Black Widow Spiders

There is no metamorphosis here. No larva, no pupa, no caterpillar to moth moment. A spiderling comes out of the sac looking like a small adult in shape if not in color, and it simply molts its way up in size. That matters for a practical reason: there is no vulnerable life stage to time a treatment around, the way there is with an insect. What there is instead is the egg sac, and the sac is the job. Each one can hold 200 to 800 eggs, a single female can produce nine or more of them from one mating, and there is a genuinely obscure finding behind why they survive treatment: egg sac silk repels water, and most registered spider products are water based. In a 2016 study, water based insecticides sprayed onto widow egg sacs had no significant effect on the eggs inside, while petroleum based products penetrated the silk and killed them. That is a single university source relaying a single study, so treat it as a strong lead rather than settled practice, but it explains a lot of failed treatments. On generation counts, no reliable published source states a clean number. What is documented is that a female may produce several sacs across one summer, that adults have been found in Texas buildings in every month of the year, and that colder parts of the range look more like one annual cycle with immatures overwintering.

The hourglass is not always red

The hourglass is not always an hourglass, and it is not always red. UC IPM catalogs five states of the mark on a single species, the western black widow: two perfect triangles joined into a true hourglass; two triangles separated by a gap; a triangle and a small bar; red so minimal it is almost imperceptible; and, on rare occasions, no red at all. By species it gets more specific. The southern black widow normally carries a complete hourglass, often with a single red spot behind the spinnerets. The western black widow's is usually connected, with the front triangle larger and wider than the back one. The northern black widow's hourglass is normally split down the middle, and it usually carries a row of red spots along its back and pale stripes along the sides. Some individuals of both eastern species lack the mark completely. And the brown widow's is orange, not red.

Which widow depends on where you live

Which widow you have depends on where you live, and there are four of them plus an immigrant. The western black widow is the only widow species in the western U.S., running from British Columbia and Alberta to Mexico, throughout the Rockies out to the western Great Plains, and it displaces the southern species in the western half of Texas. The southern black widow covers the Southeast and South Central and reaches as far north as Ohio, Maryland and Pennsylvania. The northern black widow covers the eastern half of the country from southern Canada down to Florida and west to eastern Texas, Oklahoma and Kansas. The red widow is Florida only, which is why a red widow in a Georgia yard is a misidentification. And the introduced brown widow is the one that is moving. It sat in Florida alone for decades, then in the 2000s it spread from Texas across the Gulf Coast and up the Atlantic into South Carolina, and appeared at the same time in huge numbers in Southern California. As of 2016 it was well established from Santa Barbara to San Bernardino and south to Mexico, but not north of the L.A. Basin, not in the Central Valley and not in the deserts. Reports from north of that line were checked and turned out to be immature black widows, false widows or orbweavers.

The one field rule that actually holds

A shiny jet black spider with a round bulbous abdomen, hanging upside down in a tangled web, with any red or orange mark on its belly, is a widow. The absence of a textbook hourglass rules nothing out. Body color is not reliable either: a female with a brownish or plum tinge is usually just a very well fed female whose black abdomen has been stretched until the pigment looks brown.

The male and the juveniles look different

The male and the juveniles look nothing like the female, and neither is a medical concern. This is the fact that most directly reduces a homeowner's fear and almost no consumer page carries it. UC IPM: only the larger immature females and adult females can bite through a person's skin and inject enough venom to cause a painful reaction, and the male has venom but his fangs are too small to break skin. Penn State says the same thing independently: immature and male black widows do not have fangs large enough to pierce human skin, so bites are almost entirely from adult females. The small striped spider in your garage is not the problem. One trap worth pre-empting: the stripe on an immature widow sometimes has a vivid red line inside its white border, and people identify that as an Australian redback. Redbacks do not occur in North America.

Brown widow: the egg sac settles it

Brown widow, and the egg sac settles it in two seconds. A mature female brown widow looks a lot like an immature western black widow, which is the confusion that matters most. Forget the spider and look at the sac. A brown widow's egg sac is covered in silk spikes all over its surface and looks like a very large pollen grain; a black widow's is smooth, tan, teardrop shaped with clean margins. UC IPM says the sac alone is enough to confirm brown widows even when you never see the spider. On the animal itself: the brown widow's hourglass is orange with the bottom half larger and its edges rough, the black spots on its side stripes are large and squarish rather than small and elliptical, and its background is tan rather than olive gray. Dark brown widows are a flat black. Black widows are a shiny black.

False widows are not widows

The false black widow has the same round abdomen, the same cobweb and the same family, but it is chocolate brown and never has any red on the belly. It is slightly smaller at about 3/8 inch, its egg sac looks like a cotton ball with fuzzy edges, and its spiderlings emerge dark like the mother rather than pale. Unlike real widows it genuinely thrives indoors, in washrooms, cupboards and under appliances, which is why it is involved in more bite incidents than black or brown widows. Its venom is mild and produces something like a yellowjacket sting. The noble false widow is bigger, up to 5/8 inch, with a light tan pattern on its back that looks like a house with two windows and a domed roof.

The cellar spider, killed for nothing

The cellar spider is the one people kill by the thousand for nothing. Long thin legs, tiny body, irregular webs in dark places, and it hangs upside down under its web exactly like a widow does. That posture is why it gets mistaken. The tell is the body, not the legs: a widow has a large round bulbous abdomen, and a cellar spider has a small elongate body dwarfed by enormous legs. Cellar spiders are only marginally capable of biting a human because their fangs are too short to pierce skin in most cases, and the University of Kentucky lists them first among common building spiders and calls them harmless. Their only offense is untidy cobwebs. The common house spider is the same story, mottled brown and tan, no shiny black body, no red belly mark, harmless.

Brown recluse, and the eyes settle it

Brown recluse is the other spider people ask about, and the difference is at the eyes. A recluse has six eyes in three pairs arranged in a semicircle; a widow has eight. The recluse carries its violin mark on top of the front body, not underneath. Most usefully: recluse venom causes skin necrosis and widow venom does not. Black widow bites do not cause conspicuous swelling, necrosis or tissue deterioration. If you are looking at a spreading, breaking down skin lesion, you are not looking at the work of a black widow. Brown recluses also do not occur in California.

The web is a tangle, never an orb

You can hear it, too. Irregular, three dimensional, no recognizable pattern, built at night, usually under a foot across and within about three feet of the ground, with vertical trip lines running down to the surface below. There is a retreat hole at one edge, in a brick gap, a pipe penetration or a crevice, and she spends the day in it. The unusual part: widow silk is strong enough that running a finger through a mature web produces an audible ripping sound. No cellar spider or house spider web does that. It is a single source observation, so treat it as a useful field check rather than proof, but it is real enough that the silk was used for gun sight crosshairs in the Second World War.

Sizes, and do not trust a single number

Female body length runs roughly 3/8 to 1/2 inch depending on the species and the population, or about 1.5 to 2 inches with the legs extended. Texas A&M notes outright that sizes vary widely between geographic populations. The male is one half to two thirds her body length, and the male brown widow at 3/16 inch is small enough to be routinely overlooked entirely. The size gap between the sexes is extreme: a female's body can be up to 20 times the male's.

An irregular tangled web near the ground

An irregular, tangled web near ground level, under a foot across, with no orb and no funnel. Look at garage doors, vents, meter boxes, brick veneer, the corners of sheds and crawl spaces, and behind anything stacked and left alone. Widows follow insects, so webs cluster where insects pass.

A retreat hole at one edge of the web

A gap between bricks, a pipe penetration, a rock crevice, an old rodent burrow, with a small silken tent about 1/16 to 5/16 inch across. If you see the web in daylight and not the spider, she is in the hole.

A spider hanging belly-up in the web

A spider hanging upside down in the middle of the web with her belly facing up. That posture is not aggression and it is not unusual. It is the normal resting position, and it is the only reason the hourglass is ever visible.

A tan, teardrop egg sac, guarded

A tan, teardrop or pear shaped egg sac about half an inch across, suspended in the web with a female standing guard nearby. If the sac is bumpy like a large pollen grain, that is a brown widow, not a black widow, and the two are a different conversation.

Webs where people put their hands

Webs on the undersides of things people put their hands on. Picnic tables, lawn chairs, trash can grips, plant pots with curled lips, plastic playhouses and molded toys with spaces facing downward, and the undersides of cheap plastic patio furniture. People find these with a hand rather than an eye, and that is the whole problem. Brown widows also use chain link fences, where black widows generally do not.

Finding several is normal, not an emergency

In habitat that suits them, mature females occur every few feet and sometimes within inches of each other. One spider in a woodpile is background. A dozen webs in a garage you use every day is a management problem.

Nothing to smell

No odor from widow spiders, their webs or their egg sacs is documented. If something smells, it is not this.

A dusty web indoors is an abandoned web

This is a sign by its absence and it is genuinely useful. Occupied webs get maintained, because dust and debris reduce prey capture. A dusty cobweb in a basement corner means the spider has already gone.

Wear gloves

If you do one thing, do that one. Five separate sources say it independently, and it addresses the exact mechanism behind nearly every bite: a hand going somewhere the eyes have not been. Gloves for cleaning out garages and storage areas. Gloves before picking up a piece of firewood, ever. Gloves for basements, attics, garden work, and anything stacked and undisturbed. Add long sleeves, long pants and boots when you are handling piles of stored material.

Look before you reach

Use a flashlight. The recommended way to actually find widows is a night time flashlight search, since they are nocturnal and come out at dusk. Run the beam through cracks, corners, dark undisturbed areas and the undersides of outdoor furniture. Where you can see webs, treat that space as occupied until you have looked properly.

Bag and tape your stored gear

Bag and tape the things you put your hands into. Keep gardening clothes and gloves in bags closed with zipper locks or twist ties, and store outdoor apparel and equipment in tightly closed plastic bags. Store seasonal items, sports gear, camping gear, winter clothes and holiday decorations in boxes taped shut, off the floor and away from walls, with as little empty space between stacked items as you can manage. Almost nobody does this and it costs nothing.

Shake it out

Shoes that have not been worn recently, stored clothing, towels and equipment, before you put them on or pick them up.

Outhouses and outdoor toilets

Check under the seat. This sounds like a joke and it is not. There are many documented bite cases in outhouses, and federal occupational guidance independently lists outdoor toilets with lots of flies as widow habitat. The flies are the reason the spider is there.

Kill the light, cut the food supply

Outdoor lighting pulls in night flying insects, and the insects pull in the widows. Move fixtures off the structure and away from windows and doorways where you can, and switch to yellow or sodium vapor bulbs, which attract far fewer insects. This is upstream of every other control on the list, because the spider is only there for the food.

Clear the foundation line

Keep the strip next to the foundation free of trash, leaf litter, heavy vegetation and stacked materials. Trim shrubs, vines and limbs touching the house. Move firewood away from the building and get it up on a raised structure. Sources that give a distance are not the strongest ones, so take the instruction as away from the house rather than as a specific number of feet.

Seal and screen

Cracks in the foundation, gaps around windows and doors, holes between bricks, and the spaces around pipe penetrations, which are a favorite retreat site. Tight fitting window screens and working door sweeps do double duty, because they also keep out the insects the spiders are hunting.

Vacuum, and destroy the egg sacs

A vacuum or a broom removes spiders, webs and sacs effectively, and widows have soft bodies that usually do not survive the trip through a vacuum. Destroying sacs is the part that matters, since each one can hold hundreds of young. And do not carry them indoors in the first place, on plants, firewood or boxes.

On spraying, the honest version

The university sources are lukewarm and one is blunt. UC IPM says insecticides do not provide long term control against spiders outdoors and should not generally be used, and adds that it is just as easy and much less toxic to crush the spider or vacuum it up. The University of Kentucky is more permissive, naming perimeter barrier sprays applied monthly to bi-monthly in warm months and crack and crevice dusts applied as a barely visible film. It also notes that total release foggers, the bug bombs, are seldom effective. Those two positions have not been reconciled by anybody, and spraying should not be treated as the answer when the strongest source says it is not.

Eradication is not on the table

Nobody can eliminate them, and anyone who tells you otherwise is selling. UC IPM states it plainly: it is not practical to eliminate these spiders completely, and treated areas will be re-infested, because spiderlings balloon in continuously from off your property. What a professional actually delivers is an ongoing management interval and the skill to find and destroy egg sacs in places you cannot reach or see. That is worth paying for. Eradication is not on the table for anyone.

A bite is a medical call

If someone is bitten, that is a medical call and not a pest control call. Stay calm and promptly seek medical advice. Apply a cold pack for the pain. Do not try to draw out or remove venom, and do not try to catch or handle the spider. Poison Control is free, confidential and open 24 hours at 1-800-222-1222. Keep tetanus boosters current, since any bite wound can get infected.

When to Call a Pest Control Professional

Any one of these is enough. You are finding multiple webs with mature females in a space you actually have to use, such as a garage, a crawl space or a meter box. You are finding egg sacs, which means the population is breeding on site rather than passing through. The webs are where children play, under playground equipment or inside molded plastic playhouses. Someone in the household is in the higher risk group, meaning a small child, an older adult, or a person with an existing health problem. Or you are about to disturb a large, long undisturbed store, a woodpile or a shed or a crawl space nobody has entered in years, which is precisely the moment bites happen. The University of Kentucky, a university extension service with nothing to sell, says outright that black widow infestations often require specialized skills and equipment and that it would be prudent to enlist a professional pest control company.