Yellow Flies

Facts, Identification, & Control

Scientific Name

Diachlorus ferrugatus


What Do They Look Like?

Photo of Yellow Fly
Yellow Fly image licensed under CC

  • Size: Adult yellow flies are primarily about 3/8 inches long. Larvae grow to about 1/2 inch long.
  • Color: The adult body is yellow, their front legs are mostly black, and the other two pairs of legs are yellow. They have large eyes that are blue-green with two purple bands. Larvae have fine yellowish-brown short hairs on their whitish-colored body.
  • Characteristics: These flies have wings that are clear, but they have black and yellow veins with prominent brown patches toward the middle and rear of the wings. Larvae are slender and aquatic or semi-aquatic. Adults look similar in appearance to deer flies.

How Did I Get Yellow Flies?

Yellow flies do not readily enter homes, they are frequently in areas around water sources like pools and ponds. Homeowners with standing water in their yards are more likely to encounter these flies. These flies typically bother residents in late summer and early fall. Avoiding direct sunlight, these pests appear in large numbers on cloudy days and during the late afternoon.

How Serious Are Yellow Flies?

Female yellow flies inflict a painful bite that can create a swollen and itchy welt. This may lead to infection if the bite is not kept clean and dosed with a medical skin ointment. It is hard to prevent these bites because these pests travel quickly and attack any exposed skin.

Since they inject anticoagulant-containing saliva during blood feeding, some life-threatening reactions may occur in people that are highly allergic to the anticoagulant compounds.

Bite Symptoms
Symptoms of yellow fly bites include:

  • Itching
  • Red areas
  • Swelling

Signs Of Infestation

The most obvious signs of a yellow fly infestation is their bothersome and painful bite and the symptoms associated with it.

How Do I Get Rid of Yellow Flies?

What You Can Do
Things you can do to prevent or control yellow flies include:

  • Wear clothing that covers skin
  • Repellents
  • Traps

What Orkin Does
Your local Orkin technician is trained to help manage yellow flies and similar pests. Since every building or home is different, your Orkin technician will design a unique program for your situation.

Orkin can provide the right solution to keep yellow flies in their place and out of your home or business.

Behavior, Diet, & Habit

Yellow flies are members of the Tabanidae family that also includes horse flies and deer flies. These flies are one of the few species of this family that will assault hosts indoors.

What Do They Eat?
Like mosquitoes, the female consumes blood while the males do not bite and are mainly pollen and nectar feeders. Yellow flies are strong fliers, and females may travel long distances in search of blood meals.

Where Do They Live
Adult yellow flies tend to live around yards and bodies of water. In Florida, field researchers have found their larvae in shaded areas in:

  • Beneath the water surface
  • Root mats of cypress
  • Shingle oak
  • Wood plants

Geographical Range
Diachlorus ferrugatus are found in the southeastern U.S. from New Jersey to Texas, as well as in the Bahamas and from Mexico to Costa Rica. The only species found in the U.S., Diachlorus ferrugatus are thought to have traveled to the states from Mexico.

Peak activity season in Florida and much of the pest’s southern distribution is April through June, but they may become problematic anytime from early spring through late fall.

Life Cycle

Yellow flies undergo complete metamorphosis, meaning their life cycle involves four stages: the egg, larva, pupa and adult stage.

Yellow fly eggs are small, about 1 1/2 millimeters. They are white when laid by the female, but turn black several hours after being deposited. Egg masses are commonly mistaken for feces or specks of tar. After 5 – 12 days, these eggs hatch and the young larvae drop into the water or mud and begin feeding.

Females produce egg masses on water or other materials surrounding water including:

  • Plants
  • Rocks
  • Sticks

Larvae & Pupae
As larvae, yellow flies feed on decaying organic substances and molt about 10 times before pupating. Once mature, larvae will migrate to drier soil conditions and develop into non-feeding pupae.

Mating takes place soon after adults emerge from the pupal stage. These pests breed prolifically when near large bodies of water. Depending on the species and environmental conditions, there are only one or sometimes two generations per year.