Sounds like they might be pavement ants, who like to like in...concrete, of course. We've had them around our house's foundation. They're pretty harmless as long as they're not establishing themselves inside, and treating them outside always seemed kind of futile to me---I mean, we have lots of concrete around the house for them to love.
They won't harm your plants.
"My predominant feeling is one of gratitude. I have loved and been loved;I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal, on this beautiful planet, and that in itself has been an enormous privilege and an adventure." O. Sacks