Deer Fly

Deer Fly!

Deer flies are often mistaken for Horse fly’s, but these flies do not get as large as Horse Flies do. Deer flies are also known as Yellow Flies. They usually have distinctive patterned yellow or green eyes. Deer flies can reach up to a 1 inch in length.

The female Deer fly feeds on blood while the male feeds on nectar. (I can see a pattern here. Can you?) She needs the blood for it’s protein so she can lay eggs. A farmer in KY reported last year that his cattle lost 100 lbs (per animal) from the disease Tabanids, which is transmitted by horse and deer flies. It is not uncommon to see as many as 100 flies feeding on an animal at one time. Twenty to thirty flies feeding for six hours are capable of taking 100 cc of blood. Deer flies track their “prey” by sight and movement and also carbon dioxide output.

Eggs mass has been found as early as May 5th and as late October 13th. Most have a year-long life cycle but some larger species may take two or three years. Adult life span is 30 to 60 days.

Eggs are laid in masses ranging from 100 to 1000 eggs. Eggs are laid in layers on a vertical surface such as overhanging foliage, projecting rocks, sticks and aquatic vegetation. Aquatic vegetation is most preferred. A shiny or chalky secretion, which aids in water protection, often covers eggs. The vertical surfaces on which the eggs are deposited are always directly over water and wet ground favorable to the development of larvae. The female will not deposit egg masses on vegetation that is too dense. Eggs are initially a creamy white color but soon darken to gray and black. Eggs are cylindrical in shape and measure from 1 to 2.5 mm in length. Eggs hatch in five to seven days, depending upon ambient weather conditions, and the larvae fall to the moist soil and water below.

Their bite is the same as the Black Fly and Horse Fly. The Deer fly uses a knife like mouth parts to inflict a wound then the fly licks it up. For humans the bite is often painful and itchy. Wearing long-sleeves and pants and using repellant can help in avoiding bites. For livestock there are traps available, but repellants seldom work.