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Robber Fly - Efferia (Efferia spp.)

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

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One could mistake a Robber Fly from the genus Efferia for some kind of strange black-and-white bee.

Updated: 07/29/2021; Authored By Staff Writer; Content ©www.InsectIdentification.org
Robber Flies are considered 'hanging thieves' because they use their arms to suspend themselves from twigs and branches. From this position, they monitor the skies around them, searching for unsuspecting flying insects. A passerby like a bee, wasp or other fly is not likely to see a Robber Fly as it roams between flowers or shrubs. If within range, with great speed, the Robber Fly chases the flying insect, and eventually overtakes it. Once caught, the Robber Fly uses its legs to hold the prey and carry it to a nearby plant. There, it uses its sharp mouth to stab the victim and suck out the insides.

All Robber Flies make a loud whirring noise as they fly because they beat their wings so rapidly. A male form the Efferia genus is slightly darker than the female. At the tip of the male's abdomen is black 'bulb' that looks like the rudder on a small airplane. Females do not have this feature; instead they have long needle-like ovipositors, which they use to inject their fertilized eggs into the soil. It may look like a stinger at first glance, but flies do not have stingers so people are safe from that threat. Both sexes can be found hanging around in open fields, parks, meadows, and other dry areas.

General Characteristics
Capability, Shape, Texture/Pattern, Benefits, Dangers
Fast insect icon
Flying insect icon
Shiny insect icon


Taxonomic Hierarchy
Species Breakdown
Kingdom: Animalia
  Phylum: Arthropoda
    Class: Insecta
      Order: Diptera
        Family: Asilidae
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          Genus: Efferia
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            Species: spp.
Identifying Information
Size, Colors, Features
Scientific Name: Efferia spp.
Other Name(s): Robberfly
Category: Fly or Mosquito
Size (Adult; Length): 13mm to 19mm (0.51" to 0.74")
Colorwheel Graphic Colors: white; black; gray; brown
Descriptors: flying, buzzing, noisy, fast, shiny, metallic

Relative Size Comparison
Typical Size Between 13mm (0.5in) and 19mm (0.7in)
Lo: 13mm
Md: 16mm
Hi: 19mm
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 Robber Fly - Efferia 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 Robber Fly - Efferia. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.


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