There are many thousands of species of wasps worldwide. Some form huge colonies of thousands, while others live a solitary lifestyle.
Solitary wasp females each build a small nest and stock it for their offspring only. They never form colonies with workers like the common social wasp. They feed mainly on nectar, although their young feed on other insects while in the larval stage.
Most wasp species are solitary, belonging to the Hymenoptera Order. They are called solitary because they do not form large colonies of a queen and male workers, characteristic of social wasps. Each solitary wasp female makes her own nest, or succession of nests, and stocks it with caterpillars or other larvae for the sole use of her offspring.
Solitary wasps, like social wasps, possess a sting they will use if attacked. However, only the stings of the larger species can penetrate the human skin.
Building The Nest
The potter wasp is a small black insect with some yellow markings. As with many other solitary wasps, it has a tapering stalk that joins the thorax and abdomen.
The nest of the potter wasp is joined to a piece of heather and can be easily recognized. The female scoops up small amounts of clay from the nearest available source and forms it into pellets with her mandibles and front legs, cementing them together with saliva.
The female uses the pellets to build a nest which, when complete, is shaped like a tiny rounded flask with a short neck and expanded mouth. The nest size varies according to the wasp species, but potter wasp nests are usually about the size of a thumbnail.
After building the nest in the characteristic pot shape, the female flies off, searching for small caterpillars. She is careful not to kill them but stings them in such a way as to paralyze them. Hairy caterpillars are never chosen, just smooth caterpillars, of a size small enough to fit inside the narrow neck of the nest.
The caterpillars are carried back to the nest for storage. Once a few have been collected, the female wasp lays a single egg which is suspended from the roof of the flask by a slender thread. The nest is finally sealed with a pellet of clay.
The caterpillars are eaten alive by the young. If they were killed, they would quickly decompose and become inedible. When the wasp larva hatches, it remains on its eggshell, feeding on the caterpillars without getting too close to their wriggling movements.
Later, when it is larger and stronger, the larva goes down among the caterpillars at the bottom of the nest. Once it has feasted on the caterpillars, it grows rapidly, becoming fully grown in about a week to ten days.
When fully fed, the larva pupates and the mature wasp breaks their way out through the top of the flask in the following summer.
The mason wasps are related to the potter wasps, and some of them also use clay to make their nests, but they show little architectural skill in doing so. The wall mason (Ancistrocerus parietum), a black and yellow wasp, builds cells of mud, often in the crevices of old walls.
It encloses several cells in a mass of clay, stocking each one, as it is completed, with small paralyzed caterpillars. Like the potter wasp, the wall mason deposits a single egg in the nest, then seals it up, taking no further interest in it.
Looking After The Young
The female of one species of sand digger wasp, Ammophila pubescens, makes single-chamber nests like other solitary wasps, but her behavior changes once built. She continues to visit and stock her nests after each one has been started with an egg and a single paralyzed caterpillar.
These nests contain wasp larvae in different stages of development. The female makes a morning inspection of all her nests and treats them during the day accordingly. If the egg has not hatched, she brings nothing to the nest. If there is a small larva, she brings up to three caterpillars during the day. If the larva is large, up to seven caterpillars may be brought to the cell for food. If the larva has completed its growth, the burrow is finally closed.
Attracting Solitary Wasps
Adult solitary wasps are not meat-eaters, feeding mostly on nectar instead. They do not have the long tongues of butterflies and get their nectar from open flowers such as cow parsley. Some species of solitary wasp will take advantage of ready-made holes or burrows.
To see these at close quarters, find a large log —preferably one with the bark removed—and drill several 4-7mm diameter holes. Stand the log up at eye-level in a sunny part of the garden. In spring and early summer, plenty of solitary wasps should inspect the holes, popping in and out of them to investigate them thoroughly. You may be lucky enough to see a nest form.
Two digger wasps you might see nesting in the log are Ectemnius cavifrons and Pemphredon lugubris. The former is a yellow and black wasp that preys on hoverflies, while the latter is black and hunts only aphids. P. lugubris is a lively insect whose name refers to its dark, somber coloring.
Another good way to attract wasps and other insects is to make an insect hotel.