The thrips I've seen were black (have gotten them a couple of times on
orchids, but mainly on gardenia bushes), and I needed my reading glasses to
see them.

It's hard to be definitive, but it sounds to me like the kind of
"decomposers" that run like crazy when you de-pot a plant that's overdue for
new medium. They almost look like lice. What are the plants in (what kind
of material)? Are they due for a change?

Diana