Posted: 11/11/2015 at 08:48
This query has cropped several times before. This is what I have said then and have kept on file:
"There are two likely possibilities here. You may have fruit flies. They come from fruit but also live in houseplants. They especially like Yucca plants as they are very sweet. You can dispose of these naturally by filling a glass with vinegar and putting cling film over the top. Punch a small hole in the top of the plastic wrap and the fruit flies will go into the jar. Change the vinegar every week or until they are gone.
More likely, they are "dark-winged fungus gnats” (scientific name Sciaridae). These live in potted plant soil. They can be very hard to get rid of, depending on how many infested pots you've got. Nearly everyone who has potted plants has these flies in their homes but they sometimes become a nuisance.
Re-pot the plant completely with sterilised potting compost and spay the soil with BTi (available as 'Gnatrol' in the garden centre)"
I'm betting on the fungus gnats, myself.