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Public health & wellbeing > Disaster management

Black flies - a public health risk after a flood

The number of black flies (Austrosimulium) can increase following a flood or heavy rain, particularly in inland areas. While black flies do not transmit disease, allergic reactions and bacterial skin infections may occur from bites and scratching the bites.

Black flies are aggressive biters that are found in areas around streams and rivers. They breed in running water–but once flood water recedes the number of black flies rapidly decrease. Black flies are active only during the day and do not bite at night. Their peak activity period tends to occur from sunrise to mid-morning (10 am) and late afternoon (4 pm) to sunset.

Female black flies are blood feeders—its bites can itch and persist for several days. Anticoagulants—a blood thinners that stop the blood from clotting—injected into the bite site by black flies can cause allergic reactions in sensitive individuals.

Signs and symptoms

The range of signs and symptoms associated with bites can include:


Black fly bites should be managed to prevent secondary skin infections: 


Black fly bites can be avoided by:

It is recommended: 

Further information

Last Updated: 14 December 2015
Last Reviewed: 28 October 2013

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