Why do spiders have 8 legs and not 6 or 4 instead?
Excellent question! The earliest arthropods we know of had bodies made up of a series of segments, some of which had a pair of legs each. If you look at a centipede, for instance, that sort of body plan is still around. For various reasons (most of which we don’t know, and some of which we can only guess at) certain groups within the arthropods settled on a certain number of body segments and number of legs. Some of those legs became very specialized sensory organs (antennae), some became “holders” (pedipalps or palps), some became claws, etc. Spiders have only 2 body parts, the abdomen and the fused cephalothorax (head and middle region merged together). The middle region (thorax) is the fused leg-bearing remains of the multiple segments of earlier arthropods, and in spiders it has only 8 legs left. In addition, spiders have 2 pedipalps up near the front of the body, which help them manipulate food (or if they’re male spiders, which serve as sexual organs). Spiders don’t have speciali
