Haematobia irritans, the horn fly, is a small fly (about half the size of a common housefly). It was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae. 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.