On 10/01/2012 21:34, darronb wrote:

Since are central heating came on we have been infested with extremely
small black flies. I had noticed them coming out of a cactus plants
soil, and as much as I didn't want to was forced to move the plant
outside. Now we have flies coming out of other plant pots inside the
house.

My question is what are they exactly and what can I do to get rid of
them. Hopefully without losing my plants.

As the other replies have stated, these are sciarid flies. Don't bother
with pesticides - in my experience sciarid flies are resistant to them.
The yellow sticky sheets are effective, but will not deal with all the
flies. And if one gets through to lay eggs, you will have dozens more
to deal with.

They need damp compost to survive, so dry soil will eventually see them
die out. In any case, unless your cacti are of the christmas cactus
type, they shouldn't be watered at this time of year. They should be
left in a cool, well-lit window and kept completely dry until April. It
is best to not close the curtains with the cacti on the glass side, as
although many are frost-resistant if completely dry, some aren't, and a
severe frost might see the temperature fall enough to damage them.

--

Jeff