A lot depends on the species you are talking about. Leaf cutter ants will damage plants, Carpenter ants will feed on your house frame, Fire ants will bite you.

I don't think your wall is the appropriate place for an ant nest. As you are witnessing, they will only multiply. They are just too close for comfort. Do you want ants getting into your cupboards, crawling over you while you sleep? In your sugar bowl? Ants in your pants? Get rid of them before they get rid of you.

I have several ants nests around my garden and in walls and they don't seem to do any harm. I don't think we have any of those ants in the UK Bathgate, our biggest is the wood ant and they have a nasty sting but their habitat is woodland.

Taz, is this a separate double wall, is one of the walls your house wall? If the latter, Bathgate's concern about them moving in with you is well founded. Otherwise, ants are beneficial to a slight nuisance in the garden, and sometimes cause drought damage when they move into pots.

Their habitat is a breeding ground for fungus and bacterial growth.

The whole world is totally infested with ants. Place some ant baits in the areas you mentioned for local control.

True, Bathgate, though primarily bacteria and fungi beneficial to the ants.
True, Loosestrife, few ant species, at least in our gardens, could be considered endangered.
I also did forget the best reason for controlling ants. Some species encourage and protect members of the aphid family (and some caterpillars) to harvest their honeydew. If you are having trouble with blackfly, greenfly, scale, or mealybugs, watch the ants--you may need to kill them first, before managing the sucking pests.

Loosestrife I think your statement that "The whole world is totally infested with ants" is a little over the top! Frankly the whole world is "Infested with humans" Ants are a natural part of nature unlike ourselves and, unless they appear to be causing a problem I'd recommend a live and let live policy!

I heard they don't like chalk. Apparently they will not cross a line of chalk. Never tried though. I have some ants that go up and down my tree and have been doing for years. To date, they haven't bothered anything in my garden. But they do worry me being there.

Don't forget you guys Tugbrethil, Bathgate and Loosestrife, you live in the USA where ants are a big problem (so I believe) but it's not the same in the UK where they don't tend to eat our buildings.

They persistently nested in a trough until because of all the root disturbance one heuchera is no more....
I'm thankful they're english ants...

Your right Moon. I should have used the word populated. What I meant was their numbers are astronomical and they occupy just about every ecological niche conceivable. Their habits are fascinating and there are quite a few recorded lectures about their habits to be found on the web. I included in my comment the phrase that Taz used " totaly infested" as an attempt at literary continuity that's all and nothing more. WOW! Believe it or not, a flying ant just landed on my hand.

The ants are not a concern in terms of damaging your house or biting you badly (although they can and do nip a bit if you disturb the nest and remain nearby), as thankfully, we're in the UK - but its entirely possible they will destroy roots of your plants. They only do this to enlarge their nest, and unfortunately, you've obviously created the perfect place for nests to be built - warm walls with friable, dryish soil that's freedraining inbetween.

Ants don't like wet conditions, so you could make sure you water the bed frequently, that would help discourage them, but for major nests, quite honestly, the simplest and least damaging (ecologically) method of dealing with them is to boil a kettle, open up the nest and pour boiling water into it, then run like the clappers before the soldiers appear. This won't do your plant roots much good though, so probably best to stick with puffing ant powder liberally into the heart of the nest once you've opened it up a bit. Best done when you're wearing boots and gloves... the soldier ants will come out and they're the ones that attack... They won't kill you, but lots of little soldier ants biting your toes isn't a great way to spend ten minutes...

Oh dear the boiling water is so cruel to me, as I've got older I tend to let nature alone as much as possible.

I know Cammomile - but if the wall becomes completely occupied by ant's nests, then no plants will survive... keeping it damp is the kindest option.

Many years ago I had a very unpleasant experience with flying ants from the low walls that used to front local properties. That year was a bumper year for the horrid things when they swarmed in their thousands so now if I find ants nesting in wall edgings, patio slabs or under plants I sprinkle ant powder. I'm afraid it's them or me and I'm bigger than they are! And more terrified.

Its the biting red ants I dislike, they inject formic acid which is so very painful
a paste of bicarb can ease it......its bicarb for bees too
oh and vinager for wasp stings.......

when we're all gone ants will rule the world......?????

Hmm, not sure about that Pamg - it'll be cockroaches, ivy, fungii then ants and termites...;-))

Giant insects and Triffids then....
.Or have I seen too much Dr Who ?

The way the human race carries on, it'll be sooner rather than later!

Yes, its depressing isn't it, human nature never really seems to change much in terms of improvement...

Thanks to everyone, I am still not sure what to do. The thought of killing them still does not sit well with me, we as humans tend to destroy what we don,t like or want with out a second thought. At the moment they are not a problem, just got to be careful when weeding. By the way the wall is not attached to the house, and no I have no green or black fly in the garden. May try watering to discourage them rather the kill them.

Watering more 'should' deter them...

thanks, the wall works like a huge trough and soon becomes dry, so hopefully I will remember to water more often.

Try mixing some gel crystals with the soil - helps to retain the moisture very well. I use them a lot in our dry places.
We have huge numbers of ants here but they don't seem to do any damage - the only unpleasantness is if you disturb a nest and they come out running, and the particular day in August when the wedding flight takes place - but that's soon over.

Taking into account some of the broader comments made above( including mine), for those interested in the subject of the human race vs. insects may I suggest viewing an interesting documentary film made some years ago titled " The Hellstrom Chronicle".

Organic ant management tools: ground up orange peel, spearmint, diatomaceous earth, and ant bait with spinosad.

Spinosad's what's in ant powder, Tugbrethil - don't think its available here in any other form.

Also sprays and baits here, Bamboo. Ant powder here is mostly one of the "'thrins"--i.e. permethrin, deltamethrin, etc. I wasn't sure of spinosad's availability in the UK.

Oil of lavender is good for bites and grazes of all kind. Stops itching and even bleeding in minor cuts.

Once again thanks to everyone, there are some good ideas among the answers. I will not be killing them, will try to discourage more nests, so a few of your ideas will be put to use,