An arachnid is a type of animal with eight legs, two main body parts, and no antennae or wings. Spiders are the most famous arachnids, but the group also includes scorpions, ticks, mites, and harvestmen (also called daddy longlegs).

What makes arachnids different from insects? Insects have six legs and three body sections, while arachnids have eight legs and two body sections. Insects often have antennae and wings, but arachnids never do. A spider crawling across your wall is an arachnid. A beetle scurrying beside it is an insect.

Many people feel uneasy around arachnids, especially spiders, but most species are harmless to humans and actually helpful. Spiders eat enormous quantities of mosquitoes, flies, and other pests. Some arachnids, like certain mites, are so tiny you need a microscope to see them. Others, like tarantulas, can be as big as your hand.

Arachnids have been around for about 400 million years, far longer than dinosaurs. They've survived and thrived by adapting to almost every environment on Earth, from deserts to rainforests. Scientists have identified over 100,000 species of arachnids, and they estimate that thousands more remain undiscovered.