Looks like it is probably the squash bug nymph. Be certain to check for eggs under the leaves and scrape those off to avoid a plague of these nymphs when they hatch. I got so tired of flicking them in water I grabbed a tool and just started squashing them.

I totally understand yer frustration!

Thank you, chicken coop. I'll check it out again this evening.

My favorite way to catch a lot of squash bug nymphs (or leaf-footed bug nymphs or stink bug nymphs) in a hurry is to use a link roller. Roll it right over them, placing one hand beneath the leaf to support it and quickly rolling over the bugs with the lint roller. They'll stick to it and you can pull that layer of paper off the lint roller, wad it up and through it away. You won't get all of them at once, but you can catch a lot of them. You also can use duct tape in a similar way, and both duct tape and lint rollers also can be used to remove squash bug eggs from the undersides of the leaves. It is important to catch them while they are young because they are a lot harder to kill when they are older.

I can't tell if they're SBNs or cabbage aphids!

And do be sure to keep an eye out for the adults. They are especially easy to kill while they are linked together mating, but you want to catch and squish every one you see. A good time to check is early morning and late evening. By killing the adults you prevent egglaying and hatching. If you do a search of 'squash bugs' you can find some pics online, I'm sure.