Minnesota is not a region with a high prevalence of medically significant spider species. Most spiders found in the state are harmless to humans, and bites are uncommon. Even when bites occur, the effects are typically minor and localized. Common misconceptions about spider bites frequently lead to misidentification of other insect bites or skin conditions.
Understanding Venomous Spiders
Spiders are often mistakenly referred to as “poisonous,” but the correct term is “venomous.” Poisonous creatures release toxins when ingested or absorbed, whereas venomous animals inject toxins, usually through a bite or sting. Almost all spiders are venomous, using venom to subdue prey, but most spider venom is not potent enough to significantly harm humans. Worldwide, only about 30 spider species are considered medically significant due to their venom’s effects on people.
A spider’s bite typically results in localized reactions, such as mild pain, redness, and swelling at the bite site. Systemic effects are rare and usually associated with bites from a few specific, highly venomous species. Spiders generally bite only when they feel threatened or are accidentally trapped against skin, such as in clothing or bedding. They prefer to avoid human contact and escape rather than bite.
Medically Significant Spiders in Minnesota
In the United States, the black widow and brown recluse spiders are considered the primary medically significant species. While black widow spiders (specifically the Northern black widow, Latrodectus variolus) are indigenous to Minnesota, established populations are not commonly found, and confirmed sightings are rare. These few reported instances often involve spiders transported from other regions. The Northern black widow is characterized by a shiny black body and a red hourglass-shaped marking on its underside. Its venom can cause symptoms like pain, cramping, nausea, and sweating, but fatalities are very uncommon.
Brown recluse spiders (Loxosceles reclusa) are even less likely to be encountered in Minnesota. Their natural range extends only up to Southern Iowa, as they prefer warmer climates. Most alleged brown recluse sightings in Minnesota are misidentifications of other common brown spiders, such as wolf spiders, fishing spiders, or grass spiders. Brown recluse bites, which can cause severe skin damage, are characterized by a pale center that turns dark blue or purple with a red ring, potentially leading to an open sore.
The yellow sac spider (Cheiracanthium mildei) is another spider found throughout Minnesota, including indoors. While venomous, its bite typically causes only mild, localized symptoms like pain, redness, and swelling, similar to a bee sting. The burning sensation usually subsides within hours, and significant tissue damage is not typically associated with their bites. These spiders are active hunters and may bite if trapped against skin, which is why they are sometimes responsible for more human bites than other spiders.
Safety and Prevention
Minimizing encounters with spiders involves several practical steps around the home. Reducing clutter in basements, attics, and garages removes potential hiding spots for spiders. Sealing cracks and crevices in foundations, walls, and around windows and doors can prevent spiders from entering your home. Shaking out clothing, shoes, and towels before use, especially items stored in undisturbed areas, can also help avoid accidental bites.
If a spider bite occurs, cleaning the affected area with soap and water. Applying a cold compress can help reduce pain and swelling. Most spider bites are minor and can be treated at home, with symptoms typically resolving within a few days. However, medical attention should be sought if symptoms worsen, such as spreading redness, increased pain, or if systemic symptoms like fever, chills, or severe cramping develop. Seeking professional medical advice is also advisable if the bite victim is a child, elderly, or has underlying health conditions, or if a black widow or brown recluse bite is suspected.