Awaiting expert review. This page covers safety or regulatory rules that change over time. It is kept out of search results until a qualified reviewer has checked it; the sources below are dated so you can verify each point.
Quick answer
A black widow spider is a shy cobweb spider in the genus Latrodectus whose adult female is shiny black with a red hourglass mark under her round abdomen, and whose venom acts on the nerves.
Bites are rare even where the spiders are common, and nearly all serious ones come from adult females. They hide in dry, cluttered spots around the outside of homes.
Quick facts
The key facts about Black Widow Spider, with sources:
- Genus
- Latrodectus, family Theridiidae (cobweb spiders) 1
- Adult female size
- About 1/2 inch (13 mm) body length, western black widow 1
- Males
- Much smaller than females (one-third the size per USU; one-half to two-thirds the length per UC IPM), tan with white stripes 24
- Eggs
- About 300 per sac; one female can make more than 10 sacs 1
- U.S. range
- Throughout North America, most common in the South and West 3
- Bite frequency
- Quite rare, even where the spiders are very common 1
Key takeaways
- Only the adult female has the classic glossy black body and red hourglass; young spiders and males look striped and tan.
- Black widows live mostly outdoors around homes, in woodpiles, garages, meter boxes and under outdoor furniture.
- The bite may feel like a pinprick, but muscle cramps, sweating and stomach pain can follow within an hour.
- Anyone bitten should get medical care right away; an antivenom exists.
- Cutting clutter, sealing gaps and vacuuming webs does more than spraying.
How to recognize a black widow
A black widow is a spider that builds messy, tangled webs close to the ground and hangs upside down in them at night.
The adult female is the one people picture: jet black, shiny and round, with a red mark on her belly 1.
The CDC lists black widows with brown recluses as the venomous spiders U.S. outdoor workers most need to know 3.
In science terms, widow spiders belong to the genus Latrodectus in the cobweb spider family, Theridiidae. Several black widow species are common in North America, but in the western U.S. the only one is the western black widow, Latrodectus hesperus 1.
The red mark is not always a neat hourglass. UC IPM says it can be a perfect hourglass, two separate triangles, a triangle and a bar, a faint smudge or, rarely, missing 1. A well-fed female can even look plum or brown.
How a black widow hunts and breeds
The black widow’s routine explains where people get bitten.
- Hide by day. She sits in a retreat, such as a gap between bricks, a hole near a pipe or a rodent burrow 1.
- Build at dusk. She repairs her tangled web, which runs from the retreat, and support threads above and below act as trip lines 1.
- Wait upside down. She hangs belly-up in the web, usually within three feet of the ground, catching crawling and flying insects 1.
- Retreat when disturbed. A large shake of the web sends her back into hiding 1. People are most likely to be bitten when they disturb her while cleaning out or picking up stored items 2.
- Lay eggs. A female lays about 300 eggs per sac and can make more than 10 sacs from one mating 1.
- Spread. Tiny spiderlings can “balloon,” floating away on a strand of silk on warm updrafts, a few feet or many miles 1.
- Egg sacYellowish, teardrop shape, tough silk; about 300 eggs
- SpiderlingTan legs, white abdomen with black spots
- ImmatureOlive-gray or tan with white stripes; darkens each molt
- Adult femaleShiny black, red hourglass; about 1/2 inch
- Adult maleStays striped and small; stops eating after maturing
- Back to step 1
Ballooning spiderlings are one reason widows come back to cleared areas. Source: [1] [4]
Widow spiders and close look-alikes
| Spider | Look | Bite risk |
|---|---|---|
| Western black widow (L. hesperus) | Shiny jet black female with red hourglass; about 1/2 inch 1 | The greatest spider venom threat in the western U.S. 1 |
| Brown widow (L. geometricus) | Mottled tan, brown and gray; about 3/8 inch 1 | Much milder bite; tends to drop and play dead 1 |
| False black widow (Steatoda grossa) | Chocolate brown, never red on the belly; about 3/8 inch 1 | Mild; similar to a yellowjacket sting 1 |
| Noble false widow (Steatoda nobilis) | Tan “house with windows” pattern on top; up to 5/8 inch 1 | Not considered medically significant 1 |
The egg sac is often the easiest clue: a brown widow sac has spiky bumps like a big pollen grain, a black widow sac is smooth and teardrop-shaped, and a false widow sac looks like a fluffy cotton ball 1. Our pest identification tool covers other clues.
Example: why one missed female matters
This illustration uses only UC IPM’s published figures. It is not a forecast; most spiderlings die, are eaten or balloon away.
| Step | Published figure | What it means |
|---|---|---|
| Eggs per sac | About 300 1 | One sac can release hundreds of spiderlings |
| Sacs per female | More than 10, from a single mating 1 | One female can produce thousands of eggs |
| Hatch success | No drop in eggs or hatch rate across later sacs 1 | Late sacs are as productive as early ones |
| How close females live | Every few feet, sometimes inches apart, in good habitat 1 | Where you find one, look for more |
Removing egg sacs matters as much as removing spiders, and a vacuum is the simplest tool. UC IPM also notes a 2016 study in which water-based sprays had no significant effect on brown widow eggs inside the sac 1.
Where black widows appear on paperwork
On an inspection report, a technician may note “widow activity” at the garage door, around vents, in meter or irrigation boxes, under decks or in block walls. Good reports also note egg sacs, because they show active breeding.
On a service plan, black widows may be listed as a “venomous spider” add-on or as part of general spider coverage. Check which spiders are covered and whether web removal is included. Our guide to what a pest control contract should say lists the lines to check.
On a product label, spiders must be named as a target pest and the site (indoor, outdoor, crack and crevice) must be allowed. That label is legally binding, as the rules section explains.
In a school or daycare plan, widows are a common reason for routine checks of play equipment and plastic playhouses, which UC IPM names as favored spots 1.
Steps that cut black widow numbers
Extension advice leans on habitat changes. These are the methods with the most support:
- Clearing clutter, woodpiles and heavy ground cover near the house removes the retreats widows need 1.
- Vacuuming webs and spiders works well, because their soft bodies rarely survive it 1.
- Sealing exterior cracks, fitting a tight door sweep and keeping window screens tight keeps spiders out 4.
- Pointing outdoor lights away from doors and windows, or switching bulbs, draws fewer insects and so fewer spiders 14.
- Stacking firewood away from the house and storing garage items in sealed boxes off the floor removes hiding spots 1.
The limits of black widow control
Widows cannot be wiped out around a home. UC IPM says it is not practical to eliminate them, and both widow species re-infest treated areas 1.
Sprays alone fall short, because UC IPM states that insecticides do not give long-term control of widows 1. Many products registered for spiders are water-based, and egg sac silk repels water 1.
New spiders also arrive by air: ballooning spiderlings have been caught 10,000 feet up and 200 miles out to sea 1. A cleared yard can be recolonized from next door.
What shapes the cost of widow control
We do not list prices, because a fair number needs many dated local quotes, but we can name the factors that move a quote.
How much outdoor clutter and structure there is matters most: block walls, decks, sheds and woodpiles all add places to inspect. Whether the plan is one visit or a recurring service matters next, since widows return. Sealing gaps and web sweeping add labor. Schools and rentals may need documented visits, which adds time.
Our recurring plan calculator shows how visit frequency changes the yearly picture, and the cost guide covers how quotes are built.
On guarantees, a plan should say whether call-backs for new webs between visits are free.
How a professional widow service usually works
- Inspect at the right time. Widows come out at dusk, so a technician checks retreats, webs and egg sacs by flashlight or looks for webs near the ground by day 1.
- Remove webs and sacs. Webs, spiders and egg sacs are vacuumed or swept off structures 1.
- Cut habitat. The crew or owner clears debris near the foundation, moves woodpiles and boxes up stored items 1.
- Seal. Cracks, pipe gaps and door edges are closed 4. Our page on caulking to keep pests out covers the materials.
- Treat if needed. A licensed applicator may treat retreats with a product labeled for spiders. UC IPM notes registered options include pyrethrins and pyrethroids 1.
- Follow up. Return visits remove new webs and check favored spots.
If someone is bitten
UC IPM says to seek medical attention at once after a black widow bite; a cold pack can ease pain on the way 1. Children and older adults face more risk 4.
Call 911 for trouble breathing or severe symptoms. Poison Help, 1-800-222-1222, is free and confidential 6. Always wear gloves when clearing woodpiles, boxes or clutter 1.
No permit is needed for a home spider service, but companies and their applicators must be licensed by the state. See how states license pest control work.
A routine that keeps widows down
- Sweep, hose or vacuum webs off the house, garage and fences on a regular schedule 1.
- Check molded plastic toys, playhouses, picnic tables, trash can handles, lawn chairs and pot rims, which have sheltered lips widows like 1.
- Keep gardening gloves and clothes in sealed bags, and shake out boots before wearing them 13.
- Keep the strip next to the foundation clear of leaves, trash and stored materials 1.
- Do not carry plants, firewood or boxes indoors without checking them 1.
Use a flashlight after dark
Widows sit in the middle of their webs at night, belly-up. UC IPM notes a night-time flashlight check is a simple way to find them 1.
Pair this with a broader monitoring habit, and use the seasonal pest calendar to time yard clean-ups.
Black widow bite signs to know
Bites are rare. When they happen, UC IPM and the CDC describe these signs:
- The bite itself may be painless or feel like a pinprick, with two small puncture marks 13.
- A small red mark or red streaks may spread from the bite 1.
- Within about an hour, pain can spread to the chest, belly or whole body 13.
- Rigid stomach muscles, which have been mistaken for appendicitis, plus sweating, sometimes only on the bitten limb 1.
- Less often: numbness, restlessness, fever and patchy weakness 1.
- Unlike recluse bites, black widow bites do not cause much swelling or dying skin 1.
Laws and standards that apply
Federal (EPA, FIFRA). The U.S. EPA registers pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act. Label rules sit in 40 CFR Part 156, and every label says misuse is “a violation of Federal law” 5. A spider product may be used only on the sites and pests its label lists.
Restricted products. UC IPM notes some spider products are sold only to licensed applicators 1. See our guide to safe pesticide use at home.
State. States license pest control businesses and applicators who work for hire. Categories vary by state; check a company with the state license lookup.
Medical care. UC IPM reports that black widow antivenom is made from horse serum, so doctors watch for allergic shock and may choose comfort care instead 1. That is a medical decision, not a pest control one.
Black widow vs brown recluse vs false widow
| Feature | Black widow | Brown recluse | False black widow |
|---|---|---|---|
| Look | Shiny black female, red hourglass 1 | Brown with a dark violin mark, six eyes 3 | Chocolate brown, no red 1 |
| Web | Strong, tangled, near the ground 1 | Thin sheet in a hiding spot | Tangled cobweb |
| Where | Mostly outdoors around homes 1 | Midwestern and southern states 3 | Often indoors on the Pacific Coast 1 |
| Venom acts on | Nerves and muscles 1 | Skin tissue 3 | Mild, local 1 |
| Visible wound | Little swelling, no dying skin 1 | Small blister; sometimes skin damage 3 | Minor swelling 1 |
The full recluse profile is on its own page, listed under related terms.
Black widow myths and facts
- Myth Every black widow has a perfect red hourglass.
- Reality The mark can be split, faint or, rarely, missing, and young widows look tan and striped 1.
- Myth Black widows live inside most homes.
- Reality Black and brown widows are almost never found inside homes, though black widows are common in garages 1.
- Myth A black widow bite leaves a big, rotting wound.
- Reality Black widow bites do not cause notable swelling or dead tissue; the effects are mostly inside the body 1.
- Myth Brown widows are deadlier than black widows.
- Reality Brown widow bites are much milder; they are smaller and likely inject less venom 1.
- Myth One good spray will clear them for good.
- Reality UC IPM says insecticides do not give long-term control and widows re-infest treated areas 1.
How your region changes the species you meet
Which widow you find depends on where you live. The CDC says black widows occur throughout North America but are most common in the southern and western U.S. 3.
In the West, the only black widow is the western black widow, found from British Columbia and Alberta to Mexico and through the Rocky Mountains to the western Great Plains 1.
The brown widow was found only in Florida for decades, then spread through the Gulf Coast states and up the Atlantic coast into South Carolina in the 2000s. By 2016 it was established in Southern California from Santa Barbara to the San Bernardino area 1.
A dark spider with a spiky egg sac on patio furniture in those areas is far more likely a brown widow.
When it matters to you, and the next step
A few webs on a shed or fence call for gloves, a vacuum and a clean-up. Widows near where children play, by doorways or in a garage you use every day call for a full habitat clean-up and sealing. If they keep coming back, or you cannot safely reach the spots, call a licensed company.
When you talk to companies, ask whether they remove webs and egg sacs, what they seal, and how often they return. Our guide to picking a pest control company lists more questions, and the integrated pest management page explains the step-by-step method behind good plans.
Quick decision guide
A web or two in storage: gloves, vacuum and clean up. Widows near play areas or doors: clear habitat and seal. Back every few weeks: a licensed recurring service. Anyone bitten: medical care now.
Questions about Black Widow Spider
How can I tell if a spider is a black widow?
An adult female black widow is shiny jet black with a round abdomen and a red mark, often an hourglass, on her underside.
She is about 1/2 inch long, and the mark varies and can be split or faint.
Young widows and males are tan or gray with white stripes, so look for the tangled, low web and smooth teardrop egg sac too.
Are male black widows dangerous?
Male black widows are not considered a bite risk. UC IPM says almost all medically important bites come from adult females, which are much larger and have stronger biting muscles and more venom.
The UC spider guide adds that male fangs are too small to break human skin. UC sources put males at one-half to two-thirds the female’s length, and Utah State says about one-third her size; either way they are small and look striped.
What happens if a black widow bites you?
A black widow bite often feels like a pinprick at first. Within about an hour, pain may spread, with cramping, rigid stomach muscles and sweating, sometimes only on the bitten limb.
Many cases resemble a bad flu that fades in a few days. Seek medical care right away. An antivenom exists, and severe outcomes are very unlikely with treatment.
Where do black widows hide around a house?
Black widows hide in dry, sheltered, undisturbed spots, usually outside. Common places are woodpiles, block and rock walls, garages near doors and vents, water meter and irrigation boxes, under decks, plastic patio furniture, toys and pot rims.
They tend to build webs within about three feet of the ground. They are almost never found living inside the home itself.
Do black widows live inside houses?
Seldom in living spaces. UC IPM says black and brown widows are almost never found inside homes, because most living spaces do not have enough insects to feed them.
Black widows are common in garages, though, and a spider can be carried in on firewood, plants or boxes. A shiny black spider found indoors on the Pacific Coast is often a false black widow.
What does a black widow egg sac look like?
A black widow egg sac is yellowish and teardrop-shaped, tapered at the top and round at the bottom, with tough, smooth silk. It holds about 300 eggs.
A brown widow sac has spiky bumps like a pollen grain, and a false widow sac looks like fluffy cotton. Vacuum sacs up and seal the bag before throwing it out.
Do pesticides kill black widows?
Products labeled for spiders can kill a widow they contact, but UC IPM says insecticides do not give long-term control, and widows re-infest treated areas.
Water-based sprays also struggle to get through egg sac silk. Removing clutter, sealing gaps and vacuuming webs and sacs work better over time. Any product must be used exactly as its label says.
Is a brown widow as dangerous as a black widow?
The brown widow is less of a threat. UC IPM says the brown widow’s bite is much milder than the black widow’s, mainly because it is smaller and likely injects less venom.
Brown widows also tend to drop from the web and play dead when disturbed. They are common on patio furniture and fences in Florida, the Gulf states and Southern California.
What time of year are black widows most active?
Black widows are active whenever it is warm enough to hunt, coming out at dusk to sit in their webs. Our sources do not give one peak month, and timing varies by region.
Spiderlings disperse by ballooning on warm days with updrafts, which is when new webs may suddenly appear. Regular web sweeping through the warm season keeps numbers down.
Sources
- UC Statewide IPM Program, Pest Notes: Widow Spiders and Their Relatives (Publication 74149), retrieved .
- UC Statewide IPM Program, Pest Notes: Spiders (Publication 7442), retrieved .
- CDC NIOSH, Venomous Spiders, retrieved .
- Utah State University Extension, Black Widow Spider, retrieved .
- U.S. EPA, Introduction to Pesticide Labels, retrieved .
- National Capital Poison Center, About Poison Control (1-800-222-1222), retrieved .
Expert review
Written by the HyrePest Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Identification, egg-sac counts, habitat, range, bite symptoms, antivenom and control limits follow UC IPM Pest Notes 74149 and 7442.
Range and first-aid framing are from CDC NIOSH; male size and IPM steps from Utah State Extension. Label law is from the EPA.
Held (G-REV) until an extension entomologist or medical toxicologist reviews the bite and control content.
Suggest a correction. We fix errors and say what changed.