Myth: "Eight legs" always means "spider"

October 23, 2015
Rod Crawford

Myth: You can always tell a spider because it has eight legs.

Fact: Not exactly. Scorpions, harvestmen, ticks, and in fact all arachnids—not just spiders—have four pairs of legs (see illustrations). Insects have three pairs. Also, notice that I said "four pairs" instead of "eight." The number of leg pairs (one pair per leg-bearing segment) is more significant than individual legs, which can be lost.

 

Examples of 6 of the 11 orders of arachnids. All have eight legs. Only one is a spider.

Spider illustration

A spider, Missulena occatoria (Australia).

Whipscorpion illustration

A whipscorpion, Abaliella dicranotarsalis.

scorpion illustration

A scorpion, Charmus indicus (India).

pseudoscorpion illustration

A pseudoscorpion, Chelifer tuberculatus (Algeria).

harvestman illustration

A harvestman, Phalangium opilio (worldwide).

Solpugid illustration

A solpugid, Ammotrechella cubae (Cuba).

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