This is the male wasp. He showed up first. The males wait for the females to find this log and lay eggs in the larvae of the horn-tail wasps. Thanks for letting us know what’s inside! Luckily, this post is not load-bearing and is temporary.
The males are big. About 2.5 inches. The female is huge: 3.5 or so. She has a long ovipositor that looks like a ferocious stinger. Intimidating but not aggressive. She showed up a few days later and started carefully exploring the post, tapping and moving along slowly. There were dozens of males to a handful of females.
When she found the spot where the larvae were snuggled, she started drilling into the wood with her ovipositor. Her rear end sort of flipped inside-out and the ovipositor forked on either side of her abdomen. (The pictures would be better had I not been completely freaked out by the sight of her!)
The drill took only 5-10 minutes.
Then she deposited her eggs in the horn-tail wasp’s larvae. And took off. The males buzzed around for days afterward, waiting for the young females to emerge. We missed the hatching, sadly.
So many little (and big) wonders to see and learn from surround us.
End of lesson.