Sabre wasp

This is a sabre wasp aka giant ichneumon Rhyssa persuasoria.The last time I saw one of these was 56 years ago, when I tried unsuccessful to photograph it with the first camera I ever owned. I found this one in our conservatory a few days ago.

It's about three inches long, and half of that is accounted for by that long ovipositor (egg-laying tube), which is used for drilling into wood and laying eggs on insect grubs that are tunnelling, unseen, inside.

That sword-like tail is really a scabbard, protecting the ovipositor which is only about as thick as a horse hair but has a tip that's strengthened with accumulated metals, that allows it to drill through wood.

Rhyssa persuasoria finds its hidden prey with the help of those long antennae, which can detect the smell of frass that accumulates in the tunnel behind its prey as it chews its way through timber.

Once an egg has been laid and hatches, the ichneumon larva slowly eats its prey alive.

The usual host of Rhyssa is said to be the grub of the giant wood wasp aka giant horntail Urocerus gigas, but I suspect that it may also lay its eggs on other wood-boring insect larvae. 

There are several wood piles under the edges around our garden, specifically build for insects that breed in decaying wood, from trees that I have had to cut down over the years, so maybe that is what attracted this spectacular parasitoid to our garden.