What does a female black widow look like

A female black widow spider (Photo from the Wikipedia Commons)

There are two species of black widow spider in Canada: the western black widow found in parts of BC through to Manitoba (mostly restricted to areas close to the southern Canada-U.S. border) and the northern black widow in southern and eastern Ontario. On occasion, black widow spiders occur outside of their ranges by hitching a ride on produce such as grapes.

Generally, only females are cause for concern. Even then the small amount of venom they produce gets quickly diluted by the human body. A black widow bite can, however, cause severe pain at the bite site and lead to painful muscle contractions. Although these bites are generally not life-threatening for healthy adults, medical attention should always be sought following a black widow bite — particularly for children and the elderly.

Now that we've allayed your fears (we hope!), read on and learn more about this amazing arachnid.

It's all in the name

Aside from being a popular comic book character, the black widow spider is notoriously known — and named — for the behaviour of its females. While humans may have little to fear, the same cannot be said for a female black widow's mate. In some cases, females kill and eat their partner after mating.

Sexual cannibalism, as it's called, may serve a greater purpose. Females who eat males have been found to have healthier broods. A male benefits by giving its offspring a better chance of survival. But it may not be all about selfless sacrifice. Recent studies showed that males could sense hungrier females and avoid them. By using scent receptors in their feet, males could tell from a female's web if she was likely to eat him and choose a safe mate.

But with behaviour like that, it shouldn't be much of a surprise that offspring are cannibalistic too, eating each other as they hatch from their eggs.

Hourglass figure

While the common image of the black widow is its all-black body, eight spindly legs and signature red hourglass boldly displayed across its abdomen, that description is strictly for the ladies.

Males are about half the size of a female, and are brown or grey in colour with varied markings, including white stripes and red spots. Juveniles meanwhile develop a mixed colouration of orange, brown and white.

Fact: there are five different species of black widow found across North America.

Where, oh where, can they be?

(Click on the image to enlarge)

Black widows are found in the southernmost regions of at least five provinces in Canada, from BC across to Ontario and across the continental U.S. The largest population in Canada is found in Ontario.

Given its need for a warmer climate, the black widow's distribution is not surprising since Ontario dips farther south than any other Canadian province.

You can rest assured you're unlikely to find them in your home, at least. Black widows prefer dark, sheltered spots close to the ground, such as wood, trash or rock piles, or even underneath a house. Here, they spin funnel-shaped webs to catch their insect prey.

The key to relationships is communication

The webs of black widows aren't just for catching dinner. They also come in handy to communicate with mates. When looking for a partner, male black widows will vibrate the silky ends of a female's web to alert them of the male's presence. Only after a complicated dance by the male, and if a female accepts, will they mate. The female then lays 50 to 100 eggs, wrapped in silk for protection, and 30 days later the spiderlings hatch.

Fact: newly hatched spiderlings are all white.

Just one bite, and its prey melts...literally

The venom of black widow spiders is actually 15 times stronger than that of rattlesnakes. Fortunately for people, black widow spiders bite only when disturbed and often do not inject venom. However, this is still bad news for bugs. Smaller insects that get caught in the spider's web are paralyzed with venom and carried home for dinner. Black widows use an enzyme to help them digest their victims, leaving only empty carcasses.

Sources

Canadian Geographic, Animal Facts: The Black Widow Spider
CTV, Black Widow Spiders in Ontario not cause for alarm
Enchanted Learning, Black Widow Spiders
Mother Nature Network

• 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

Habitat

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.

Diet

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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