I was about ten years old when a horse fly bit me. I was on a camping trip. I saw the giant fly land on my leg. It went to work immediately. Before I even had a chance to brush it off, it ripped into my skin. The pain was far more intense than a bee sting. I slapped it off. A rivulet of blood flowed down my leg.
Like mosquitoes, horse flies subsist on a diet of blood. But rather than piercing skin with a needle-like proboscis like mosquitoes, horse flies use scissor-like mouth parts to slash the skin of the unlucky host. They then secrete an anticoagulant into the cut to thin the blood lap up the blood that pools in the wound with a sponge-like tongue.
What makes horse flies particularly menacing is their dogged determination in pursuing their prey — they will return again and again until they either secure their blood meal or are killed. They'll track their target relentlessly, circling and attacking repeatedly from different angles. Scientists have filmed horseflies executing complex flight maneuvers similar to fighter jets, including the Immelmann turn. Their aggressive pursuit can drive livestock to the point of panic, sending cattle rushing to seek shelter in water or shaded areas to escape the onslaught.
They can reach astounding speeds — the male Hybomitra hinei wrighti has been recorded flying at up to 90 mph when pursuing a female.
Even more unnerving is their strategic approach — they often target areas of the body that are difficult to defend, such as the back of the neck or legs, and will follow their prey for considerable distances.
The ancient Greek playwright Aeschylus's observation about horse flies in Prometheus Bound is as relevant today as it was in the 4th century BC: "Ah! Hah! Again the prick, the stab of gadfly-sting! O earth, earth, hide, the hollow shape—Argus—that evil thing—the hundred-eyed."
Previously:
• Mutant fruit flies created by radiation, would take over Earth within months
• A toilet in the shape of a fly