This week I want to introduce you to wasps of the genus Ectemnius.

Ectemnius are one of my favourite solitary wasps and I always look forward to summer when they are on the wing. Solitary wasps, as their name suggests, are solitary creatures. The female emerges when the time is right and once mated will spend the rest of her life alone, choosing and excavating her nest site, hunting and providing a safe place for her vulnerable brood to develop into next year’s wasps.

Ectemnius are very striking looking, medium to large-sized wasps with black and yellow markings on the abdomen. Depending on gender and species they range anywhere from 6 to 17mm long. They have quite boxy, square-shaped heads with large compound eyes that converge on the inner edges and some males have a series of bumps on the first few segments of the antennae. Depending on species, they have either silvery or golden hairs just above the mandibles on the part of the face called the clypeus, making them very handsome-looking wasps indeed!

Most UK species nest in rotting or decaying wood, although Ectemnius rubicola has a preference for the stems of herbaceous plants such as brambles or reeds. In common with other wasps that excavate their nests in wood, Ectemnius have broad, highly modified mandibles ending with a series of ‘teeth’ which they use to scrape out the tunnels and chambers in which they create their nests. One of my favourite observations of these wasps was watching a female excavating her nest and kick out an extraordinary amount of sawdust for one small wasp!

Their nests are typically constructed with one main entrance with a number of tunnels branching off and their cells are partitioned with sawdust. Ectemnius hunt various Diptera (flies) to stock their nests and feed their young. At suitable sites, Ectemnius will nest in numbers in what are called aggregations but each female wasp will create and provide for her own young independently, however, Ectemnius cephalotes will often share a nest entrance, but will then tend their own individual nests. 

Ectemnius are mainly summer flying wasps and to watch one hunt is a real treat! Their large compound eyes play a very important role in locating prey, and according to Lomholdt, author of The Sphecidae (Hymenoptera) of Fennoscandia and Denmark, are probably sharp-sighted at about 15 - 20cm, relying on their sense of smell and touch at shorter distances once the prey has been caught.  On locating their prey they hover, almost unmoving, with a series of short, jerking movements thought to be associated with the estimation of distance. Then a sudden, darting movement towards the prey, seizing it with its mandibles and legs. The wasp then paralyses its prey and carries it back to the nest by clutching it beneath their bodies with their legs. Prey can often be just as large or even larger than the wasp itself! 

If you would like to attract these interesting wasps into your garden then stack up logs or rotting wood in a sunny position, and plant wild carrot, hogweed, wild parsley, or one of the other members of the umbellifer family.

If you would like to learn more about these fantastic wasps please check out the BWARS website for further information on individual species.