Around 40,000 spider species have been documented worldwide, and a small minority of these species are frequently encountered within homes and buildings. Some spiders that prefer to live outdoors often appear within structures due to accidentally wandering indoors or to pursue insect prey within homes and buildings. These occasional spider invaders include grass spiders, wolf spiders, fishing spiders, and even tarantulas. Other spiders that are frequently found indoors are synanthropic pests that have lost their ability to survive in the natural environment. The word “synanthropy” refers to organisms that benefit from living in close association with humans, and most synanthropic spiders spend their entire lives eating and reproducing within structures. Synanthropic spiders are often referred to as “house spiders,” and they include American house spiders, yellow sac spiders, cellar spiders, southern house spiders, and many cobweb weaving spiders. Unfortunately, the most dangerous spider species in the United States, the brown recluse spider, maintains a synanthropic habitat where they pose a medical threat.

Brown recluse spiders establish indoor harborages in dark spaces like closets, shoes, storage rooms, beneath clutter, attics, in piles of clothing, and beneath furniture. It is not uncommon for homeowners to find large numbers of brown recluse spiders indoors, and most recluse bites that are reported to medical facilities and poison control centers occur on residential properties. Amazingly, a brown recluse spider infestation consisting of more than 2,000 specimens was found within a single-family home back in 2001. Due to their familiarity with manmade structures, massive numbers of brown recluse spiders are able to inhabit homes without drawing attention from residents. These spiders only emerge in open living areas at night to seek out food sources, and they are known for behaving boldly around sleeping humans during this time. For example, doctors recently pulled a brown recluse spider from a woman’s ear. The spider likely crawled into her ear while she was sleeping in her infested home. Brown recluse spiders are not aggressive toward humans and most bites occur when specimens become trapped in clothing or are inadvertently pressed by humans. About 10 percent of all recluse bites result in skin lesions that often develop into necrotic infections that require medical attention.

Have you ever encountered a brown recluse spider indoors?