Just did some research on the net. Velvet mite larvae have six legs and feed on blood from spiders, etc, and occasionally from humans! The adults (eight legs) feed on vegetable matter and garden debris. Sometimes called harvest mites, they can attach to the skin of animals and bite them. They live in garden and woodland debris. Red spider mites are much more common and damage plants, but are only red in autumn. They lay their eggs on the underside of leaves.
I know nothing - this is just a bit of research. But it looks as though they don't nest in the ground and create heaps of soil.
