What thorny said! And yeah, ants generally are not a problem, but some of their livestock can be. Ants actually herd, protect and ‘milk’ some kinds of aphids, leaf hoppers and other sapsucking insects, which eat the sap of your plants and produce a sweet substance called honeydew which ants like. Honeydew plus leaf damage also opens a path for fungal diseases, which further damage the plants. And please don’t spray at least until you know what the problem is, because that will also kill ladybirds and lacewings who eat a lot of pests, as well as killing bees. And if you water in the evening, water the roots rather than the leaves, however nice the watered leaves smell!