Western Black Widow Spider Fact File
Western black widow spiders exhibit sexual dimorphism between the males and females.
The female is most recognizable by hrt large black body which is shiny and has a reddish hourglass shape on the underside of the very round abdomen.
Males are typically around half the size of the females though their legs tend to be longer. Their body is covered with yellow and red bands that is patterned with spots.
Western black widow spiders are part of the comb-footed spider group and have stiff, jagged hairs on the back of their legs which are used to wrap their prey in silk.
As a spider they have four pairs of legs which each end with a claw.
Females reach a length up to 3.8cm (1.5in) long while males measure up to 1.25cm (0.5in) long. An average weight for this species is 25g (0.88oz).
Western black widow spiders are carnivores. They feed on small insects such as flies, mosquitos, grasshoppers, beetles and caterpillars.
These insects are caught in the web which is formed from silk. They will then wrap their prey in silk and carry it to a rest site where it is eaten.
They have the ability to go for months at a time without eating.
Male 4 months
Female 1.5 years
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North America is the native home of the western black widow spider. Here they can be found in the west of the United States and in Canada.
They make their home in desert areas. Most often they are seen under ledges, rocks and plants. During cold weather they will often enter homes.
The name of the western black widow spider comes from their mating habits. Females often eat their partner at the end of mating.
Breeding takes place in late spring. Males will form a small sperm web where they can deposit the semen. From this they cover the pedipalps in sperm and travel to find the female.
Their courtship sees the male vibrate the threads of silk making up a female’s web to make her aware of his presence. A receptive female will allow him to insert his papal organ and then begin to release her eggs. These are laid on the small web and covered with silk. More silk will be added until the eggs are fully enclosed in a cocoon of silk.
Once the mating is complete the female may eat her mate but this does not always occur. Males make an effort to determine if the female has recently eaten which will reduce his chance of being eaten.
A female guards her egg sac which may include anywhere between 20 and 900 eggs. The egg sac is white or tan in color. Once the eggs hatch they receive no further care from the parents. The eggs incubate for 14 days before hatching.
She may store sperm and use it to produce eggs for the rest of her life.
Males mature after 70 days old while the females take 90 days to mature.
Few of the hatchlings will survive to adulthood and they are cannibalistic eating their own siblings.
Outside of the breeding season western black widow spiders are solitary, living on their own nest. They are primarily active by night.
Western black widow spiders have a venom which is 15 times more potent than that of rattlesnakes. Despite this the small amount injected means deaths are rare. That being said if bitten by a spider one should always seek medical care.
Predators and Threats
Only one predator has been recorded for the black widow spider, the mud-dauber wasp.
If disturbed by a predator the black widow spider will fall out of its web and play dead.
Females will display their red hourglass marking while sitting on her web which acts as a warning to predators that she has a potent venom to use in her defense.
Western black widow spiders are one of the five widow spider species.
The western black widow spider creates silk which is being studied by scientists to see if they can create a similar substance to create thread and rope from which would be incredibly strong. Their silk is tougher than kevlar, the substance used in bulletproof vests.
By Steve Ryan – https://www.flickr.com/photos/juniorvelo/2563696058/in/set-72057594113044440/, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=5088313
Middle One and Two and Bottom
By Davefoc – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6973668
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