Bunostomum species are nematodes of the small intestine of ruminants and camelids. Important species include: B. phlebotomum in calves and B. trigonocephalum in lambs. The worms are stout and measure 1–3 centimetres (0.4–1.2 in) in length. Young animals are most commonly affected and only several hundred worms are necessary to cause morbidity. Adults often carry worms without showing clinical signs.