I love in a townhouse and these guys (and bigger and redder ones) regularly pop up. They come into my bathroom, and are harmless. I just pop them back out the window. Most are herbivores and eat decaying plant matter, but some eat insects. I would check for damp and check if the wooden windows are rotting, as that could possibly be a food source for the herbivores.... I am no expert though! They are completely harmless and cannot bite you or anything, but like silverfish and wood lice, can point to a more serious issue. I have slugs living under my kitchen sink unit and feed them cat food when they pop out at night! All these seem to like damp conditions, so I would look into that if I were you. If using slug pellets, please be careful of any domestic pets and wild birds, as they are lethal to them too. Dispose of any dead slugs and snails carefully so as not to poison thrushes and other birds.