fungus gnats?

what are they and how do you control them. Now that I've got shelves and lights set up inside, and a greenhouse outside, I remembered reading "something" about them...and want to prevent them. So far haven't seen any critters (other than a butterfly caterpillar that snuck in with some passi cuttings) but want to be prepared..

They are tiny black gnats that lay their eggs in soil. Once the eggs hatch, the larvae feed on decaying matter in the soil and on seedlings' roots. They can kill a bunch of seedlings in short order. (They do not harm mature plants.) Indoors, the adult gnats can be an annoyance as they buzz about your plants.

To prevent them, you can sterilize your potting mix either by microwaving it or cooking it on low in the oven for about an hour. This kills pathogens, fungus or gnat eggs that might be in the mix. If you already have them, you can kill the larvae by using a product called Gnatrol (expensive) or by soaking mosquito dunks, which have the same ingredient, in water and then using that to water your seedlings. -Mosquito dunks are much cheaper than Gnatrol, so I always go that route.

Here's an interesting article, complete with pictures

http://www.omafra.gov.on.ca/english/crops/facts/06-079.htm#fsix

I got fungus gnats for the 1st time last year. Bt for Mosquitos will also work on fungus gnats. Downside was that I had to apply it as a drench, and drying the soil out is also recommended for fungus gnats. Bt is not an immediate quick kill, since it works on the eggs/larva stage - it may be 2-3 days before the adults start to drop off and you know whether or not it worked.

Also a possibility is those yellow sticky things used to catch other sorts of flying insects. One in each pot might help a bit while the bt is at work.

If your plants are mature enough and can take it, allowing the surface to dry out for a few days can also slow them down a bit. May not work with plants that require constantly moist soil; but it would work with snake plant.

I couldn't find the bright-yellow sticky traps without ordering them, so I picked up some fly paper. When I opened it, I was worried that it wouldn't work because it isn't bright yellow. But I hung it, and within a few days only a few gnats were left buzzing around. It's unattractive, but it does work.