Ichneumonid wasp

Levi spotted an enormous wasp in one of our pecan trees Sunday (the one his tire swing is hanging from).  Upon closer inspection I discovered it was a female with an incredibly long ovipositor laying eggs inside the tree.  We were there again yesterday & saw a large group of females all laying eggs.  

I had to go grab the camera!  

I knew they were Ichneumonid (thin waist) wasps, but that was about it.  After a little research, there's a really cool story:

The wasp we saw is Megarhyssa macrurus.

These enormous Ichneumonid wasp parasitize pigeon horntail (another huge wasp) larvae. What looks like a long stinger is the female's ovipositor which she uses to lay her eggs into the horntail larvae, which bore tunnels in decaying wood.  Female Megarhyssa macrurus are able to detect these larvae through the bark, and lay their eggs on them; within a couple of weeks, the Megarhyssa larvae will have consumed their host and pupate. They will emerge as an adult the coming summer.

In all my reading I never found mention of a large group of females all laying in the same tree at the same time.  There must be a great concentration of horntail larvae in this particular tree.  At one time yesterday there were 5 females congregated.

two females - the one on the right is pushing her ovipositor in - it is looped up in the air, it's so long

I did this one at a distance so you can see the entire ovipositor - it's twice the body length of the wasp.