Unknown Sawfly Larvae really is Birch Sawfly

What type of caterpillar is this?
I’m hoping you folks can help me identify the type of caterpillar in the photo I’ve attached. They’re ravaging my white birch tree! That aside, I just want to ensure for the most part that it’s safe for my kids to play around the tree. Thanks,

Hi Christian,
These are not caterpillars, but Sawfly Larvae. Sawflies are non-stinging relatives of wasps. They will not harm your children, but might defoliate your tree if they are plentiful enough. We tried to identify the species, or even genus, but were unable to do so, despite locating a wonderful website devoted to Sawfly Larvae. We got excited when we read the description of the Birch Sawfly, Arge pectoralis, because the coloration matched, but the images on BugGuide show a very different body shape.

Hi Daniel,
Well, you can get excited again! See the attached image. My picture is out of focus, however the body shape is the same. I noticed that they go into that ‘S’ shape whenever any other bug, or my finger, approached it. Thanks for your help,

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