I used to try to get rid of ants until I saw how beneficial they can be. I had a bed of digitalis which had been attacked by aphids. I was amazed to see a line of ants marching up the stems, each ant collected an aphid and took it back to its ant's nest. They cleared my pest problem in no time. This let-things-lie policy, however, is purely a personal choice.

This link may help:
http://www.ipm.iastate.edu/ipm/hortnews/1998/6-19-1998/antsinlawns.html

I used to let ants be, and they actually ruined sizable sections of my lawn by over-cultivating the soil (allowing it to dry and killing the grass) and mounding it. They are my worst lawn pest.

If you're ok with synthetic insecticides, I have killed ants successfully with Triazicide (both granular and liquid), but I don't know if it's labeled for tomatoes. It has not had the effect of killing my earthworms, either. If not labeled for your use, check the labels on malathion or Sevin (both of which will knock ants out and are labeled for use on many vegetables/fruits).

While the ants I had in my previous residences were not a problem, in my experience here, ants are not beneficial and knock-down is a must.

I would suggest shaking the Triazicide granules in the area where the ants are (as well as some surrounding area) and watering it in before you cover it up. It is nonsystemic, and therefore shouldn't create any issue for your tomatoes.

You cannot use that product in vegetable gardens. And Sevin is one of the chemicals most harmful to earthworms and Triazicide does damage their populations, as well. Truthfully, ants can effectively be controlled with granulated baits such as Spinosad (safe for gardens), Amdro, or the like. Ants take the product deep into the nest chambers where it is passed around to everybody, including the queen. A tiny bit of product does the job, with no problem for non-target organisms.

crumblepenny, I was struck by your observation that ants were taking aphids from digitalis plants back to their nest. I have never heard or read of this. Has anyone?
Ants routinely move aphids from plant to plant or from one part of a plant to another.

What can I say? I can only tell you what I saw. Why would they move them from one plant to another? Ants are highly intelligent creatures and this seems a waste of their time to me. I don't doubt what you have said - I'm just curious.

I've read about ants tending to aphid EGGS in their nests, but not live aphids. What would the aphids live on?

Ants will move aphids from location to location partly to avoid overcrowding and also to take advantage of juicier plant parts (according to the ants), shelter from the sun or rain, etc. Hardly a waste of their time, but just the opposit.

Perhaps they were eating the aphids - who knows. Thanks for the other info. It's always interesting to know these things.

Ants herd/farm aphids to protect them (the aphids) from predators. The ants eat/collect honey dew, which is the byproduct of the aphids' feeding on your plants...it's basically aphid poo/excretia.
The ants will protect the aphids from their natural predators, the aphids will gather in large numbers on your plants, sucking the juices, producing poo/honey dew which in turn can lead to the developement of sooty mold.....and that lovely black stuff, if left long enough, can smother your plants. If it is thick enough, it will prevent your plants from taking in nutrients, air, light, water etc., through their foliage. The plant will die. That's only in severe aphid infestations, of course. But the ants play their part by keeping predators away from the aphids....it's best to get the ants out of your garden.

RENEE

Thanks for that. Coincidently, I've just been given the May issue of National Geographic and in it there's a very interesting aticle about the inch-long Bulldog Ant (native to Australia). Nothing to do with this conversation I know, but still very interesting.

The most interesting article on ants I found was in the 'National Geographic' of June 1984 pp 774-813. The illustrations are superb.