In addition to being a constant source of irritation, they can also carry pinkeye and eyeworms. Young animals are highly susceptible to pinkeye and the results of this disease can lower the market value of affected animals. Insects that have the piercing sucking type of mouth parts include horn flies, stable flies, deerflies and horse flies . These insects pierce the animal's skin and suck its blood. The most common of these types is the horn fly which was introduced from Europe in about 1890.
Horn flies feed mainly on cattle but also attack sheep, goats, horses, swine and other animals.
Horn flies congregate around the ears, flanks, withers, back and belly. Horse flies are another common blood sucking fly that annoys cattle. Under high fly populations, the average daily loss of blood from an animal can be as high as 100 ml. These flies are also capable of carrying and transmitting anaplasmosis and anthrax. The life cycle of this type of fly is interesting as the eggs are not laid in manure.