Spiders in homes during late August are driven by mating cycles

The seasonal appearance of large spiders in homes during late August and September is driven by biological mating cycles rather than a search for warmth due to dropping temperatures. While it is a common misconception that spiders enter houses to escape the cold, the actual cause is the maturation of male spiders.

According to the Office Pour les Insectes et leur Environnement (OPIE), the spiders most frequently encountered in French households are domestic species such as Eratigena duellica and Tegenaria domestica. These spiders are considered harmless to humans, as their venom has no known medical impact and they rarely pierce human skin.

During this period, which typically lasts from late August until mid-October, male spiders reach sexual maturity and leave their hiding places to search for females using pheromones. The females generally remain stationary within their webs. This movement of males across floors and through rooms creates the illusion of an invasion, though the spiders have often lived discreetly within the home for much of the year.