Solitary wasps and gall 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.

Pompilidae

Pompilidae, robber wasp, spider wasp

Above is a wasp in the Pompilidae family. There are 5000 species of Pompilids in the world, mainly concentrated in the topics; with just 44 British species. In the U. K. they are usually seen in sunny weather, and this one was found hunting for spiders on rose bay willow herb and cow parsley. Note the conspicuous colours to the antennae.

Specidae

Above 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. The prey is then put in the cell with the egg so that when the larva hatches it will have fresh meat.

Ammophila sabulosa

Ammophila sabulosa, sand wasp, digger wasp, adult

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.

Cynipidae family - gall wasps.

Most species in this family induce gall formation in plants giving them their common name of gall wasps.

There are around 2000 described species world wide, and 91 British species, all are small.

Each species induces its own characteristic gall e.g., Robin's pincushion on the leaves of roses is caused by Diplolepsis rosae. The most common food plants of gall wasps in Europe are oaks and roses.

The presence of the larva causes the plant tissue to grow in a particular way to provide food and shelter for the larva. Many of the galls become parasitised by other wasps, especially those in the Ichumonidae (see above) family. The galls usually mature in late summer or early autumn.

Oak marble gall wasp

Adleria kollari, marble gall wasp

Above is the adult marble gall wasp, Adleria kollari, also known as Andricus kolleri. It produces spherical, single-celled, waxy galls on oak that are green at first, then turn a reddish brown, below.

Oak marble gall, Andricus kollari

The gall is formed on the leaf buds of the oak. The female wasps usues her ovipositor to inject an egg into the leaf buds. The resulting gall is a chamically-induced distortion of the leaf bud. At first the gall is green, later turning brown and growing hard, measuring around 25 mm in diameter.

The wasps were introduced into the U. K. in the 1830s in Devon. Like the Spangle gall, below, there is a sexual alternation of generations, and the whole cycle can take two years to complete in colder areas. The marble gall develops from an egg laid by a female wasps that has mated. Each marble gall contains a single larva and all are female. When these females emerge as adults from their gall they do not mate, but lay an unfertilised egg in the leaf bud of the non-native Turkey oak. These galls develop over winter, and the larva inside grows and develops and emerges as an adult the following spring. Both males and females emerge from the galls on the Turkey oak. These adults mate, and the female continues the cycle by ovipositing an egg inside the leaf bud of a native oak.

Spangle gall wasp

Spangle gall, Neuroterus quercusbaccarum

Above are the galls on the back of an oak leaf caused by the Spangle gall wasp Neuroterus quercusbaccarum. The wasp itself is tiny, measuring about 3mm long. A single leaf can have as many as 100 galls with each gall containing one wasp larva. The larva feeds all through the autumn and winter. And emerge as adult wasps in the spring. The galls are slightly hairy, and are yellow-green at first, then change to dark red later. Usually the gall drops off the leaf before the leaf drops off the tree. Galls still on fallen leaves are less likely to develop. Fallen galls are eaten by thrushes and wood pigeons.

The lifecycle of these wasps is quite complicated. The adult wasps that emerge from the spangle galls lay eggs that form berry or currant galls, often on catkins. These galls measure 4 - 7 mm and look like a redcurrant. The adult wasps that emerge from the currant galls lays an egg on the underside of the oak leaf that forms the spangle galls. The wasps that emerge from the currant galls are male and female, and go on to mate. The wasps that emerge from the spangle galls are all female, and reproduce parthenogenically.

Spangle galles are not considered a problem on healthy trees, although a heavy infestation may cause a pause in growth of a young tree. The larva secretes chamicals that induce gall formation.

Eumenidae, mason or potter wasps

Odynerus sp., Family Eumenidae, maso/potter wasp

Above is a mason wasp Odynerus sp., and below 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.

nest entrance of odynerus (mason) wasp

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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