Are you being bugged by Buffalo Gnats?
Yvette Johnson DVM
Ken Koelkebeck PhD
Recently several areas in Illinois have reported large numbers of black flies have been biting
poultry, pets, livestock, and people. Several poultry have died as a result of these attacks and
more than 40 people have sought medical attention.
FAQs about Buffalo Gnats or Black Flies
What are they?
Buffalo gnats or black flies are blood sucking flies of the Simuliidae family. The females may
attack people and animals in an effort to have a blood meal for egg production.
Do they pose a public health risk?
In humans their bites typically cause pain, itching, and swelling. However, those who have an
allergic reaction may have more serious complications.
Will they harm my animals?
The consequences for animals can be more severe. Livestock and poultry are sometimes killed by
the flies when bitten by large numbers of them. Death can be due to anaphylactic shock, toxemia,
blood loss, or suffocation when the flies are inhaled. Some species of black flies can transmit a
blood-borne parasite that affects poultry called, leukocytozoon.
When can I expect them to be a problem?
The adults emerge in the late spring to early summer and are known to travel more than 10 miles
in search of a meal. The larvae are very sensitive to water temperature. Once the water
temperature reaches 66 - 75 degrees F the larvae will die and the buffalo gnat season is over until
next year.
Why are they causing problems now?
The eggs are laid in running water and the larvae are filter feeders. They are sensitive to
sediment, toxins, and low oxygen levels in the water. With adequate rainfall and as surface water
quality improves the conditions are more favorable for the flies.
How can I protect myself from them?
Black flies are outdoor, daytime feeders so the best protection is avoidance. If you must be
outside, light colors and long sleeves are recommended. Permethrin treated clothing and insect
repellants containing DEET have been used with limited success.
How can I protect my animals from them?
Animals that are housed indoors are at a much lower risk of being bitten even if the building is not
fly-proof. It is recommended that poultry be kept indoors in a darkened barn during the day.
Usually fans or some means of cooling are needed. Permethrin-based fly control products are
recommended for livestock and poultry.
For more information see the following references:
2007 Agricultural Pest Management Handbook
www.ento.okstate.edu/ddd/insects/blackflies.htm
www.cnn.com/2007/US/05/11/gnat.ap/index.html?eref=rss_us
www.fws.gov/whiteriver/nastygnats.htm
www.ext.colostate.edu/pubs/insect/05582.html
http://insects.tamu.edu/extension/bulletins/uc/uc-019.html
http://webextension.uiuc.edu/greene/news/news6445.html