In the southern United States, a quiet yet widespread invasion is underway. Once confined to the humid subtropical climate of the Florida peninsula, the brown widow (Latrodectus geometricus) has now established a permanent foothold as far west as California and north as South Carolina, and it has even been recorded in southern Canada. Though its bite is less lethal than that of some of its relatives, the brown widow remains a serious hazard that deserves attention.
All widow spiders are dangerous because of their venom, a neurotoxin called latrotoxin. The most common symptom of a brown widow bite is a burning pain at the site, but patients often report additional discomfort in nearby lymph nodes, leg weakness, or abdominal muscle pain. The reason a brown widow bite is typically less severe than those of other widow species is that it delivers a smaller dose of venom. Nonetheless, the brown widow may be the most venomous spider in North America. A 1989 article in the South African Journal of Science compared the toxicity of several Latrodectus species and found that the brown widow’s venom was three to five times more lethal than that of North American widow spiders, yet it delivered significantly less venom per bite.
First described in Colombia in the 1840s, the brown widow is believed to have been introduced to the New World from Africa. The first recorded observation in the United States occurred in Florida in the 1930s, where the species remained for roughly six decades. In the 1990s, brown widows began appearing in warm coastal states across the country, and over the past decade they have been spotted in Oregon and Pennsylvania (though not in Alaska). Globally, they are present on every continent except Europe and Antarctica.
As an invasive species, the brown widow excels at displacing native spider populations. A 2008 study of its spread in southern California documented the brown widow’s ability to outcompete local western black widows. Similar findings were reported in Hawaii and the Caribbean, where brown widows have displaced native black widow species.
These spiders thrive on human-made structures, making them peridomestic. They are often found on cars and RVs—a convenient vector that facilitates their continued expansion.
Brett_hondow/Getty Images
Prevention is the most effective strategy for managing brown widows. Remove any food sources that might attract them: a single egg sac can contain 50 to 250 spiderlings. A 2026 study in the Journal of Arachnology found that when food is plentiful, up to 60% of the spiders survive; with limited resources, fewer than 10% do. Keeping your yard clean and your trash bins sealed reduces the available prey.
If you already have an infestation, an oil-based pesticide can be used to sterilize egg sacs before they hatch. For those who prefer to avoid chemical treatments, thorough cleaning—removing clutter both inside and outside—reduces the places where webs can form. Additionally, seal gaps around doors, windows, and foundations to keep spiders from entering.
Brown widows are likely here to stay. Unlike their New Zealand cousins, they are a cosmopolitan species with a broad distribution. In areas where they are established, the best defense for your pets and family is rigorous prevention: keep food out, maintain a tidy environment, and seal entry points.
