Thank you so much Ken! This has got to be right. No wonder I couldn't figure it out... these things are really bizarre! There's another image under genus Megaxyela that is extremely close to mine , and it even lists hickory and pecan as hosts on the guide page. If I'd had any idea I was looking at something so unusual, I would have taken a lot more pictures.

Do you think I'd be justified in moving these images to Megaxyela, or should I play it safe and keep them at a higher taxa?

Edit: Here's another example of Megaxyela I found by doing a Google image search.

and there could be other similar sawflies out there of which I am unaware, I don't feel confident recommending a move to the genus level. If they were my pics, I'd probably leave them in ID Request for a day or two and, if no expert had commented by then, move them to Sawflies, Horntails and Wood Wasps .

But that's just my personal opinion. It's really your call.