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 study used two calculation methods based on different models, and they gave consistent results. The researchers said all people together eat about 400 million tons of meat and fish a year. 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.

As of November 2026, the World Spider Catalog lists 54,250 species of spiders in 139 families. Over 250 species of wolf spiders live in the United States and Canada, and wolf spiders are beneficial predators in several different ecosystems. Not every spider builds a web, and about half of spiders create webs not for capturing prey but as hiding places. Wolf spiders are unique among their kin in that they are not web-builders, and unlike most spiders, they have excellent vision that is used for prey capture. Crab spiders wait among flowers for prey to visit and do not wrap their prey with silk.

Spiders were among the earliest animals to live on land, probably evolving about 400 million years ago. 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 the animals first thought to be the oldest spiders were more primitive than spiders in many ways, and Shear said they may be spider ancestors. Amber fossils show that a spider fauna basically similar to that of the present day existed more than 30 million years ago. Selden said these pre-spiders (Uraraneida) existed for more than 100 million years, living alongside real spiders, and that their spigots probably helped line burrows and make homing trails but could not make webs.

A house, like any other house, contains 10 to 30 kinds of spiders, not just one, and house spiders could not survive without insect prey. Spiders in sinks and bathtubs come down the walls, attracted by water, and they cannot come up through the drains. Contrary to urban legend, spiders are not able to lay their eggs inside the skins of ripe banana fruit, and daddy-long-legs, also called harvestmen, are not spiders, and most spiders are harmless to people, and spiders very rarely bite people. A spider is an arachnid, not an insect. Leave wild spiders alone, and tell a grown-up if you find one.

Words to know

• species: kind of animal
• prey: hunted animals
• ecosystems: living communities
• Uraraneida: pre-spiders