I think they move to the compost bins when the ground gets too wet (just like they move to pots) and if the compost is warmer than the ground but not too hot for them. The easiest solution I can think of is to really soak the compost and keep it wet, they'll move the nest. I've had that work with potted plants before.

My husband uses a orange oil mixture to kill fire ants. He makes a mixture of 1 part orange oil, 1 part molasses, and one part compost tea or just water, then uses about a cup full with a gallon of water and soaks the mound. He also puts out benificial nematodes around April from the feed store. You mix these in water, and spray with your yard sprayer, they also eat fleas, and grubs. Barbra

Keep turning the pile, add green materials to raise the temp and like tx_ag said soak it down.

The main thing is if you get the temp of the pile up, the ants will go away.

I had the same problem this weekend, as the OP, and no idea how to handle it, so I guess I will keep it extra moist.
Barbra,I've heard of using that orange oil mixture on mounds, but I would be concerned if it would also kill worms and other beneficial insects who are also in the compost bin.

Two different falls I had fire ants in some plants before bringing them in. Someone on GardenWeb suggested sprinkling white sugar on top of the soil. I did and they were gone... soon! Not sure if they ate the sugar and died or it drove them somewhere else. Maybe that would work on compost?

Gosh, I never thought about that. My husband uses it for mounds, its organic and works so well. We do not have a compost pile. I would ask this question to Bob Webster Sunday morning on his talk show. I think its channel am 55. He covers all of Texas, we listen to him on our three hour drive back from the coast on Sunday. Barbra

Hey I think that was Bob Webster I saw at Fannick's nursery morning the last time I was there in Fall on a Sunday morning....he was broadcasting. Too bad I didn't have the question then.

Thanks for all the tips. I'm going to finish pulling out everything on bottom of the pile where the ants are the worst and deal with that batch separately. Whats' left of the compost I will keep moist and turn A LOT. Hopefully that'll prevent them from re-establishing the colony.

Looking at this compost bin, it is a lot drier than the other.

Re: more "green" - do you mean more vegetable matter as opposed to leaves?

Fannick's is my favorite nursery in San Antonio. We have such good luck with their plants. Bob is always pitching the nursery, but he actually owns Shades of Green Nursery in San Antonio. Barbra

I tried the sugar on the ant bed by my compost pile last fall and they just laughed at me. I've tried the molasses & orange oil mix on ant beds in the yard and it brought the earthworms to the surface, so I don't think they like it.

He owns Shades of Green? Interesting! I confess I don't like SoG as much. It's very nice but a bit boutique-y, know what I mean? Fannicks feels more like a get-dirty-and-garden kind of place. SoG just feels like a put-out-pretty-pots kind of place (fitting for its location) and i'm definitely a get-dirty kind of gardener. :) I like Rainbow Gardens as well, and it's better labeled than Fannick's, but Fannick's is closer to home and they know me now.

Anyway, thanks for all the suggestions. Hopefully I can salvage this pile and avoid it next time.

On a related note, in clearing out my garden beds, I dumped a big pile of dirt from them on the ground, which my toddler immediately dove into. At first I laughed. Then I saw fire ants had gotten to the beds as well (since the freeze, I hadn't touched them). Fortunately, I pulled my kid away before the fire ants found him, but he couldn't understand why he couldn't play in this wonderful big pile of loose dirt, aka Heaven.

Thanks Barbra, let us know what he says, and if he has any other suggestions for compost piles.
Susan