Although the name "sawfly" suggests that these insects are flies, they are not. They actually belong to a suborder (Symphyta) of the Hymenoptera (includes bees, wasps and ants as well as sawflies). Their larvae look very much like moth or butterfly caterpillars, but the sawfly larvae have more prolegs.

They are called sawflies because, according to Steve Marshall, the females "have a sawlike ovipositor that flips down like a jackknife to saw into, and lay eggs in, leaf edges or stems."

Thanks to iNaturalist experts for help with many of the IDs of these difficult to identify creatures.