Any question answered...

I've got a couple of spider plants in my room that a friend of my girlfriend's was looking after over summer, and very nearly killed.

They're starting to look healthy again, but seem to have been colonised by a load of tiny black flies. Is there any way of getting rid of them, without introducing another species to my bedroom, and without harming the plants or the air quality in my room?
Spray on a very dilute solution of washing up liquid.