Ants on plants are usually after aphids or the "honeydew" that scale insects and aphids produce. They are not usually eating the plants themselves.

Get rid of the ants if possible.They are trouble and spread disease easily.Like Buy O said they must be attracted to something.Perhaps a honeydew from aphids or something else.I tried peppers in my greenhouse last summer , but no more because it got to many aphids ( I grow organically So nothing gets sprayed )My peppers are outside this year. You can try sticky tape put or a powder that is safe but not as effective.Garden shops can help you out.If you don't grow organic you have more choices and very effective ones.

Thanks so much for the info! I looked at the bottoms of the leaves, and sure enough, many aphids. I sprayed some insecticidal soap for now but I'm thinking I may use something stronger (not opposed to pesticides myself).

Tnanks again

Some ants tend or farm aphids, even carrying them into their nests in the ground for the winter, bringing them back out in spring.

At least they're not in your pants.

This is probably just a coincidence ... but Farmers Almanac said putting rosemary clippings in windowsill will keep ants out. Ants on my trumpet vine drive me crazy every year. Two weeks ago, while pruning some rosemary, I remembered that. So, I dumped the clippings around the base of the vine. Next day - no ants. Still no ants. Maybe they'll be back tomorrow. I'm just sayin' ..... !