It's hard to see enough detail to ID the insect with certainty (we realize it's hard to get a good photo of something so small), but our best guess based on where you are seeing them and their overall size and appearance is that they are dark-winged fungus gnats. They are very common nuisance pests around houseplants, as the larvae feed on fungal spores and other material in the organic matter of potting mix. One key way to discourage them is to not over-water plants, letting the potting mix get somewhat dry (at least an inch or two deep into the container, depending on pot size and the tolerances of the plant) so the larvae are less likely to survive. Make sure that any saucers used to catch drips under pots are emptied promptly after watering, so the collected water doesn't sit in contact with the drain holes and seep back into the pot, which could drown roots and support fungus gnat larvae.

Yellow sticky traps (essentially just vibrant yellow index cards coated in adhesive) can be used to help monitor where they might be concentrated most, though it won't catch all of the population. Treating the potting mix with Bti, as noted in the page linked above, is a good way to control an outbreak. More than one treatment might be needed; follow product label directions for how to apply the granules and how often to re-apply. The adults are harmless in terms of bothering people or plants, but the larvae might consume some root tissue; references vary on how much they do or do not feed on roots compared to other materials in the soil. They aren't drawn to the water in the watering can the same way a mosquito would (to lay eggs), but they can be clumsy fliers and probably just fell in and drowned in the water.

Miri

Miri, that is so helpful, thanks a million for such a great reply!

 

John 

You're welcome!