As of November 2026, the World Spider Catalog lists 54,250 species of spiders in 139 families. A spider has eight legs and two body parts, while an insect has three body parts, so a spider is not an insect, and most spiders have eight eyes, though some have fewer. Daddy-long-legs, also called harvestmen, are not spiders, and they cannot make silk. Most spiders are harmless to people, and spiders very rarely bite people. Leave wild spiders alone, and tell a grown-up if you find one. A house, like any other house, contains 10 to 30 kinds of spiders, not just one.
Spiders do not have ears, and they do not hear in the way humans do; instead, they hear with hairs on their body that are sensitive to touch and vibration. Spiders rely on touch, vibration and taste to navigate and find their prey. A jumping spider's front pair of eyes is very large, and it has another three pairs of smaller eyes in three rows, so that together the four pairs of eyes cover virtually the entire 360 degrees, although a jumping spider's eyes cannot adjust their focus. Unlike most spiders, wolf spiders have excellent vision that is used for prey capture, and one cave species of spider, Sinopoda scurion, has lost its eyes altogether.
Spiders do not move their legs the way mammals do by pairing opposing muscles; they use hydraulics, and a chamber near the head contracts to send blood to the legs, forcing them to extend. Jumping spiders use their third and fourth pairs of legs for jumping and seize prey with their front pair of legs, and when they move or jump, they always leave a safety line of silk, or dragline, behind. If a jump misses, a spider can climb back to its original position. A spider's body is covered with a rigid exoskeleton.
Spiders moult to grow: a new larger cuticle is made underneath the old one, which splits and the spider climbs out. If a spider loses a leg, it can still walk and cling to surfaces, and a young spider with at least one more molt to go will regenerate its leg. Females weave silk egg sacs, which may contain hundreds of eggs, and after hatching, spiderlings use their fangs to cut a hole in the sac and emerge. Spiders may have to go for long periods without eating if food is scarce, and males of most spider species have short life spans and survive only a few matings. Some spiders make noises to attract mates or as warning signals.
Spiders use silk to protect their young, catch food, make homes and move around, and ten different types of silk glands and their spigots are known in spiders, with up to eight silk glands present in a single species, each producing silk with different properties and uses. Silk starts as a liquid stored in internal silk glands and hardens into a solid form before the spider uses it, and a spider's silk line is typically only about 0.001 mm to 0.004 mm thick. The tensile strength of dragline silk is greater than that of mild steel and almost all artificial fibres, though Kevlar is an exception, and a strand of spider silk is five times stronger than a steel cable of the same weight, said Hannes Schniepp of William & Mary.
Silk gets its stretchiness from loose, coil-like protein chains and its stiffness and strength from highly ordered protein crystals. Most spider silks are cylindrical, like a rope, but recluse spiders make a flat, ribbon-like silk that works more like a cable, and researchers at William & Mary built a model of recluse spider silk with seven levels of structure. They found that a single nanofibril inside the silk is about 10,000 times smaller than a human hair. Cribellate silk tangles the bristles, spines and claws of insect prey, while sticky silk is a glue-like liquid carried on fibrous support lines, such as the spiral line of an orb web.
Orb webs all follow the same general pattern: a spider begins with a disorganized protoweb and replaces it with the frames, spokes and hub of the final web. In a 2021 study of a species of tiny spiders that spin webs at night, scientists showed that web making follows rules that were the same for every spider, and the researchers hope next to learn how these stages are encoded in the spider's brain. An orb weaver lays a non-sticky temporary spiral first, starting from the centre and running outwards, and it removes and rolls up that spiral as it lays down the sticky spiral. The excess silk is eaten and recycled, and it takes about 30 to 45 minutes to make the web.
Spiders were among the earliest animals to live on land, probably evolving about 400 million years ago, and fossils from the Devonian Period, about 380 million years ago and more than 150 million years before the dinosaurs, were long thought to be the oldest spiders. Paul Selden and William Shear found that these animals were more primitive than spiders in many ways, and fossil animals called Attercopus wove broad sheets of silk from spigots on plates on the underside of the body. Unlike spiders, they had long tails. Spiders have been around for eons, but there are few fossil records because their soft bodies easily deteriorate.
A 2017 study estimated that all the spiders in the world together eat 400 to 800 million metric tons of prey a year, and more than 90 percent of it is insects and springtails. The researchers said all people together eat about 400 million tons of meat and fish a year. The study used two calculation methods based on different models, and they gave consistent results, and Martin Nyffeler of the University of Basel said the calculations let scientists measure for the first time on a global scale that spiders are major natural enemies of insects.
Words to know
- hydraulics: fluid power
- exoskeleton: outer shell
- protoweb: first rough web
- dragline: safety thread
- nanofibril: tiny fiber
