A spider with a red belly is most likely one of three species: a black widow, a redback spider, or a red-backed jumping spider. The first two are medically significant and worth identifying correctly. The third is harmless. Telling them apart comes down to the shape, size, and exact location of the red marking.
Black Widow: Red Hourglass Underneath
The black widow is the most common red-bellied spider people encounter in North America. Females are shiny black with a red or orange hourglass-shaped marking on the underside of a round abdomen. Their body is about half an inch long, with a total leg span around 1.5 inches. You typically have to see the spider from below, or flip it over, to spot the hourglass. Males are smaller, less distinctive, and rarely noticed.
Young black widows look nothing like adults. Immature females are tan and white with black spots and a striped pattern on the abdomen. As they molt and mature, they gradually darken, losing those lighter markings until the body turns solid, glossy black. Sometimes a fading red or orange stripe is visible on the top of the abdomen during this transition, which can make juveniles harder to identify.
In the western United States, the species present is the western black widow. Its range stretches from British Columbia and Alberta down through Mexico and across the Rocky Mountains to the western Great Plains. They thrive in dry conditions, from California deserts to mountain elevations above 5,000 feet, and they are common in populated areas. Other black widow species cover the southern and eastern United States.
Redback Spider: Red Stripe on Top
If you’re in Australia, the spider you’re looking at is more likely the redback spider, a close relative of the black widow. Female redbacks are black (occasionally brownish) with a prominent orange-to-red stripe running lengthwise along the top of the abdomen. They also have an hourglass-shaped red or orange spot on the underside, similar to a black widow. Juveniles carry additional white markings. Males are light brown with faint white markings and a pale hourglass below.
The key visual difference: a redback’s most visible red marking sits on top of the abdomen like a racing stripe, while a black widow’s hourglass is hidden underneath. Redback spiders are not found in North America, so geography is the simplest way to narrow down which species you’re dealing with.
Brown Widow: Orange Hourglass, Lighter Body
The brown widow is closely related to the black widow but lighter in color, ranging from tan to dark brown or even grayish black. It has an hourglass marking on the underside of the abdomen, but the hourglass is vivid orange or yellow-orange rather than red. The abdomen also lacks the deep, reflective shine of a black widow’s. Brown widows are slightly smaller than black widows and are increasingly common in the southern United States, particularly in urban areas. Their venom is less dangerous than a black widow’s, though bites still cause pain.
Red-Backed Jumping Spider: Bright Red, Compact Body
Not every red-bellied spider is dangerous. The red-backed jumping spider is about a centimeter long with a bright red or orange abdomen on top and a black body and legs. Females have an additional black stripe running down the center of the red abdomen. Both sexes have striking iridescent teal-colored fangs, though you’d need to look closely to notice.
These spiders are found from the Great Plains west to the Pacific coast, from southern Canada into northern Mexico. They prefer relatively dry habitats like coastal dunes and oak woodlands. They’re active hunters rather than web builders, so you’ll often see them jumping on walls or fences in daylight. Their bite is not medically significant.
How to Tell Them Apart
- Shiny black body, red hourglass on the underside: Black widow. Found throughout North America.
- Black body, red stripe on top of the abdomen, hourglass underneath: Redback spider. Found in Australia.
- Tan to brown body, orange hourglass underneath: Brown widow. Increasingly common in the southern U.S.
- Small, compact, bright red abdomen on top, jumps rather than builds webs: Red-backed jumping spider. Harmless.
Size matters for identification. Widow spiders (black, brown, and redback) have round, bulbous abdomens and build messy, tangled webs in sheltered spots like garages, woodpiles, and outdoor furniture. Jumping spiders are noticeably smaller with a compact, almost square body shape and move in short, jerky hops.
What a Widow Spider Bite Feels Like
A black widow or redback bite typically starts as a sharp, immediate sting. Within an hour, the pain can become persistent and feel disproportionately intense compared to the small puncture wound. Local sweating and redness around the bite are common early signs.
Bites are graded by severity. A mild bite causes pain only at the site. A moderate bite brings cramping pain in the large muscles of the torso, along with sweating near the bite. Severe cases, called latrodectism, involve intense muscle cramping across the abdomen, shoulders, chest, and back. Sweating spreads beyond the bite area, and symptoms like headache, nausea, vomiting, and elevated blood pressure can develop. The abdominal pain from severe bites can be intense enough to mimic a surgical emergency.
Most symptoms resolve within one to three days, but lingering muscle spasms, tingling, agitation, and weakness can persist for weeks or even months in serious cases. Deaths are extremely rare with modern medical care, but the experience of a severe bite is painful enough to warrant prompt treatment. If you suspect a widow spider bite, getting medical attention quickly gives you the best chance of managing symptoms before they escalate.
Where Red-Bellied Spiders Hide
Widow spiders favor dark, undisturbed, sheltered spaces. Outdoors, that means woodpiles, rock walls, meter boxes, the undersides of patio furniture, and garden sheds. Indoors, they gravitate toward garages, crawl spaces, closets, and cluttered storage areas. Their webs are irregular and tangled rather than the neat orb-shaped webs you might picture.
You’re most likely to encounter them when reaching into spaces you can’t see into. Wearing gloves while gardening, moving firewood, or cleaning out a garage reduces your risk. Shaking out shoes, gloves, or clothing that has been sitting in a garage or shed is a simple habit that prevents most accidental bites. Reducing clutter in and around your home removes the sheltered spots these spiders prefer.