An order of arachnids, the tailed whip scorpions, comprising about 70 species from tropical and warm temperate Asia and the Americas. Most are dark reddish-brown, of medium to giant size, 0.72–2.6 in. (18–65 mm), the largest one being Mastigoproctus giganteus of the southern United States and Mexico. The elongate, flattened body bears in front a pair of greatly thickened, raptorial pedipalps set with many sharp spines and used to hold and crush insect prey. The first pair of legs is elongated and modified into feelers. The abdomen terminates in a slender, many jointed, whiplike flagellum. The uropygids are harmless, nocturnal creatures without poison glands that live in dark places and burrow into the soil. When disturbed, they expel a volatile liquid, with the strong odor of acetic acid, from a gland at the base of the tail. This accounts for the name “vinegaroon” given by many Americans to these much-feared animals.