It is winter and cold outside and those pesky little bugs that you thought would be dead by now are now enjoying the warmth inside your home. What appears to be small Gnats are Fungus Gnats. Fungus Gnats are found in the soil of the house plants that you moved back inside your home for the winter or the soil that you purchased to repot plants. Fungus Gnats are about 1/16 to 1/8 inch long. They have light gray to clear wings and are poor fliers. They have slender legs and resemble small mosquitoes. Their antennae are longer than their head. They have a four part life cycle of egg, larva, pupa and adult. The adult is fairly easy to kill but the egg, larva and pupa stage are harder to control since they are hidden in the soil that your plant is growing in. Fungus Gnats can produce many generations in one year. The adult lives for 7 days and the eggs hatch in 4 days. Fungus Gnats feed on roots and organic matter in your house plant containers and you will always find them sitting in the soil, on the containers, foliage or flying around your house plant containers. 
Fungus Gnats caught on a sticky trap One of the biggest problems with Fungus Gnats is that they can feed on the tender roots of young seedlings. I am currently growing hostas from seed and have just discovered Fungus Gnats. The Gnats can feed on the roots, stunt the growth of the seedlings or kill the seedlings. The Fungus Gnats (not adult) were in the potting soil the I recently purchased.
There are several way to control Fungus Gnats in the home. Always allow good drainage and don't over water plants in your house for winter. There are several sprays on the market to control the adults. Make sure you read the warning labels of all insect sprays before using and make sure that Fungus Gnats is listed on the container. I have installed several sticky traps around my hosta seedlings and have caught many of the adult Fungus Gnats in flight (and have caught myself in the traps several times - they are sticky!) I am now using Bacillus thuringiensis (var. Israelensis) or "Bti " to kill the larva in the soil. Bti is a biological pesticide that contains naturally occurring bacteria that target and kill specific insects - in this case Fungus Gnats. The Bti is eaten by the larva and then they die. Bti does not harm animals, fish, birds, beneficial insects or humans. It does not contaminate the environment. Bti is hard to find in stores and nurseries. You may want to seek it out on the internet and have it shipped to you. Several application of Bti in the soil should rid you and your home of Fungus Gnats.
Happy Gardening!
The Creative Gardener