hmm ants do eat the larval stage of many insects, these ants i would welcome, if the ants are aphid milkers id worry about aphids. If they are a bother rather than using poision, try Tangle Foot, this product goes at the base of the stem and they cant climb over it. if your plants touch the fence however, this wouldnt work. if the ants are eating the plant, there are products like antex, or products that they take to the queen and wipe out the whole colony. there is a good chance they are a benefit to your girls though and poisions are poision
peace