Scorpions are any arachnid of the order Scorpionida. Unlike the majority of arachnid species, scorpions are viviparous. The young are born one by one, and the brood is carried about on its mother's back until the young have undergone at least one moult. All known Scorpion species possess poison or venom. Scorpions use their venom to kill or paralyze their prey so that it can be eaten; in general it is fast-acting, allowing for effective prey capture.