Stokes Croft has lots of Banksy graffiti

Had to ride through Stokes Croft today to the osteopath. Glorious day and my beetroot and pak choi seedlings are coming up in the allotment. The slugs and snails have been doing their worst and the black fly on broad beans and globe artichokes are being a pain. I keep finding ants nests - they seem to be the culprits as they move the aphids around to start new colonies. Squashing the aphids seems better than soapy water - anyone have any good ideas about getting rid of the ants on a 30 year old organic site with no access to electricity for boiling water and fires not allowed?