I think you might be seeing some which have swarmed, the queens and males have been emerging here recently and you usually see a lot of workers running around too. Ants do like hot weather, not that it is hot now but they will nest in sheltered places such as greenhouses and under stones or slabs.
They usually only come into houses when there's food they like, such as sugar or honey which they can detect. I have a neighbour who used the squeezy bottles of honey and obviously wasn't careful enough about keeping it inside the bottle, she had ants every year and used to place Ant powder (poison) for them to take back to the nest. Far better to leaves the ants and clean up the honey!
Janet
