Face Fly

Musca autumnalis — the face fly — is one of about 60 species in genus Musca (which also includes the house fly M. domestica) and one of the most consequential cattle face-feeding pests in temperate North America. The species is native to Eurasia and was accidentally introduced to Nova Scotia, Canada in 1952 in shipping cargo; it has since spread across the entire eastern, central, and northern US and southern Canada. Adults are 5-7 mm long, dark gray with four black thoracic stripes — virtually indistinguishable from the closely related house fly except by careful examination of the male reproductive structures. The species' defining ecological behavior is the FACE-FEEDING habit. Adult flies aggregate on the faces of cattle (and other large grazing mammals — horses, deer, etc.) and feed on tears from the eye, mucus from the nostrils, and saliva from the mouth. The flies use sponge-like labellar mouthparts to lap up these secretions; they do not bite or pierce the skin. The face-feeding causes major irritation to cattle (a single cow may have 100+ face flies on her at any time during peak summer), reduces grazing time, and is associated with significant weight loss and reduced milk production in dairy cattle. The species' more consequential biological role is as the primary vector of MORAXELLA BOVIS — the bacterium that causes infectious bovine keratoconjunctivitis (IBK, commonly called 'cattle pinkeye'). Face flies pick up the bacteria from the eye secretions of infected cattle and transfer them to uninfected cattle during subsequent feeding visits. Pinkeye causes corneal ulceration, weight loss, and (in severe cases) blindness. The disease is one of the most economically significant bovine bacterial diseases in temperate dairy and beef cattle worldwide. Like cluster flies, face flies are also major autumn 'cluster' pests of rural homes — overwintering adults aggregate in attics, wall voids, and unused upper rooms by the thousands, emerging into living spaces on warm winter and spring days. The species is a continuing concern in both veterinary medicine and rural residential pest management.