Widow Spiders (Latrodectus spp) are part of the large Theridiidae family of arachnids, are found worldwide, and are among the most feared.
To date, at least 32 different species of widow spiders have been identified, with at least 5 species found in North America. The two most common North American black widow spiders that have been found to invade home are the Latrodectus Mactans and Latrodectus Various. These cannibalistic, venomous, yet shy spiders, are not common in Canada, preferring warmer temperatures than our Canadian climate. They have made appearances in southern parts of Canadian provinces through mistakenly being transported from the United States to Canada through cargo containing fruits and vegetables.
Like most other spider species, black widows are beneficial to the environment, and help manage and control other pest species like flies, insects, including those harmful to crops (grasshoppers, caterpillars, locusts and beetles). However, it’s bite causes most alarm to humans and can be fatal.
Black widow spiders were named for their nature of killing and devouring their partners post mating. This has only been observed in captivity, and has not been confirmed to happen in the wild. If a female does consume a male, it is done so that the female black widow spider gains nourishment for egg fertilization.
Black widow spiders have shiny jet-black bodies, comb feet and a bright red hourglass shape on the upper side of it’s abdomen. Note that other widow species have red spots or red stripes. Female black widows are almost double the length of males (13mm vs. 6mm).
Black widows are nocturnal, preferring to live in dark or dimly list, undisturbed locations. Common habitats include underneath stones or rocks, in wood piles or freshly lain landscapes, in basements, garages or storage area corners, under furniture, amongst clutter and in areas near and around older, uninhabited buildings. They prefer outdoors, but do end up indoors by accident, most often by being carried in.
Black widows spin webs during daytime, and the female can be observed hanging from the irregular web, clearly displaying her vibrant red hourglass. She does this to warn predators who may try to make her a meal. Black widow spiders are carnivorous and eat flies, mosquitoes, ants, caterpillars, grasshoppers, locusts, caterpillars, millipedes, centipedes, grasshoppers, beetles, woodlice, cockroaches, scorpions and other spiders. They are predatory and use their webs to ensnare their prey. Once captured, they bite their victim to inject their toxic venom, which contains digestive enzymes that liquefies the prey prior to them consuming it.
Black widows only bite when threatened. Their venom is neurotoxic, meaning it directly impacts its victims’ nervous system. Not all bites are fatal if proper medical treatment is given. Aside from pain upon bite, other symptoms experienced by victims of a black widow spider bite include the inability to urinate, rigid abdominal muscles and sweating.
The lifespan of black widow spiders is 1-3 years in the wild, and longer in captivity. Females often live longer than males. Black widow spiders mate from spring into early summer. Amazingly, a female black widow spider can store a male black widow spider’s sperm to produce as many as 10 viable egg sacs, with each containing up to 300 eggs. Egg sacs are paper-like, pear-shaped and 12-15mm in diameter, with white, grey or tan colouring. Black widow spider eggs typically are found under stones, in piles of wood or other natural debris, or in abandoned nests belonging to other animals, like rodents. The female spider protects her eggs until they hatch, which can take up to 30 days.
Post hatching, black widow spiderlings are cannibalistic and will consume one another for nutrients. Spiderlings leave their mother within days of hatching through ballooning. Ballooning is when the spiderlings float away in the air on silk strands to new locations. Once they land, they settle into thier new location by spinning their own webs and capturing food, including other spiders. When the weather cools black widow spiderlings seek protective shelter to overwinter, and emerge in the spring to molt into mature adult spiders.
Black Widow spiders are not common in Canada or Ontario, but there have been rare appearances. Signs that you have a possible infestation include:
Here are tips to prevent a black widow spider infestation:
If you think you have identified a black widow spider infestation, you can attempt to use a vacuum cleaner or broom to collect up the spiders, webs and egg sacs, and immediately dispose in a sealed bag in an outdoor trash can away from your home. This approach is not advised, as it could agitate the spiders and lead to a bite if direct contact is made, as well as miss other spiders that are not visable.
If you have a black widow spider infestation or think you may have one, contact a licensed pest control company to help you safely treat the pest problem.
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