Gasteruption jaculator

I was standing watching a dead sycamore in the garden (as you do), holding a camera (as you do), when this little beast landed in front of me.  It is a female Gasteruption jaculator, a parasitoid wasp, and it was checking the woodworm holes for signs of a likely host.

Parasitoidism is a type of parasitism characterised by a fatal outcome for the host, making it in between parasitism and predation.  A Gasteruption wasp lays its egg in or on the larva of a solitary bee or wasp and its own larva consumes the host larva and its food supply.  This one was sniffing the holes with its antennae to locate a target.

The long white-tipped spike at the back is a sheath covering its ovipositor.  Once it was satisfied it had located a target it unsheathed the ovipositor which comes out half way along.

Next it manoeuvred the ovipositor into the hole.

The hole was very deep so it had to push in the whole length of the ovipositor and then reverse in the whole of its body, leaving only its antennae protruding.

Deep in the hole it laid its egg on the host's larva.  Once the deed was done, which took only a few seconds, it climbed out of the hole and flew off.  I didn't get to see how it resheathed its ovipositor.

The whole process was very quick but was amazing to watch.  The scale is extraordinary - the woodworm hole is less than 2mm across so the gasteruption eggs must be minute to fit down the ovipositor.