There are more than 50,000 known species of spider, but the world's deadliest spiders are few. All spiders can bite and inject venom, but their fangs are best suited for biting and stunning insects. When spiders do bite humans, they don’t always inject venom, and most bites cause no dangerous reaction.
When it comes to human fatalities, only a few arachnids may be classified as the world's deadliest spiders. Bites from black widow, brown recluse and Brazilian wandering spiders have been known to kill a small child or fragile adult now and then, but death by spider bite is not very common outside of deep jungle areas. A delay in medical attention often tips the scales in case of a fatal spider bite. Antivenin, when available, can be quite effective.
Identifying poisonous spiders can be difficult, but each has its own particular characteristics. Perhaps the most familiar is the black widow, an arachnid native to North America. They are very small, ranging from a half-inch to an inch (1.27 to 2.54 cm) in length, including legs. Black widows are completely black except for a large red or orange hourglass design on the underside of the abdomen. The trick is turning the spider over to inspect its belly. Black widow bites are seldom venomous, but symptoms of a poison bite include muscle cramps and pain at the wound site.
Another venomous North American spider is known as the brown recluse, sometimes called a fiddleback spider. It is usually brown or light brown with a mark looking somewhat like a violin faintly visible along its back. At less than an inch (2.54 cm) in length, the brown recluse often hides out in woodpiles and quiet corners of a basement or garage. Bites are rare, and necrosis of the bite wound is even rarer. A very small number of people can have a systemic reaction to a brown recluse bite. Fatalities are usually young children or people with weak immune systems.
The world's deadliest spiders to humans are Brazilian wandering spiders, also known as banana spiders. More people in the world die from their venom than any other poisonous spider on the globe. The Brazilian wandering spider is native to the jungles of South and Central America, and has a tendency to wander into populated areas, hence its name. Venomous banana spiders grow quite large, with a leg span reaching four to five inches (10.16 to 12.7 cm). When attacked, the spider will rear up on its hind legs and sway back and forth in an aggressive stance.
Tarantulas are often thought to be one of the world's deadliest spiders, but that is simply a myth. Tarantula spiders can grow to a huge size, with leg spans ranging between 3 and 12 inches (7.62 and 30.48 cm). They are also quite fat and hairy, giving the tarantula a fearsome appearance; however, tarantulas are relatively docile and rarely bite. Although no human has ever died directly from tarantula venom, a bite wound can become infected if not properly treated.
Lastly, the lowly insect known as a daddy long legs is definitely not one of the world's deadliest spiders. It’s not even really a spider. The daddy long legs has a set of tiny fangs that cannot bite through human skin. They do have claws on the end of their legs that can pinch, but daddy long legs are considered completely harmless.