A to Z of Pests

Horse Fly

Family Tabanidae

Appearance

• Adults can be up to 25 mm long.
• 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.
• A horse–fly’s bite can be very painful. Unlike insects that pierce the skin, horse–flies have mouth parts that work like miniature knives, which they use to slash open the skin with a scissor–like motion.

Lifecycle

• 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.

Habits

• 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.
• The males are mainly pollen and nectar feeders.
• Tabanids are most active during daylight hours.
• As with mosquitoes, it is the female fly that is responsible for biting.
• Relentless attacks on livestock can result in reduced weight gain.