Spiders may not have what some men crassly refer to as their third leg, but they can’t get by without the real thing. New research reveals that, without a third set of legs, the male road tarantula (Eupalaestrus weijenberghi) can’t score a mate. The hairy South American spiders use their legs to create vibrations that can be irresistible to females, which live for a decade in contrast to his 60-day lifespan. But it turns out that all of his eight legs aren’t created equal. The third pair from the front is key to completing courtship, apparently because it is perfectly positioned to produce critical vibrations, researchers report in the August issue of the Journal of Arachnology. When they immobilized his third pair by tying it up with a bit of thread, she just wasn’t interested. The bondage experiment marks the first time that scientists have been able to document this leg of the tarantula’s sex life, they note.