Black Widow Spider

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  • Colour Of most importance, female black widows are best known for their jet black appearance with red markings on the underbelly
  • Size 6 mm to 13 mm long. The adult female is around 12 to 13mm (not including the legs), and the male is about half that size.
  • Description Black widow spiders are all black to brown in colour and differ slightly in appearance based on gender. The female has a red hourglass-shaped marking on the underside of its globular abdomen, while the male black widows have yellow, red and white bands and spots over their backs, as do both sexes of black widows in their immature stages.
  • Notes Only the adult female black widow is dangerous to humans; males and juveniles are harmless. The female black widow will, on occasion, kill and eat the male after mating.

How to identify Black Widow Spider

Recognizable due to the red hourglass-shaped marking on the underside of the globular abdomen, black widows are jet black in colour. They differ slightly in appearance based on sex, as the underbody of the black widow male features a white marking with red spots. Juveniles appear orange, brown, and white in colour and only achieve the trademark black colouration after multiple molts. Females may grow up to 13 mm long, while males are smaller and measure around 6 mm in length.

Signs of an infestation

The messy, irregular-shaped web of the black widow may be the first sign of an infestation. Typically found under furniture or in the corners of basements and storage areas, webs denote spider activity, whether current or past. In the warmer months during mating season, being bitten by a black widow or encountering large populations of hatching spiderlings generally signals an infestation problem. Seeing adult spiders near or in their webs is the best way to confirm the presence of black widows.

Black Widow Spider Removal

Perhaps the best way to remove black widows from the home is to use a vacuum cleaner. Sweep up the spiders as well as their webs and egg sacs, and promptly dispose of the vacuum bag in an outdoor trash receptacle. If possible, seal the bag in durable plastic. For larger infestations of black widows, call a professional pest control service for effective and appropriate management and control.

How to prevent Black Widow Spider from invading

Reduce clutter in basements and garages by storing items off the floor and away from the wall. Piles of lumber, firewood, stones, or other debris should be moved as far from the home or structure as possible, and stored off the ground. Cut away heavy vegetation and keep tall grasses mowed and trimmed. Repair any holes in brick and exterior stucco. Seal all cracks in the foundation. Use weather stripping around doors and windows. Place screens over vents and other access points. Change outdoor lights to yellow bulbs that deter insects.

Habitat, Diet, and Life Cycle


Black widows prefer to live in dark, undisturbed locations, such as underneath rocks or in wood piles near and around old buildings. They prefer warmer temperatures over colder climates and, as a result, are typically found in the southern portions of the Canadian provinces, in areas near the United States border. Additionally, black widows are known colonizers of freshly disturbed landscapes, such as new-home construction sites. The pests sometimes establish residency indoors, particularly in basements, storage areas, under furniture, or amongst clutter.


Carnivorous and predatory, black widows ensnare their prey in their webs, bite them to inject venom, and then retreat inside the web to finish the meal. The entire digestion process takes place externally, as the spider uses digestive enzymes in its venom to liquefy the prey before it is consumed. Typical prey species include wood lice, millipedes, centipedes, and other arachnids. Black widow males do not feed during mating season and instead focus solely on reproduction.

Life Cycle

Females lay up to 300 eggs in a single, silk-covered egg sac. Uniquely, a female black widow can store the sperm of her male partner to produce up to 10 viable egg sacs, with no diminishment to the number or health of the offspring. The mother spider protects the egg sac from predators and other spiders for up to 30 days until the eggs hatch. Spiderlings stay near the mother for a short period of time before dispersing by way of ballooning, wherein the young use strands of silk to float away. Adult males generally only live long enough to reproduce, while females have been known to live as long as three years in the wild.

Commonly Asked Questions

How worried should I be about black widow spiders?

Black widow spiders are not aggressive to humans, and only bite when threatened, but their venom is a neurotoxin. This affects the nervous system, causing symptoms, such as, abdominal and chest pain, difficulty breathing, nausea, chills, swelling, sweating, weakness and fever. If bitten by a black widow spider, you should seek immediate medical attention.

The female black widow lays approximately 300 eggs. The eggs incubate for some 20 days in a small, round papery sac, that is attached to the mother’s web. After hatching, the baby spiders stay in the cocoon fro up to one month.

Due to the risk of painful bites and the spiders’ potential for rapid reproduction, it is imperative you take action as soon as you suspect an infestation. Only a professional pest control service will be able to stop a black widow spider infestation in their tracks.

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