Spiders are an important part of California’s diverse ecosystems, helping control insect populations. With over 600 documented species, California’s varied landscapes, from deserts to coastlines, provide numerous habitats where spiders thrive.
Defining California’s Spider Season
While there isn’t an official “spider season,” California sees increased spider activity and visibility from late summer through fall, peaking around September and October. Warmer Southern California regions may experience extended activity, sometimes into winter, due to the mild climate.
Changing temperatures and humidity levels significantly influence spider behavior. As summer progresses and temperatures remain warm, many spiders reach maturity. The subsequent cooling temperatures in fall often prompt spiders to seek more stable and sheltered environments, sometimes leading them indoors. Additionally, periods of increased rainfall can contribute to a larger spider population by supporting more vegetation and, consequently, more insect prey.
Why Spiders Become More Visible
Spiders become more visible in late summer and fall due to several biological and environmental factors. A primary reason is the maturation cycle; many spider species reach adulthood by this time. As they grow larger, they become more conspicuous and their webs, especially those of orb weavers, become more noticeable.
The onset of the mating season is another significant factor. Male spiders, having matured, actively venture out from their hiding spots in search of females. This increased movement makes them more likely to be seen by humans, both outdoors and sometimes inside homes. Female spiders, while often less mobile, attract males through pheromones, indicating their readiness to reproduce and lay eggs.
The abundance of insect prey during warmer months provides a plentiful food source, supporting larger spider populations. As outdoor temperatures drop and insect populations seek shelter, spiders may follow their food source indoors. This combination of factors makes them particularly visible during California’s “spider season.”
Common Spiders You Might Encounter
Orb Weavers
Orb weavers, known for their large, intricate circular webs, are often seen outdoors in gardens, between trees, and near structures. Species like the yellow garden spider grow considerably by fall, making their presence more apparent. Orb weavers are generally harmless to humans.
Common House Spiders
Common house spiders are often found inside homes, building irregular webs in corners, basements, and garages. While they can bite if threatened, their bites usually result in only minor irritation.
Wolf Spiders
Wolf spiders, robust and hairy, are ground-dwelling hunters that may wander indoors, particularly into basements or crawlspaces. They are not considered highly venomous to humans.
Black Widows and Recluse Spiders
Black widow spiders, recognizable by their shiny black bodies and a distinct red hourglass marking on their abdomen, are also active during these months. They prefer dark, secluded areas such as woodpiles, sheds, and garages, and their venom can be medically significant. While often mistaken for brown recluse spiders, the brown recluse is not established in California. Instead, the desert recluse is the most common recluse spider found in the state’s arid regions, and can deliver a necrotic bite.