Missouri is home to two medically significant venomous spiders: the brown recluse and the black widow. These are the only spiders in the state whose bites pose a real health risk to humans. The brown recluse is by far the more commonly encountered of the two, especially in homes, while black widows tend to stay outdoors in sheltered spots. Most other spiders you’ll find around your house or yard are harmless, even if they look intimidating.
Brown Recluse: Missouri’s Most Common Concern
The brown recluse thrives across Missouri and is well adapted to living indoors alongside people. It favors undisturbed spaces: closets, attics, basements, storage boxes, and the gaps behind furniture. Outside, you’ll find them under rocks, logs, and debris piles. They’re not aggressive and typically only bite when accidentally pressed against skin, like when you put on a shoe or shirt they’ve crawled into.
A brown recluse is small. Its body measures about three-eighths of an inch long and never exceeds half an inch, roughly the size of a small fingernail. The legs add to its overall span, but this is not a large spider. Its color ranges from tan to dark brown, and the legs are uniformly light with no stripes or bands. The body is covered in fine hairs rather than spines.
Two features help you confirm an identification. First, look for the dark brown violin-shaped marking on the front section of the body, with the “neck” of the violin pointing toward the back. Second, and more reliable, is the eye arrangement. Most spiders have eight eyes. Brown recluses have six, arranged in three distinct pairs: one pair in front and one pair on each side. You’ll need a magnifying glass to see this clearly, but it’s the single most definitive feature.
What a Brown Recluse Bite Looks Like
Most brown recluse bites are initially painless. You might not even notice the bite at first, though some people feel a mild burning sensation. Within hours, a red bump or plaque develops, often with a pale center that can blister. In the majority of cases, this heals on its own without serious complications.
Skin necrosis, the tissue death that gives brown recluse bites their fearsome reputation, occurs in only 10 to 20 percent of cases. When it does happen, the bite area darkens over several days as the tissue breaks down. A dry, dark scab called an eschar forms and eventually opens into an ulcer. Healing from a necrotic bite can take weeks to months. The venom contains enzymes that break down cell membranes and surrounding tissue, which is why some bites create these slow-healing wounds.
Systemic reactions are rarer but more serious. Over several days, some people develop nausea, vomiting, fever, and general malaise. In severe cases, the venom can trigger destruction of red blood cells, kidney problems, or widespread clotting issues. Bites on the head or neck can cause significant swelling.
Black Widows in Missouri
The southern black widow is the species found in Missouri. Females are the ones to watch for. They’re jet black and shiny, measuring 8 to 13 millimeters in body length (roughly the size of a large pea), with a total leg span of about 25 to 35 millimeters. The classic red or orange hourglass marking sits on the underside of the round abdomen. Some females also have up to four red dots on top of the abdomen, though many don’t. Males are much smaller, only 4 to 6 millimeters, with white markings and red spots on their underside. Males are not considered dangerous.
Black widows prefer outdoor locations with cover: woodpiles, rock walls, sheds, garages, meter boxes, and the undersides of outdoor furniture. They build messy, irregular webs close to the ground. Like brown recluses, they’re not aggressive. Bites usually happen when someone reaches into a spot where a widow has set up her web.
What a Black Widow Bite Feels Like
A black widow bite is a very different experience from a brown recluse bite. The venom contains a toxin that specifically targets the mammalian nervous system, triggering a massive release of chemical signals at nerve endings. The result is intense, spreading muscle pain and cramping that can start within minutes and radiate outward from the bite site. Pain in the abdomen, back, and chest is common. Some people describe it as feeling like severe muscle spasms.
Symptoms can be incapacitating and may persist for days. Sweating, nausea, elevated blood pressure, and difficulty breathing can accompany the pain. Unlike brown recluse bites, black widow bites rarely cause tissue damage at the bite site itself. The danger is systemic: it’s the pain and cardiovascular stress that make these bites a medical emergency, particularly for young children, elderly adults, or people with heart conditions. For severe cases, an antivenom exists and is given intravenously.
Spiders Commonly Mistaken for Dangerous Ones
The vast majority of spiders you’ll encounter in Missouri are harmless, and several get regularly confused with the two dangerous species. Common house spiders have a rounded body shape similar to a black widow’s, but they’re grey with white marbling and banded legs, making them easy to distinguish from the solid black widow once you look closely.
Wolf spiders are large, brown, and hairy, which leads many people to mistake them for brown recluses. But wolf spiders are significantly bigger, have visible stripes or patterns on their legs, and have eight eyes instead of six. They’re also active hunters that run across floors rather than hiding in dark corners. Cellar spiders (the gangly, long-legged spiders common in basements), crab spiders, and yellow garden spiders are other frequent Missouri residents that pose no medical risk.
A good rule of thumb: if the spider is large and conspicuous, it’s almost certainly not a brown recluse. Brown recluses are small, plain, and reclusive by nature. They avoid open spaces.
What to Do if You’re Bitten
If you suspect a bite from either species, clean the wound with mild soap and water. Apply a cool compress for about 15 minutes each hour to reduce pain and swelling. A clean cloth dampened with cold water or wrapped around ice works well. Keep the bite area elevated if possible, and take an over-the-counter pain reliever. Applying antibiotic ointment a few times daily helps prevent secondary infection. If the area is itchy, an antihistamine can help.
The critical thing is to watch the bite closely over the following days. Brown recluse bites that are going to become necrotic typically show clear signs of worsening: increasing redness, a darkening center, or the formation of a blister or open wound. Any of those changes warrant medical attention. For black widow bites, the severe pain and muscle cramping usually make the decision obvious. If you experience spreading pain, difficulty breathing, or systemic symptoms like nausea and fever after any spider bite, seek medical care promptly.
Reducing Your Risk at Home
Because brown recluses are so common indoors in Missouri, practical prevention matters more than identification after the fact. Shake out shoes, gloves, and clothing that have been sitting undisturbed, especially in closets, garages, or basements. Wear gloves when moving boxes, firewood, or items in storage. Reduce clutter in storage areas since brown recluses love cardboard boxes and undisturbed piles. Sticky traps placed along walls and in closets are an effective, low-effort way to monitor and reduce indoor spider populations.
For black widows, be cautious when reaching into dark outdoor spaces: woodpiles, rock crevices, utility boxes, and the undersides of patio furniture. A quick visual check before sticking your hand somewhere is the simplest protection. Keeping outdoor areas tidy and reducing ground-level debris removes the sheltered spots widows prefer.