal cells, of paper-like material, forming an irregular comb, or mass, attached to bushes by a stalk near its centre; these nests are placed so that the mouths of the open cells look downwards. The species of _Ischnogaster_ (Fig. 34) make layers of comb, connected by a pedicel, but without any envelope; these Insects form a section of Stelocyttares called Gymnodomes.