Deadly Assassin

A few weeks ago I collected a bedeguar gall (aka Robin's pincushion gall) to see if I could hatch out the tiny gall wasps, called Diplolepis rosae, that cause these weird growths on wild roses (click here for pictures of the gall).

So far no gall wasps have appeared, but this little ichneumon wasps has.  It's called Orthopelma mediator and it's the only ichneumon that parasitises British gall wasp larvae. It's about 4mm. long and this is a male - the female has a needle-like ovipositor on the end of her tail, like an assassin's stiletto (see last photograph).

O.mediator lays its eggs in the larvae of Diplolepis rosae before the gall forms, then the parasite's larvae feed on the internal organs of the gall wasp larvae within the gall, until nothing is left but the host's skin and jaws. It may be that all the gall wasp larvae have been parasitised, but so far only two of the parasites have emerged from the gall.

I've constructed a little chamber for photographing tiny insects like this, made from two microscope slides with a spacer in between, which seems to work pretty well - although the lighting (flash) needs a bit or work. The trickiest stage is coaxing the insect into the narrow gap between the slides,

This is a female, with her lethal ovipositor extended


Sixteen insect species, including parasites, hyperparasites and inquilines live in bedeguar galls, together with the gall wasp larvae. One down, fifteen to go......