Oregon Hikers

I have NO idea what these little beasties are. They're probably larvae/nymphs of some sort, but they might not even be insects. (Definitely arthropods of some sort, though.) I found them last spring in a tidepool-like puddle at "The Narrows" on the North Umpqua River, trying hard not to get eaten by the many caddisfly larvae that hung out in the same puddle.

It looks like a damselfly larvae wearing a fat suit.

Yeah, the wide bits in back make it unique. But I think I've figured it out: Timpanoga hecuba, a "spiny crawler mayfly."