Haematobia irritans

Haematobia irritans, the horn fly, is a small fly (about half the size of a common housefly) described by Linnaeus in 1758. It is of the genus Haematobia which is the European genus of bloodsucking flies. Haematobia irritans is a native of Europe but has been introduced to North America and is considered a potentially dangerous livestock pest. H. irritans is the smallest of the biting muscids, gray in color, approximately ​3⁄16 in (4.0 mm) in length. Both the male and female have slender, black, piercing mouthparts which project forward from the bottom of the head. They often aggregate densely on cattle, each fly oriented with its head in the same direction as hair tips of that site on the host. Horn flies typically have eyes that are dark reddish brown. The horn fly lays eggs in fresh cow manure, and the female is known to lay her eggs in the feces before the cow has even completed defecation. The larvae remain in fresh pats of the animal's dung and feed on both the resident bacterium and the compositions of the decomposition products of the resident bacterium. The adult will finds a suitable host and remains on it and others in the same herd for life, with the female only leaving to lay her eggs. Horn flies will also move around to different areas on the same animal to regulate their temperature and minimize their exposure to the wind. Both the male and the female subsist completely on blood, using their sharp mouthparts to pierce the animal's hide to suck it out.