The greenest way is to squish them with your fingers, but that won't get rid of them since they are nesting in your garden.
I love these questions, and they do come up regularly. They sort of amount to "How can we kill bugs without poisoning ourselves and the planet?" which is a tough question, given that no matter what you use, you are still killing.
- The most "sustainable" thing to do would be to learn to live in harmony with the bugs and/or
- find a natural predator for them; thus we release ladybugs to reduce aphid infestations in the garden.
Finding a natural predator
So perhaps the most sustainable approach is to release some creatures that eat ants in your home? What eats ants (besides anteaters)? Spiders, lizards, birds, etc., says the crew at Answers.com,but I don't imagine anyone really wants those critters running around their house either.
The important distinction here is how we can eliminate ants from the home with the least impact to the ecosystem (including our dogs).
Ant traps, and other suggestions from UC Davis
UC Davis has several recommendations for managing ants with minimal environmental impact.
First they point out that it will be almost impossible to get rid of ants on your property altogether, nor would you want to, since they do provide a link in the food chain.
- They suggest that humans caulk cracks heavily, in kitchens in particular,
- that we seal sugars and other food sources well,
- keep garbage far from the kitchen,
- clean up all spills thoroughly,
- and finally they suggest using "ant traps," which are actually bait systems.
Ant traps are containers that allow worker ants to come in and bring back poisoned food to the hive, which kills all of the invading colony.
I have had a lot of success with this approach, and as long as I put the bait/traps in tight spaces where the dogs can't reach them (preferably near the doors, where ants tend to enter and I can't caulk), there is no issue.
For more information:
Read "I have bull ants, fire ants, and tiny black ants. Is there a green and effective way to get rid of these pests?" a Q&A answered by Richard Heller.