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Yellow-Fly (Diachlorus ferrugatus)

Detailing the physical features, habits, territorial reach and other identifying qualities of the Yellow-Fly

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Image Credit: Judy Gallagher (Creative Commons)
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The bites of the female Yellow Fly are both annoying and painful, especially since they attack at random and usually have their friends with them.

Updated: 07/15/2021; Authored By Staff Writer; Content ©www.InsectIdentification.org
Sometimes mistaken for a Deer Fly, Yellow Flies are just as unwelcome by both humans and animals. The female attacks exposed flesh for a quick blood meal. Males do not bite. Heads and ears are easy targets on humans. Faces, backs, and legs are often targets on animals such as horses and livestock. These large animals use their tails to swat and kill the Yellow Fly since repeated attempts to bite are normal. The fly bite is painful, becoming red and irritated over the next day or two, often ending in an allergic reaction that can lead to painful blisters. Humans can use insect repellents with DEET to deter them. Fly traps in stables and barns are said to reduce their numbers in those areas, sparing livestock.

Both male and female Yellow Flies drink flower nectar and eat pollen, but females add to their diet by consuming blood from animals. She can lay 50 or so fertilized eggs in a muddy area, near a lake, creek, pond, or stream. Larvae (maggots) hatch and molt several times before taking on a winged adult form. They feed on decaying matter and spend some time feeding on debris in water before migrating to land.

The most active months for biting are May and June in the southern states. The fly is most active between afternoon and dusk. Large congregations of them typically live near water, which is necessary for part of the larval life stage. They are often found bothering people and animals in backyards, open fields, parks, farms, and forest edges near water.

General Characteristics
Capability, Shape, Texture/Pattern, Benefits, Dangers
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Flying insect icon
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Taxonomic Hierarchy
Species Breakdown
Kingdom: Animalia
  Phylum: Arthropoda
    Class: Insecta
      Order: Diptera
        Family: Tabanidae
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          Genus: Diachlorus
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            Species: ferrugatus
Identifying Information
Size, Colors, Features
Scientific Name: Diachlorus ferrugatus
Category: Fly or Mosquito
Size (Adult; Length): 8mm to 10mm (0.31" to 0.39")
Colorwheel Graphic Colors: yellow, black, brown, green, blue, purple
Descriptors: flying, biting, eye bands, green eyes, clusters,

Relative Size Comparison
Typical Size Between 8mm (0.3in) and 10mm (0.4in)
Lo: 8mm
Md: 9mm
Hi: 10mm
Territorial Map*
U.S., Canada, and Mexico
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Prince Edward Is.  
* MAP NOTES: The territorial heat map above showcases (in red) the states and territories of North America where the Yellow-Fly may be found (but is not limited to). This sort of data is useful when attempting to see concentrations of particular species across the continent as well as revealing possible migratory patterns over a species' given lifespan. Some insects are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America. States/Territories shown above are a general indicator of areas inhabited by the Yellow-Fly. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.


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