HYMENOPTERA > APOCRITA | Parasitica > Evanioidea > Gasteruptiidae

This family of small elongate parasitoid wasps are recognisable from their distinctive neck-like propleura, slender subclavate (club-shaped) metasoma, and swollen hind tibia.

The British list includes five species all in the genus Gasteruption. The males can't be reliably identified from photos, which probably explains why the NBN Atlas database includes quite a few records for the genus, rather than the actual species. The most frequently recorded species is Gasteruption jaculator, albeit with just one solitary record from Dorset back in 1996. The only other species that's likely to be found according to the distribution data I've seen is Gasteruption assectator. There are just under fifty confirmed sightings with most recent records coming from Wales although, interestingly, there are three from Dorset.

Fortunately, the females of these two species are easily separable by the length of their ovipositor, which in Gasteruption jaculator is very long as can be seen in the following photos, whereas in Gasteruption assectator it's very short.

Gasteruption jaculator is described as having a black rounded head and elongated thorax, slender abdomen with reddish- orange markings, and swollen hind tibia. The female’s ovipositor is usually very long with a white tip. When in a resting position, they have a habit of slowly and rhythmically raising and lowering their abdomen. Adults can grow up to 17mm long, and can normally be seen from May through to September as fresh specimens emerge from the nests of different hosts.

They were previously regarded as ectoparasitoids, but are now considered to be secondary cleptoparasitoids of food stored by solitary bees. The female uses her long ovipositor to penetrate the bee’s nest and lay an egg on the host larvae. After hatching, the wasp larvae will eat both its host and the food supply that the bee has collected.  

Updated, March 25 (v.2)