Okay, I think I found out what they are. I was initially thrown because most sources say that they are any color except black, and my little buggies are definitely black.
One name for them is Snow Flea (although they're not fleas at all and do not bite), and another is Springtail. They have tails that are carried under their bodies and can be triggered to spring them up to 77 mm according to one source. This would explain why I've found a few on my walls!
They are more abundant when things are very moist in worm bins, and less so when they dry out a bit. I've never seen more than a few in mine, but as we all know, when you see a few of something, most likely, there are many more.
The biggest threat it seems is that they will eat the food meant for the wormies! They may also feed on very weak or dead worms, but that's a helpful thing, right?
Anyway, I'll keep my eyes open to be sure that things dry out a bit, but not too much so. Meanwhile, here are a couple of pictures I pulled off the Internet in case they might be helpful to anyone.
