Some kind of mite found on several cacti in an indoor garden. The one in the picture is a small Melocactus. Its spines are 4-6mm long, so the mites are a fraction of a millimeter long.

They look similar to spider mites, but smaller and with no visible webs. I believe they caused the scarring visible on the lower part of the cactus, and there was similar scarring on the other plants I found these on.

About 5mm long. Found inside the center leaves of a Kalanchoe luciae. I couldn't tell if it was feeding on the plant or just hiding out there. I'm fairly sure the white powdery substance is farina from the plant that rubbed off onto the insect.

If it's not apparent from the pictures, it has 6 legs, (I think) 11 abdominal segments, fine bristles along the length of its body, and a "tail" consisting of around 40 longer hairs.