Little black nats flying around?

[greenpassion]

I have recently gotten into moss terrariums, using clear glass vases, and the moss is from my woods here in VT. These are situated on and under a glass shelf that holds my orchids of several varieties, all in S/H. Thus far I've never had these "fungus knats' before, and I think I've inadvertently introduced them to the area via the moss. Will these hurt my orchids? And how do I get rid of them, without if possible, getting rid of my little moss terrariums?