Insect and related parasites cause direct and indirect damage to horses. They feed on the horses; cause irritation; spread diseases; and cause digestive upsets, poor condition and retarded growth. Therefore, strong parasite control programs are needed.
Many different flies are pests of horses. Basically, they may be divided into three groups by their feeding habits. Sponging mouthparts, found on house flies and face flies, are used to sponge or sop up liquid foods. Stable flies, horn flies, horse flies and mosquitoes use piercing mouthparts to pierce the host animal's skin so that they may feed on blood. Some flies, such as bots and cattle grubs, have no mouthparts as adults.
"PB1478-Horse Pest Management," The University of Tennessee Agricultural Extension Service, PB1478-2M-5/93 R12-1040-18-004-93, http://trace.tennessee.edu/utk_agexani/13