Ant colony in my compost bin: are they beneficial?

Question

I've got a smallish black plastic compost bin in my garden and I recently noticed that an ant colony has taken up residence. This has happened a couple of times in the past, but they tend to move on when I turn the compost (not surprising, given I'm ruining their home).

However, is their presence actually good for the compost? Do they speed up the composting process by aerating it and dining on the 'food' therein? And if so, should I leave them be for a while?

The ants themselves don't bother me.

Answer 1

The composting process depends on a complex chain of organisms -- which can include ants -- to consume and thus break down the food in your compost pile. See this page from the University of Illinois extension service, which comments on ants in compost:

Ants - Ants feed on a variety of materials including fungi, seeds, sweets and other insects. They help the composting process by bringing fungi and other organisms into their nests. Ants can make compost richer in phosphorus and potassium by moving minerals around as they work.

Since the ants don't bother you, letting them work on your compost a bit would have some benefit -- you're enhancing the food web by allowing them to stay. The downside is that, by not turning the bin when the internal temperature drops, you may not achieve high enough temps for long enough to kill off weeds and harmful bacteria. But if your mix wasn't going to achieve this anyway, then it's not an issue.

See also the following diagram of the compost food web, taken from this chapter on composting:

_{(source: fao.org)}

Answer 2

Ants in compost heaps usually means the heap's too dry. The absence of obvious brandlings and other worms should confirm that. Add water and continue turning it.

Answer 3

Agreeing with @bstpierre but as I find they are usually a pest (bites,etc) I put ant powder on them. There's always a tinge of regret and I try to use a minimal amount of powder because that stuff also kills all the other bugs and insects that live in compost. I need a more selective alternative but I suspect there isn't one. luckily we haven't had ants in our barrel for a while.

Answer 4

Putting poison in your compost is crazy. If you feel really strongly about not having ants, then just cut off their access to your compost: put the compost bin on feet that rest in containers of water. Then just have patience and nature will take care of the rest. Eventually they'll go away; either another insect will eat them or they'll run out of food, but at some point Pachamama always takes care of things.

Answer 5

What possible harm could the presence of ants bring to your dirt? I am thrilled when I see bugs in my compost, it means that it is a healthy ecosystem and bodes well for the plants.