Spiders live in houses all year round, but they are more active, and more visible in winter because heating systems keep houses warmer for longer, so the spiders are more active, and more mobile than during the summer. Just because flies are not around, spiders are quite happy to exist on a diet of other insects and grubs which they can find around an average house, but whch the occupiers don't normally see. Because spiders are on their travels more frequently, their tendency to appear in baths and basins also increases - not due to the popular myth that they climb up plugholes, apart from the impossible negotiation of the U-bend, spiders are much to fastidious to go messing around drains, it's because having wandered into a bath or basin, they are unable to get out, and remain in place until liberated. If you don't like to get involved, drape a towel over the edne of the bath and let it rech the bottom, the spider will probably be gone by the next day.