Solitary wasps

There are around 2,400 species of solitary wasps recorded in Britain and Ireland, many are parasitic, and some are used in controlling pest insect species.

Ichneumonidae The family Ichneumonidae contains the tiny parasitic wasps. There are over 60 000 species world wide, and over 2000 British species. All have long antennae with usually more than 16 segments, slender bodies, and very simple wing venation (see left and below). The adults usually feed on nectar from flowers and honeydew from aphids. The females usually have visible ovipositors. Their larvae are usually parasitic in or on other insects; mainly butterflies, moths, sawflies and beetles, and are major agents of pest insect control. Few are parasitic on a single species; usually they parasitise a group of species. The female usually lays her egg inside the victim, but some species lay the egg on the surface of the victim's body.

Rhyssa persuasoria, the sabre wasp, locates grubs of the wood wasp by detecting the presence of a particular fungus injected by the female wood wasp at the same time as she inserts the egg. She has an ovipositor almost 4 cm long, though her body length is 20 - 35 mm, making her the largest Ichneumonid in the U. K. It takes around 20 - 60 minutes to drill down into the 3 cm of wood to where the wood wasp larva is located. During this time the wasp is in a very vulnerable position with no protection from predators. Adults are black with white spots and red legs, and fly from June - September. A fully grown larva can reach 25 mm long.

Most overwinter as grubs in the host, or as pupae; just a few overwinter as adults, and of these it is only the females that do so. All the adult males die with the approach of cold weather.

Ichneumon suspiciosus is black with a yellow patch near the top of the abdomen. The legs are black except for the tibia and tarsi which are yellow. Adult body length is 10 mm.

The larva is an internal parasite of caterpillars.

It is seen in the summer, often on umbellifers.

Specidae

On the right is Ammophila sabulosa, a sand or digger wasp. It is in the family Specidae, of which there are 8000 species world wide and 115 species in Britain.

Sphecids are solitary wasps. Their wings are held flat over the body when at rest, and their flight speed has been recorded as 1.5 metres per second (compare this with other insects).

They range in size from 0.4 - 5.5 cm long. The females catch insects or spiders to feed their larva. They sting the prey to paralyse it, but not kill it. This is then put in the cell with the egg so that when the larva hatches it will have fresh meat.

Ammophila sabulosa

Ammophila sabulosa is black except for the middle part of the abdomen which is red or orange. It is usually found near pine trees and sandy soil which is where the female digs a burrow, and is most often seen in the UK in June and July.

Each burrow takes an hour or two to dig, Once the burrow has been dug she selects a pebble just big enough to rest over the top of the burrow, then she goes off to search for a caterpillar. The larvae are fed on caterpillars. The caterpillar is too big for the wasp to fly with, so usually she carries it beneath her or drags it to the burrow which she has already dug. She is capable of dragging a caterpillar 11 times her own weight back to her burrow. When she returns with the caterpillar she removes the pebble and drags the caterpillar into the burrow. Usually there is one cell, one egg and one caterpillar per burrow.

The female searches for caterpillars on pine trees or other vegetation. Once the caterpillar and egg are safely in the burrow the female will often camouflage the entrance by dragging twigs or pine needles over it.

She will supply several burrows, each with a larva at a different stage of development, so she must remember their positions and estimate when the food for each will run out.

Eumenidae, mason or potter wasps

On the right is a mason wasp Odynerus sp., and on the left is a typical nest. There are over 3000 Eumenidae world wide, and in the UK there are 22 species. They are commonly known as mason or potter wasps.

Masons usually provision their nests with beetle larvae or caterpillars. The adult wasps feed on nectar. The adults have strong jaws. The nests usually have curved towers made from the materials excavated from the sandy banks or soft mortar which are their preferred nesting sites (see drawing on the left).

The nests contain several cells with one egg per cell. As with all mason wasps the adults never see their offspring. Excavated fragments which are not used in constructing the tower are often carried some distance away from the nest site so that there is no tell-tale pile of rubble at the base of the wall/bank.

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The perils of pollination

The hammer orchid in Australia mimics a wingless female wasp. When she is ready to mate the female wasp climbs up a flower and releases a perfume to attract a mate. The mate flies in (males have wings) and carries the female off to mate on the wing. After mating he deposits the female on a stalk or a flower.

The hammer orchid has a small flower on a long stalk. The flower is in two parts hinged together. One part resembles the female wasp, and the other is a pad with two pollen sacs. The male wasp lands on what he thinks is a female, then tries to take off on the mating flight, but he cannot. The hinge catapults him against the pollen pad, and this happens at every attempt he makes to take off with what he thinks is a female wasp.

After a few hits the pollen sacs peel off the anthers and stick to the back of the male wasp. The pollen sacs are so placed that another orchid will be fertilised when he repeats the process. The flower succeeds in its deception by flowering a few days before the female wasps emerge. If it flowered as the females were emerging the males would not be deceived, so good timing is essential.