Thank you both for the prompt replies! I must apologize; the photos I posted here were only for identification of the cactus, not the critters who've attacked it. I tried to get photos of those but they were not very good. I was too close, then it rained and I came inside. I'll post what I have if I can clean up the images a bit.
My guess that they are red spider mites came from a photo I found online.
There were never webs on the plant. There was a strange, lumpy mass of dried brown "goo" near where I first saw the things. There had been 3 flower buds that they've managed to destroy already. Since the buds fell off, they seem to be wandering all along the plant, and several have disappeared this morning. They appear to be more red/orange than they appear in the photos
Ah, got a couple photos: That's the little bugger!
