If you have a fly problem of any kind that can be traced back to your compost bin that means your compost is too wet. These vermin need a pretty moist environment for the eggs to hatch and that larva to grow and develop into the adults. You can add add a dessicant to the mix that will help temporarily, but getting the moisture level down is what is needed.
Most likley you don't have "fruit flies" but instead "fungus gnats", similar enough that many people assume they are the same.

I suspect that you are right. I've been lax in adding brown stuff, so it's mostly greens. I've been adding lots of shredded paper now, so hopefully that will help. In the meantime, what's a dessicant?

As an emergency measure, if you have clouds of the bugs, you might invest in a bottle of Rotenone/Pyrethrin spray, which would very likely be available at any nursery that stocks organic stuff, and spray the top of the bin every now and again to knock out the adults.

Also works pretty well to get any garden pests.

Here is a link that might be useful: organic bug spray

Mixing in dry browns is a good measure. A layer of them on top may seal the deal.

Agree with Pablo. Anytime I got them, I quickly got rid of them (in a day or less) by putting a layer of dry leaves on top. Newspaper or shredded paper would work just as well.

Never, ever use pyrethrin sprays or dusts on your compost pile. Rotenone was determined to be a much too toxic pesticide for general use years ago and is not longer recommended except as a very last resort.

"Never, ever use pyrethrin sprays or dusts on your compost pile. Rotenone was determined to be a much too toxic pesticide for general use years ago and is not longer recommended except as a very last resort."

Could you please better inform me? I use a pyrethrin based organic spray all the time on aphids and flea beetles.

Pyrehtrins are broad spectrum poisons that will kill what ever they contact, beneficial as well as pests and should not be used except as a last resort.
Controlling aphids seldom needs anything stronger than a sharp water spray, repeated as necessary. Flea beetles I have not seen since my soil has gotten to be well balanced, but I am told for those with them floating row covers work well.

Dessicant is basically anything that absorbs water. When you buy electronics you'll get a little pouch with some salt like crystals in it that says "Don't eat", thats dessicant. It keeps water from condensing in the box while the electronics are shipped.
In your case shredded paper should make a fine dessicant.

Don't get thinking fruit flies appear from fruit... I can't think of the term but it was a long time ago that people discovered rotting meat attracts flies it doesn't create them. The flies came from some other place to your bin because you'd created a breeding ground for them. Then they breed very quickly so it might seem like they "just appeared".

Spontaneous generation?

Some fruit will have fruit fly eggs on it when you get it. Think about that next time you don't wash food :)

Ahh theres a one word term for it that eludes me. I can still picture the highschool text book with 2 slabs of meat one covered and one not and the uncovered one having flies on it...
Strange one you remember eh?

The pyrethrin chrysanthemums grow on the higher slopes in the mountains of Kenya, beautiful fields of white flowers. The plants are processed for the pesticide, which breaks down within a matter of hours when exposed to sunlight or oxygen. The plant residue, after extracting the majority of the pyrethrin, is then used to make mosquito coils that people burn in their houses to ward off mosquitos. It is the common ingredient in insecticidal soap. This soap is useful on aphids, particularly on tiny, delicate seedlings.

From wikipedia, my underlines:
"The pyrethrins are contained in the seed cases of the perennial plant pyrethrum (Chrysanthemum cinerariaefolium), which is grown commercially to supply the insecticide. Pyrethrins are neurotoxins that attack the nervous systems of all insects. When present in amounts not fatal to insects, they still appear to have an insect repellent effect. They are harmful to fish, but are far less toxic to mammals and birds than many synthetic insecticides. They are non-persistent, being biodegradable, and also break down easily on exposure to light or oxygen. They are considered to be amongst the safest insecticides for use around food. For humans, pyrethrin is known to irritate eyes, skin, and respiratory systems. It is particularly harmful to aquatic life."

It is useless against white flies.

Here is a link that might be useful: made from flowers

Phlogiston is the mythical ether that was supposed to carry the force of life. Pasteur used those weird flasks etc. and cheesescloth over jars to disprove it.

Parthenogenesis is arising fully formed, but that happens.

Abiogenesis, similar to spontaneous generation is life coming from non-life. This can have the false implication of something spontaneously generating- or it can refer to the theory that life came from chemicals/electricity etc. in a primal soup in the early days of the planet.

Ya, I'm a science geek.

Parthenogenesis is what I was thinking of, thanks!