Black Widow Spider

A black widow is a shiny black spider with a round abdomen and a red hourglass mark on its underside; it is one of only two spider groups in the US whose bite is medically significant. It is shy, rarely bites unless pressed against skin, and is easy to control once you know where it lives.

How to identify a black widow spider

The adult female is the one people picture and the one that matters medically:

• Body: glossy, jet-black, with a nearly spherical abdomen. Body length is about 1/2 inch; with legs spread she spans roughly 1.5 inches.
• Hourglass: a red or orange-red hourglass on the belly. In the northern black widow (L. variolus) it is often split into two separate marks, and there may be a row of red spots on the back.
• Legs: long, thin and black, with no bands.
• Behavior: hangs upside down in her web at night, showing the hourglass.

Three species cover most of the country: the southern black widow (Latrodectus mactans) in the Southeast, the northern black widow (L. variolus) in the East and Upper Midwest, and the western black widow (L. hesperus) from Texas to the Pacific and up into western Canada. The brown widow (L. geometricus), a tan relative with an orange hourglass, is now common in Florida, the Gulf Coast and Southern California.

Male black widow

The male black widow spider is a different-looking animal: about half the female's size, slimmer, longer-legged, and usually brown or gray with red and white streaks. Many people never realize they've seen one. Males wander in late summer looking for females and are not considered dangerous.

Baby black widows

Baby black widows hatch pale and turn orange-and-white striped, then brown and black with lighter bands as they grow. A striped juvenile in a cobweb near a woodpile is very often a young widow, even without the solid black color.

Egg sac

The black widow egg sac is round or teardrop-shaped, tan and papery, about the size of a pea or a little larger, and hangs in the web. Each holds a few hundred eggs; hatchlings disperse by ballooning on silk, and most die or are eaten by siblings. If you find sacs, there is an established female nearby.

Black widow web: what to look for

Widows build a cobweb: an irregular three-dimensional tangle with sticky trip lines running down to the ground. The silk is noticeably tough; it "crackles" when you pull through it. Webs sit low, typically within a foot or two of the ground, in protected corners. A classic wheel-shaped orb web in a garden belongs to a harmless orb weaver, not a widow.

Where black widows live

Black widows avoid open living space. Look for them in:

• woodpiles, stacked lumber, stone walls and brush;
• garages, sheds and crawl spaces, especially under shelves and in corners at floor level;
• water-meter boxes, irrigation valve boxes, pool equipment and utility enclosures;
• under patio furniture, grills, outdoor toys and the lips of flower pots;
• inside rarely used gloves, boots and stored boxes.

They are found in every one of the lower 48 states, but they're far more common in the warm South and the West. They're most active from late spring through fall.

How dangerous are black widows?

Black widow venom is a neurotoxin (alpha-latrotoxin). Most bites happen when a spider is accidentally pressed against skin: putting on a glove, reaching under a ledge, rolling over on a stored blanket. The bite may feel like a pinprick. Within an hour, pain can spread from the bite to the abdomen, back or chest, with muscle cramps, sweating, nausea and a rise in blood pressure. This condition is called latrodectism.

Most bites resolve within a few days, and US poison centers have not recorded confirmed deaths in many years. Antivenom exists but is reserved for severe cases. Wash the bite, apply a cold pack, and call Poison Control (1-800-222-1222) or see a doctor if pain spreads or cramps start. See black widow bite symptoms for the full picture.

Black widow look-alikes

Plenty of shiny dark spiders get called widows:

• False widows (Steatoda): similar shape, but brown or purple-brown with no red hourglass.
• Brown widow: tan to brown with an orange hourglass and distinctive spiky egg sacs.
• Redback-like jumping spiders: black and hairy with red on the back, but stocky with big front eyes, and they hop.

More detail with photos is on black widow look-alikes.

Should I kill a black widow spider?

If it lives in a remote corner of the yard you never touch, leave it; it eats pests and won't come to you. If it lives where hands, kids or pets go, remove it:

1. Wear gloves and long sleeves. Use a flashlight in the evening, when the spider sits in the open.
2. Vacuum or crush. A shop vac or a long-handled tool works. Empty the vacuum outdoors into a sealed bag.
3. Destroy egg sacs. Crush or vacuum them; they're tough and sprays often don't penetrate.
4. Spot-spray only if needed. A labeled residual insecticide with an active such as bifenthrin, lambda-cyhalothrin or deltamethrin can be applied to cracks and corners where webs keep appearing. Direct contact sprays kill a spider you can see; residuals work slowly on spiders because they walk on their legs' tips and don't groom much.

Preventing black widows

Prevention is mostly about removing hiding places:

• Stack firewood off the ground and away from the house, and wear gloves when you carry it.
• Clear clutter in garages and sheds; store items in sealed plastic bins rather than cardboard.
• Knock down webs regularly with a broom; widows that keep losing webs tend to move on.
• Seal gaps under garage doors and around pipes; fit door sweeps.
• Shake out gloves, boots and outdoor cushions before use.
• Switch outdoor lights to yellow "bug" bulbs to attract fewer insects, which means less food for spiders.

Sticky traps along garage walls are cheap and show you whether widows are present and where they travel.

When to call a pro

DIY control is enough for a few spiders. Call a licensed pest control company if you keep finding widows indoors, there are many webs in a crawl space you can't easily reach, or you have small children and widows in play areas. Expect roughly $150–$300 for a one-time general pest treatment (approximate; varies by region). A good technician will focus on harborage reduction and crack-and-crevice treatment rather than blanket spraying. See how to get rid of spiders for a full plan.