THE SOLITARY WASPS
The ordinary wasps are acquaintances of every one, but the solitary or keyhole wasps are not so well known, although they are far from uncommon. They are little narrow black insects striped across the body with yellow, belonging to the genus Odynerus ([pl. A], 9), and might hardly be recognized as belonging to the same family as the true or social wasps. Still they have considerable powers of stinging, and fold their wings lengthwise when at rest like their larger relatives. I dare say some people may have noticed that a wasp's wing sometimes assumes a narrow straight form, quite unlike what it is when expanded. This is due to the wasp being able to fold its wing lengthwise like a fan. The wasp tribe are, so far as I know, the only stinging Hymenoptera which have this power.
They make their nests of mud, etc., in crevices of walls, in banks, in plant stems, and often
in most inconvenient places, such as keyholes, etc. Some of the solitary wasps have a very curious habit of making a tubular entrance to their hole. These may sometimes be seen projecting from sandy banks. The tube is composed of a series of little pellets of mud, which the wasp by degrees, with the help of its mouth secretions, sticks together till a sort of openwork curved tube of sometimes an inch long is formed (fig. 5). This curve is directed downwards, so that the wasp has to creep up it before reaching the actual orifice of the nest. It looks as if the first shower of rain would wash the whole structure away, and I have very little doubt that it often does so. The object of these tubes is difficult to appreciate. There is a bee on the continent which makes straight chimneys above its holes, so as to raise the entrance above the surrounding herbage; possibly these solitary wasps once required
their tubes also for some such purpose, and have continued on truly conservative lines to build them long after all usefulness has passed away from the habit; anyhow they are very interesting and beautiful structures. I have found the tubes of one of our rarer species projecting perpendicularly out of the level sand, but even then the tubes were curved over at the end, so that the wasp had to go up and down again before entering its actual hole. The Rev. F. D. Morice in 1906 found the tubes of the same species in numbers projecting from the walls of an old stuccoed cottage situated close to the locality where I found mine, so it is evident that more than one situation suits its requirements. The solitary wasps provision their cells with caterpillars, stinging them in the same way as the fossors do. One very peculiar genus, of one species only in this country, has its body much narrowed at the waist by reason of the constricted form of the basal segment; it makes a little round nest of clay which it suspends from a twig of heather or other plant. This species is rarely met with except on the heathery commons of Surrey, Hants, Dorset, etc. The
solitary wasps are subject to the attacks of cuckoos belonging to the jewel fly or Chrysis tribe; these behave differently from those belonging to the aculeate groups, as their larvæ do not eat the food laid up for the wasp, but wait till the wasp larva has finished feeding up, and then devour it. Unlike as these cuckoos are to their hosts in their brilliant metallic coloration, etc., they have structural characters curiously like theirs, so that even here a common parentage in bygone generations may be reasonably suspected. At present, however, they are placed, except by a few systematists, in quite distinct families of the Hymenoptera.
In general form these solitary wasps resemble the fossors more than the bees; they have mostly short tongues (I think all our British ones have), and their hairs are simple or more or less spirally twisted.