[Oops, I hadn’t meant to send this yet, but I hit publish by mistake!]
I’ve never heard of sawflies, and now I have seen two different ones, and the larva (caterpillar) of another. Just plain luck. (I do realize some of you probably think I am a little eccentric to get excited about a fly.)
Sawflies are in the order Hymenoptera together with ants, bees, and wasps. All of these insects have two pairs of wings, unlike true flies, Diptera, which only have one pair of wings. You can clearly see the four wings in this photo. So they aren’t actually flies at all. They have a saw-shaped ovipositor, hence the first part of their name, but they are nearly all harmless plant eaters.
They have a life cycle with four stages, eggs, larva, pupa, and adult, and the adults only live for about 8 days, which maybe why I haven’t often seen them! These next two photos show the larva of the North Americans Sawfly in the photo above:
Here are the larva and the adult of one called, I think, Monostegia abdominalis.
The larva often congregate in large groups to feed, and rear up when startled. I’m not sure which species this is, but they are sawflies, not caterpillars, because they have a pair of prolegs on every segment, and no claws on the prolegs: