The illustration at p. 90 represents a completed nest of _V. germanica_. The rough, thick covering is seen outside, and within are the tiers of cells, each layer being supported by pillars from the layer immediately above. These pillars are always formed at the angle where these cells touch each other, so as to obtain as strong a foundation as possible. Only a very small space is left between the combs, just enough room, in fact, for the nurse-wasps to pass as they feed the young. The reader will remember that the young wasps all hang with their heads downwards, being held in their places by a sort of clasper at the end of the tail.]
When the foundress-wasp has completed a certain number of cells, and deposited eggs in them, she soon intermits her building operations, in order to procure food for the young grubs, which now require all her care. In a few weeks these become perfect wasps, and lend their assistance in the extension of the edifice; enlarging the original coping of the foundress by side walls, and forming another platform of cells, suspended to the first by columns, as that had been suspended to the ceiling.
[Illustration: Section of the Social-Wasp's Nest.
_a a_, the external wall; _b_, _c c_, five small terraces of cells for the neuter wasps, _d d_, _e e_, three rows of larger cells for the males and females.]
In this manner several platforms of combs are constructed, the outer walls being extended at the same time; and, by the end of the summer, there is generally from twelve to fifteen platforms of cells. Each contains about 1060 cells--forty-nine being contained in an inch and a half square, and, of course, making the enormous number of about 16,000 cells in one colony. Réaumur, upon these data, calculates that one vespiary may produce every year more than 30,000 wasps, reckoning only 10,000 cells, and each serving successively for the cradle of three generations. But, although the whole structure is built at the expense of so much labour and ingenuity, it has scarcely been finished before the winter sets in, when it becomes nearly useless, and serves only for the abode of a few benumbed females, who abandon it on the approach of spring, and never return; for wasps do not, like mason-bees, ever make use of the same nest for more than one season.