Fly IdentificationAdult Horse flies can be up to 25 mm long. They are black to dark brown in colour with green or black eyes. The males have contiguous eyes, which easily differentiates them from females where the eyes are widely separated.
DescriptionHorse flies are a particular pest to livestock. Relentless biting attacks by females can result in reduced weight gain in some animals. Male horse flies are mainly pollen and nectar feeders and are most active during daylight hours. Horse fly bites can be very painful for humans too.They have mouth parts that work like miniature knives, which they use to slash open the skin with a scissor–like motion. Mating is initiated in the air and completed on the ground where the female then deposits an egg mass sometimes with a shiny or chalky secretion, which aids in water protection. Eggs are laid in masses ranging from 100 to 1000 eggs on a vertical surface overhanging water or wet ground favourable to larvae development. The eggs hatch in 5–7 days. They overwinter in the larval stage and pupate during the spring and early summer. Adult life cycle is 30 to 60 days.