Black Widow Spiders

There are several widow spiders in the United States, they are not equally dangerous, and the marking everyone knows about is less dependable than its reputation. This page keeps the species apart, keeps the disagreements visible, and reports the medical material from named sources without grading any of it.

Eight products are named further down, all of them for keeping spiders out of a building or for taking a web down from a distance. Every link is a plain product link and PestPro Index earns nothing if you buy any of them; each card says so immediately above its own link.

Which Widow, and the Hourglass

The hourglass tells three species apart — and three sources say it can be faint or missing

Kansas State University Extension uses the marking as the species character, for the three that live in Kansas: the northern (Latrodectus variolus) has an hourglass that is broken, with a row of red spots down the middle of the top of the abdomen; the southern (L. mactans) has a complete hourglass and one red spot just above and behind the spinnerets; the western (L. hesperus) has a complete hourglass and the rest of the abdomen solid black.

UC IPM, on the western species: “The red hourglass varies in appearance” — it can be two perfect triangles merged, two triangles separated by a space, a triangle and a small bar, minimal or almost imperceptible red coloration, or, in its words, on rare occasions completely absent.

Colorado State, on the same species: the pattern “may appear as two unconnected spots, as a roughly rectangular area, or be so faint as to be barely visible.” It adds that the colour may fade or intensify during the life of any individual.

UF/IFAS compares three species directly: “The Southern black widow has a complete hourglass, while the Western species’ hourglass can vary from two connected triangles to separated triangles to a minimum of barely visible red blotches. The Northern widow typically has the hourglass on their abdomen, but some individuals lack it completely”.

Immatures and males look like something else entirely

UC IPM: “As easy as it is to identify an adult female black widow, the immatures, looking nothing like the mother, can be difficult to recognize.” Spiderlings emerge with tan legs and a mostly white abdomen, and darken through successive molts.

This matters less than it sounds for bites. Penn State: “Immature and male black widows do not possess fangs large enough to pierce human skin, so bites are almost entirely due to adult female spiders, especially females protecting an egg sac.” UC IPM: “Almost all medically important black widow bites are from the adult female, which is much larger than the male.”

One caution comes from a single source and is given as that source’s. Kansas State states that male and immature widows do not produce the same toxic venom as females, but that young spiderlings carry a toxic substance in their bodies that may harm pets or children if swallowed. No other source consulted for this page mentions it.

The lookalike that is not a widow

Colorado State, on Steatoda cobweb spiders: “they lack the orange-red hourglass on the underside of the abdomen, have prominent white markings on the top of the abdomen, and often have a white band around the anterior edge of the abdomen.” UC IPM: the false black widow “is chocolate brown and never has red coloration, although many people frequently mistake it for a black widow.”

Penn State publishes a separate page on it, and two things there are worth having. “False black widows produce symptoms that are similar to but much less severe than those of a true black widow bite.” And Steatoda grossa is reported to prey on other spiders, including true black widows — which is a reason to know which one is in the corner before killing it.

⚠ The folklore in the name: two sources say it is wrong

Penn State states it as fact: “Males are often killed and eaten by the females shortly after mating, thus the origin of the name ‘widow’.”

Colorado State contradicts it: “Although females of many spider species, including widow spiders, occasionally feed on males if the female is hungry, this cannibalistic behavior is not the norm despite the common misconception.” Kansas State agrees with Colorado State: “Although observed, this behavior is uncommon.” It adds that males typically leave quickly after mating and often stay near the web, feeding on prey the female has caught.

Colorado State offers a different origin for the name altogether: that widow spiders are called that because they are shiny black when full grown, and black is a traditional colour of mourning. Two against one, and the disagreement stands rather than being settled.

Where Each Species Is

Every range statement below is scoped to one species. They are not one map.

• Western black widow, per UC IPM: “Its habitat ranges from British Columbia and Alberta to Mexico and throughout the Rocky Mountains to the western portions of the Great Plains.” Outside California it is common in urban Colorado, in central and eastern Washington state and in southern British Columbia.
• Southern black widow, per UF/IFAS: “In the United States, the Southern black widow is found in the southeastern region and has been found as far north as Ohio and as far west as Texas.”
• Pennsylvania, per Penn State: the southern black widow is found there, and “It is probable that the northern black widow, L. variolus , is also present.” The hedge is the source’s and is kept.
• Kansas, per K-State: three species — northern, southern and western.
• California, per UC IPM: two — the western black widow and the brown widow.

The brown widow’s range is a moving story and its dates matter. UC IPM: “In North America, the brown widow was found only in Florida for many decades, where it remains rather common. However, in the first decade of the 21st century, the spider began appearing elsewhere, from Texas throughout the Gulf Coast states and up the Atlantic coast into South Carolina.” UC Riverside dates the western arrival precisely: “In February of 2003, specimens of the non-native brown widow spider, Latrodectus geometricus , were discovered as part of the Los Angeles Spider Survey being conducted by the Los Angeles County Museum of Natural History.” Both statements are about a range that was expanding when they were written. The first-decade phrasing is now more than fifteen years old and this page does not present it as a current front.

What a Bite Does

Everything in this section is reported from a named source. None of it is this site’s assessment and none of it is graded here.

How rare, and how it happens

UC IPM: “Bites from black widow spiders are quite rare, even where these spiders are very common.” Colorado State: “the western widow is not aggressive, and bites are very infrequent even when large numbers of spiders occupy an area”, and “Widow spiders rarely, if ever, bite when not within a web.” Colorado State adds that most bites happen when somebody inadvertently presses down on a spider resting under a rock or under wood in a wood pile.

⚠ What the bite itself feels like: the sources do not agree

UC IPM: “the bite itself is painless or may feel like a little pinprick”. Penn State: “Black widow venom is principally neurotoxic, so at first a bite is almost painless.” Colorado State: “The bite can go unnoticed, although it most often produces an immediate sharp, pin-prick pain.”

Colorado State’s “most often produces an immediate sharp pain” is not UC IPM’s “painless”. Both are published positions from extension services and neither is corrected here.

⚠ Onset and duration: four sources, four timelines

These are four different courses and the outer bounds differ by an order of magnitude — “a few days” against “up to a month”. They are not averaged and not merged into one range. UF/IFAS’s figure is also conditioned on treatment, which the other three are not, so it is not comparable to them even in principle.

What the symptoms are

UC IPM lists rigid stomach muscles “which some medical professionals have misdiagnosed as appendicitis”, sweating that is sometimes confined to the bitten limb, pain that can be local, radiating or regional, urine retention, and less commonly numbness, agitation, fever and patchy paralysis. It then supplies the proportion itself: “Although these are the most severe manifestations of black widow bites, symptoms most often merely resemble those of the flu.”

One negative separates this spider from the other one people fear. UC IPM: “Black widow bites don’t cause conspicuous swelling, necrosis, or deterioration of tissue around the bite.” If a wound is doing that, the widow literature is not where the answer is; our brown recluse page sets out what the sources there say about necrotic wounds and how often they are misattributed.

Colorado State: “Muscle and chest pain or tightness are some of the most common reactions to the widow toxin.” Kansas State states that reactions vary with the age and health of the person bitten and the part of the body bitten, and that the very young and very old are most likely to be severely affected.

⚠ Deaths: four sources, two framings

Penn State, citing the American Association of Poison Control Centers, states that “approximately 2,200 people are bitten in the United States by black widows every year, but no deaths have been recorded due to black widow bites since 1983”. Both halves of that are one sentence in the source and are kept together. UC Riverside, writing about southern California, says in passing that black widow bites do occasionally happen and no one dies.

Kansas State states that “In severe but rare cases, bites result in tremors, convulsions, difficulty breathing, and death due to suffocation.” Utah State lists the outcomes as “pain, nausea, cramping or death (rare)” and states that a bite “can be a serious health risk, especially to children and elderly people”.

Two sources report no deaths in the data they cite; two describe death as a rare possible outcome. Neither pair is used here to cancel the other.

⚠ The brown widow is a separate question with a separate answer

UC IPM: “unlike that of the black widow, the bite of this spider is not much more toxic to humans than that of other common spiders.” UC Riverside: “The brown widow is not a spider of medical concern and is not likely to become one.” Its evidence is a South African series in which, in its words, “Only two symptoms of brown widow envenomation were reported in the majority of bite victims: 1) pain while being bitten and 2) a mark where the bite occurred.”

And the counter-evidence sits in the bibliography of one of those same two sources. UC IPM’s reference list cites a 2008 paper in the Southern Medical Journal reporting a severe reaction from a brown widow envenomation. That paper was not read for this page and nothing is claimed about what it found. Its existence, cited by a source that calls the bite minor, is the honest shape of the evidence and is given as such.

A separate count, from a different source and a single year

UF/IFAS publishes a figure of its own for one year: “In 2010, there were 2,168 self-reported black widow bites reported in the United States, with 892 cases treated in health care facilities”. In that survey there were no deaths.

If You Think You Have Been Bitten

Antivenom: it exists, and the sources describe its use differently

UC IPM: “An antivenom for black widow bites is available that works for all species that have been tested worldwide.” It states that response is fast, and then gives the constraint: “The antivenom is based on horse serum, so physicians need to monitor for anaphylactic shock. American physicians are somewhat reluctant to use antivenom for this reason and might prefer to have the bite victim simply endure the symptoms, which can be similar to those of a bad flu episode and usually dissipate in a few days.”

Penn State: “Latrodectus antivenin is available, but it is generally reserved for extreme cases as there is a risk of anaphylaxis (allergic reaction) to the antivenin.”

UF/IFAS publishes a fuller clinical account of when antivenin is used, how it is produced, which patients it suits and how quickly it is given. That is a clinical decision and it is named here rather than reproduced. This page reports that the antivenom exists, what it is made from, and why the sources describe its use as restricted. It does not say when it should be given, to whom, or how soon.

What else is deliberately not on this page. UF/IFAS also publishes the drugs used in treatment and a review of what did and did not relieve symptoms, and a body of material about bites during pregnancy beyond the single instruction quoted above. All of it is clinician material. It is named as existing and none of it is set out here.

Where They Live, and Taking Webs Down

The sources describe the same habitat. Colorado State: widow spiders “often live in ready-made holes in dark, undisturbed sites” and are most often found in abandoned rodent burrows, loose stone or wood piles, or the corners of rooms, garages and outbuildings. K-State adds electrical and water meter boxes, old cars, unused farm equipment and infrequently used lawn furniture. Utah State lists building foundations, rock piles, wood piles, outbuildings, water meter and irrigation boxes and the area around exterior lighting.

UC IPM on why lighting matters: “Outdoor lighting attracts insects, which in turn attract spiders. If possible, keep lighting fixtures pointed off structures and away from windows and doorways.” Utah State’s version of the same measure is to change exterior lighting to sodium vapor bulbs.

Physical removal is what the sources put first. Colorado State describes searching for them and destroying them by crushing or vacuuming the web and the spider, using protective methods, and elsewhere ranks physical search and removal ahead of the other treatments it discusses. That ranking is a paraphrase: the publication states it with a superlative this site does not print, and the instruction rather than the wording is what is carried here. UC IPM: “Vacuuming spiders can be an effective control technique because their soft bodies usually don’t survive this process.”

Kansas State names the tool: “If black widows are found, carefully remove and destroy spiders, webbing, and all egg sacs. This can be done with a broom or other long-handled device, or a vacuum cleaner.”

Colorado State adds an egg-sac method that costs nothing: crushing them, or freezing them — it says to leave them in the freezer for several weeks.

And the honest ceiling, from UC IPM: “However, it is not practical to eliminate these spiders completely. Both widow species will continue to re-infest treated areas.” The reason is ballooning: spiderlings climb up, release a filament of silk and are carried off on updrafts, so “Because spiderlings will be dropping down on your property continually, eliminating them will be a task that needs to be done repeatedly throughout the year.” Kansas State puts the same limit differently: “It is difficult to locate and destroy all spiders without thoroughly cleaning the area.”

Worth noticing: not one source consulted for this page routes this job to a professional. That is a real difference from what the same kind of sources say about the brown recluse, where two of them do. The widow sources describe a job a householder does — bounded by permanence, not by competence.

Handling Stored Things and Woodpiles

UC IPM attaches gloves to two specific moments: “When cleaning up clutter in garages and other storage areas, be sure to wear gloves to avoid accidental bites.” and “Stack woodpiles away from your house, and never pick up pieces of wood unless you are wearing gloves.”

Two sources specify what kind. Kansas State: “Wear leather gloves, boots, socks, long-sleeved shirts, and long pants made of thick material when working in areas known to be infested with black widow spiders or where contact is likely.” Colorado State asks for “heavy, leather gloves”, and separately that “It is also a good idea to wear gloves and a long-sleeved shirt when working in spider infested areas.” UF/IFAS asks more loosely for gardening gloves.

What to keep things in

UC IPM: “In the garage, keep items such as gardening clothes and gloves in bags closed with zipper-locks or twist ties. Store seasonal items such as sports gear, camping gear, winter clothes or holiday decorations in boxes that can be taped shut and placed off the floor away from walls in order to exclude spiders.”

It also names the places people forget: “Other areas to check carefully include children’s toys or playhouses made of molded plastic that have open spaces facing downward where spiders can crawl in.” and picnic tables, trash can grips, lawn chairs and plant pots with curled lips.

Keeping Them Out

Kansas State: where possible, seal cracks around doors and windows and repair holes in screens, to prevent spiders from entering structures. It also notes that the undisturbed places widows like are good habitat for brown recluse spiders too, so the same clearing out reduces both.

Utah State’s IPM list gives the same measures as separate lines: minimise nesting habitat, seal exterior cracks and crevices to reduce hiding places, reduce clutter indoors and outdoors, “Install tight-fitting door sweeps.”, install tight-fitting screens in windows, and reduce the other insects that serve as food.

UC IPM describes the same job at the garage: “block off house access to spiders by sealing cracks around doors and access holes for electrical conduits or plumbing”, and adds keeping areas near building foundations free of trash, leaf litter and accumulated materials.

Insecticides, and Why Nothing Is Named Here

The sources take four positions on whether insecticides do anything useful against widow spiders.

• UC IPM: “Insecticides do not provide long-term control.” and “Typically, control of spiders using pesticides is difficult.”
• Colorado State: “Insecticides can be useful for adult spider control but are not particularly effective against egg sacs.” It names four pyrethroids sold for general spider control around a home — bifenthrin, cyfluthrin, permethrin and tetramethrin — with some residual effectiveness of several weeks, particularly if not exposed to light and moisture. Of a perimeter treatment it says: “However, the benefit from such treatment will be short-lived.”
• Kansas State: spot treatment of the areas widows inhabit can be used, but general crack-and-crevice applications are unlikely to work because the pesticide does not come into contact with the spiders. That sentence is a paraphrase — the published text is broken across a line in the source PDF and this page does not quote across such a break.
• Utah State lists no insecticide at all among its recommendations.

UC IPM publishes one finding specific enough to shop against, and it is about egg sacs rather than spiders: “In a 2016 study, water-based insecticides sprayed on brown widow egg sacs provided no significant effect on the egg contents. However, when petroleum-based products were used, the pesticide was readily carried past the silk outer layer and killed the egg sac contents.”

One class the sources reject outright. Colorado State: “A large number of controls are sometimes promoted for control of spiders, including widows. These include various chemical repellents (e.g., mock orange, garlic) or ultrasonic frequencies – neither of which spiders perceive or respond to.” Nothing of that kind is named here either.

And one finding about how insecticides act indirectly, from Kansas State: spiders that ate insecticide-killed prey did not die from that secondary exposure, but insecticide use reduced or eliminated the arthropod prey, which limits what the population has to live on over time.

Questions

Sources

1. UC Statewide IPM Program (R. S. Vetter). Widow Spiders and Their Relatives — the source of the western black widow range, the hourglass variability, the medical aspects and antivenom account, the brown widow comparison, the ballooning limit, the 2016 egg-sac formulation study and most of the habitat guidance. Accessed 26 August 2026. https://ipm.ucanr.edu/home-and-landscape/widow-spiders-and-their-relatives/
2. Penn State Extension (Steve Jacobs). Southern Black Widow Spider — the source of the five-species United States list, the symptom timings, the antivenin position and the Poison Control Centers figure. Updated 8 September 2025; accessed 26 August 2026. https://extension.psu.edu/southern-black-widow-spider
3. Colorado State University Extension. Western Widow Spider — the source of the Steatoda comparison, the symptom duration, the cannibalism correction, the physical-removal position and the repellent and ultrasonic finding. Accessed 26 August 2026. https://extension.colostate.edu/resource/western-widow-spider/
4. University of Florida IFAS Extension. Southern Black Widow, Latrodectus mactans (EENY-560/IN1000) — the source of the southern species range, the 2010 Poison Control figures, the recovery timings and the pregnancy instruction. Accessed 26 August 2026. https://edis.ifas.ufl.edu/publication/in1000
5. Kansas State University Agricultural Experiment Station and Cooperative Extension Service (R. Jeff Whitworth and Holly Schwarting). Structural Pests: Black Widow Spiders (MF3346) — the source of the three-species hourglass table, the first-aid list, the leather glove and long-handled removal instructions and the crack-and-crevice finding. March 2017; accessed 26 August 2026. https://bookstore.ksre.ksu.edu/pubs/MF3346.pdf
6. University of California, Riverside, Department of Entomology (Rick Vetter). The Brown Widow in Southern California — the source of the 2003 Los Angeles discovery and of the position that the brown widow is not a spider of medical concern. Undated in page; describes a February 2003 discovery; accessed 26 August 2026. https://spiders.ucr.edu/brown-widow-spiders
7. Utah State University Extension. Black Widow Spider (Urban Pest Guide) — the source of the door sweep, window screen and exterior lighting items, and of the outcomes list for a bite. Accessed 26 August 2026. https://extension.usu.edu/pests/ipm/notes_nuisance/black-widow.php
8. Penn State Extension (Steve Jacobs). False Black Widow Spider — the source of the Steatoda grossa description and of the statement that its bite symptoms are much less severe. Updated 8 September 2025; accessed 26 August 2026. https://extension.psu.edu/false-black-widow-spider
9. University of Kentucky (Lee Townsend and Ken Yeargan). Common Spiders Found Around Homes and Buildings (ENTFACT-622) — cited only for its statement that few spider species have venom of consequence to people. Accessed 26 August 2026. https://entomology.ca.uky.edu/files/ef622.pdf