Annoyance factor: 7
Favorite hangouts: Streams, rivers and other bodies of water.
Most annoying when: You've finally gotten around to taking the boat out and are trying to enjoy a peaceful day on the lake.
Annoying, associated diseases and afflictions: Onchocerciasis ("river blindness"), mansonellosis, severe swelling and itching around bite area, an allergic reaction known as "black fly fever" which includes headache, nausea and swelling of the lymph nodes.
Repulsive eating habits: Also known as buffalo gnats, the supremely vexing blood-sucking flies known as black flies prefer to attack — and feed from with blade-like, skin-slashing mouthparts — a human host's head area around the eyes, ears and scalp. Why? They're attracted to the carbon dioxide in your breath. Like mosquitoes, it's primarily female black flies that do most of the biting. Unlike mosquitoes, black flies bite only during the day.