Ants in my greenhouse
Yes, they can cause problems. I've had them build nests in pots, they like dry conditions so they get in after winter when the compost is on the dry side. I now do frequent checks .Lift the pots up and if compost falls out the bottom it can indicate that ants have got in and displaced it. A good soaking can discourage them, or sprinkle ant poison granules under the pot and don't let a pot stand in the same place too long.
They can also farm aphids on plants but that is easier to spot than nests in pots.