How many legs does a spider have?

Spiders have eight legs, and the count is not a detail but a defining feature of arachnids, the group that also includes scorpions, ticks and mites. Insects have six, and the difference goes deeper than a pair of limbs: an insect body divides into head, thorax and abdomen and usually carries antennae and often wings, while an arachnid fuses head and thorax into a single cephalothorax, has no antennae and never has wings. All eight of a spider's legs attach to that front section. Spiders also have two extra pairs of appendages that are not legs, the fangs and the pedipalps, which are used for handling prey and, in males, for mating. Their legs work by an unusual hybrid mechanism: muscles pull them in, but extending them relies partly on hydraulic pressure of body fluid, which is why a dead spider curls up as pressure is lost.

Not all spiders build webs; many hunt actively or ambush prey, and silk is used for egg sacs and drag lines regardless.