The opposite is true in the case of aphids, which are pretty serious destroyers of crop-yielding plants. Some ants farm aphids for their honeydew. Rather than

The opposite is true in the case of aphids, which are pretty serious destroyers of crop-yielding plants. Some ants farm aphids for their honeydew. Rather than destroying them, they encourage their population on the growing-tips of plants. If you introduce aphid-eating insects, such as ladybirds or lacewings, the ants will fight off the attackers.