Elm Argid Sawfly Larvae

Caterpillar(?) on elm
I love your site. It’s helped me ID a number of crawly friends around my yard. But now I’ve got one I can’t ID. I live in Northborough, MA and I found these chewing away on a sprouted stump in my yard which I think is some sort of elm; it’s got a lot of greenery, but none over about 6ft up. Most of them are feeding all together on one or two hand-sized leaves at a time, and they’re eating the entire leaf except the central supporting vein, and even some of that too, before moving on to the next. The prolegs appear to almost be vestigial; I saw one of them relocating and it curled its abdomen around the twig more like a monkey’s tail to creep forward on it’s front legs. Can you help me ID them? Thanks!
Karen

Hi Karen,
We are nearly certain these are Elm Argid Sawflies, Arge scapularis, as pictured on BugGuide. At the very least, they are probably in the genus Arge. The larvae of many species look very similar.

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