Black widow spiders are a group of spiders which are renowned as some of the most dangerous types of spiders in the world, due to their very large venom glands. There are many types of black widow spiders, including the Southern black widow, European black widow, Northern black widow, and Western black widow. These are widely distributed across the globe, occurring on every continent except Antarctica. They prefer warm climates and can be found in the warmer regions of the United States and Canada, most notably the Okanagan Valley in British Columbia. Due to their penchant for warmth, these spiders will often find their way into homes as they search for a cozy climate during winter. This is the time when people are most at risk of finding a black widow spider.
Bites from a black widow spider are usually very painful, due to the sheer amount of venom they expel. Their venom contains latrotoxin, which causes symptoms in humans, such as sweating, vomiting, and rigid muscles. A bite from a black widow spider may require medical attention, but it is very rarely fatal, in spite of their reputation. Although these spiders inspire fear in many people, they are actually known to have a timid nature when it comes to humans. They are not aggressive and will not seek to bite humans unless they perceive that they are in danger. Some studies also suggest that they bite fingers because they have very poor vision, and they mistake human fingers for prey.
These spiders make incredible webs, with silk that is known to be stronger than steel. They make elaborate webs to trap their prey, and then inject them with venom to kill them and prevent them from escaping. They rely on vibrations to signal to them when a creature has visited their web, due to their poor vision. Their diet mostly consists of beetles, insects, and other spiders. They aren't terribly fussy about what they eat, but they do like to maintain a clean web, so they thoroughly clean their web after capture and feeding, or spin a new one.
Black widow spiders are usually easy to identify. The females are entirely black in color, except for red or orange markings on their backs. The male is also black, with similar markings, but in yellow. The females are the largest of the two, usually at double the size of the males, and it is the females who present the biggest danger to humans. For this reason, if you ever encounter a black spider with red markings, you should regard it with caution, in case it is a female black widow spider.
They also present a certain amount of danger to their fellow males, as they are sometimes known to kill the male black widow after mating. The cause of this is uncertain, and nobody really knows why this sometimes does and sometimes does not happen, though it is suggested that sexual cannibalism is a means of ensuring the survival of their young. In order to avoid death, male black widow spiders select their mates based on whether they have already recently eaten, to increase their chances of not being eaten themselves. This unusual behavior is where the name 'widow spider' comes from.