I was going to suggest you post here; your post on the fruit forum morphed into spider chat.

The picture is at a tough angle for ID; the bulbous thorax is throwing me, but it is known in some wasps.

That's exactly what I was going to say.....it's a very strange angle.

Sawfly? Go back and get more photos, or check your radiator grille. :)

This was eventually identified on a fruit forum as March Fly.

Looking through the many pictures of the many types of March Fly I found the match of the ones on my plum tree.