Hi, I'm new to this group.

I have a conservatory attached to my house with about 60 orchids. Over
the past year or so, I've noticed bunches of tiny black dots - smaller
than a pinhead - that cluster on the ledges and walls. The largest
concentration is on the wall opposite where my plants are. I *do* have
a few plants that have tiny black spots on the leaves, but the spots
are flush with the leaves unlike these things. Can anyone tell me what
these may be and how I can get rid of them? I did a massive cleanup,
but they reappeared 2-3 weeks later...

Many thanks,
Laura