If you’ve ever been in back-yards, farm areas, or wooded areas and had a large fly land on you that proceeded to bite the living daylights out of you, you’ve probably become acquainted with the yellow fly – also known as a horse fly.

Yellow Fly (Horse Fly) Appearance

The life cycle of the yellow fly is in four stages:

1.       The egg

2.       The larva

3.       The pupa

4.       The adult

The adult horse fly is around 3/8 inches long and is primarily yellow – hence the name yellow fly. They look very similar to deer flies. The body is yellow, as are all the legs, except for the front two which are mostly black. The wings have yellow and black veins running through them, but are otherwise clear except for a brown patch on the rear middle portion. The eyes of the yellow fly are large and green/blue with two bands of purple.

The eggs of the yellow fly are very small, only about one and a half millimeters. When the female first lays them, they are white, but within a few hours they turn black. People often mistake yellow fly eggs for specks of dirt or tar or for feces. The larvae are around a half an inch long, are slender, and white or milky colored, covered with very fine brown-yellowish short hairs.

Habit, Diet, and Behavior of the Yellow Fly (Horse Fly)

At the larval stage, the yellow fly feeds on organic substances at varying stages of decay. They tend to prefer shaded areas where food is abundant, typically around wood plants and under the surface of the water. Before pupating, they typically molt around 10 times. Once they are mature, they will develop into pupae that are basically non-feeding and move to an area with drier conditions.

Like the mosquito, the adult female horse fly bites and seeks out blood meals. Conversely, the males feed on pollen and nectar and don’t bite. The female is a vicious biter and deer fly bites can become swollen, red, itchy, and painful. For the most part the adult flies remain near the larval breeding site, but being the strong fliers that they are, the females can travel quite far when seeking out a blood meal.

Symptoms of a Yellow Fly (Horse Fly) Bite

The first symptom of a horse fly bite is that it hurts like the dickens! Other symptoms include:

·         Red, itchy, swollen area surrounding the bite

·         Itchy skin is a primary symptom of yellow fly bites. Secondary bacterial infections can crop up from this if the bite is not disinfected and kept clean.

·         In rare cases, some people may have severe allergic or life threatening reactions to the yellow fly’s anticoagulant containing saliva that is used during blood feeding.

You are most likely to encounter yellow flies near large bodies of water, which is their breeding ground, but they are also often found around wooded areas.

Reproduction of the Yellow Fly

When adult yellow flies emerge from the pupal stage they almost immediately mate. Females will hide their egg masses near water on sticks, rocks, plants, and other items. The eggs hatch in 5 to 12 days and the larvae drop into the mud or water. They begin feeding. There are typically just one or two generations over the course of a year, but this depends on the species and the environment.

How to Remove Yellow Flies From Your Yard

The Fly Cage horse fly trap is specifically designed for Horse flies, Deer flies, Yellow flies, and Green heads. Horse flies, Deer flies, Yellow flies, and Green heads, are attracted to CO2 and heat, which is why they are attracted to humans.  These types of biting flies are also visual hunters.  The Fly Cage biting fly trap utilizes visual motion to attract the flies by suspending the black lure below the cage.  Biting flies go straight to the target flying upward into the cage and once caught, dehydrate.

Learn more about how the Fly Cage works here.