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Black widow spider
© istockphoto.com/Mark Kostich

Fast Facts: Black widow spider


Scientific name: Latrodectus mactans
Average weight: 1 g
Average length: 3-4 mm (males), 8-10mm (females)
Average lifespan: 1-2 months (males), up to 3 years (females)

Did you know?


The black widow spider’s venom is 15 times more poisonous than that of a rattlesnake! But, the amount of venom a spider injects with one bite is usually not fatal for humans.

Physiology


Black widow spiders are also known as “comb-footed” or “tangle-web” spiders. Both names are appropriate for the fingernail-sized black widow, which builds irregular, funnel-shaped tangle webs and traps prey using its combed hind pair of limbs.

Juvenile spiders are orange, brown and white and acquire their signature charcoal color as they age and molt. Adult females have a red hourglass mark on their abdomen and one or two red spots over the spinnerets and along the middle of the back. Males are usually about half the body size of the females, but have longer legs. Their joints are orange-brown in the center and black on the ends and they usually have four pairs of red and white stripes on the sides of their abdomen.


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Habitats/Behaviours


click for larger image
Black widow spiders are found in the warm, dry parts of the world and prefer to spin their webs in dark, sheltered spots close to the ground. The web itself is an amazing structure, serving as a home for the spider, a defense against predators, an effective trap for prey and a means of communication between males and females.

Both predators and prey get entangled in the snare. When this happens, the spider wraps more silk around the unlucky victim and paralyzes it with venom. The spider then drags the bundle back to its home to enjoy its feast. Digestion actually takes place outside of the body: the spider pours digestive enzymes on its prey to break it down before consuming it.

During mating season, the male no longer feeds and expends most of its energy finding a mate. When he does find a female, the male vibrates the threads of her web to make sure that she is a female of the same species and to alert her of his presence.

A female lays 50-100 eggs onto a small web and covers them with silk for protection. The female then guards the egg sac for about 30 days until the spiderlings hatch.

Range


The black widow spider is found in warmer regions of the world, up to southern Ontario. It inhabits various habitats, including temperate forests, temperate grasslands, tropical rainforests, chaparrals and deserts.

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