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Black Horse Fly

Common Name: Black Horse Fly.

Scientific Name: Tabanus Atratus.

What to look for?  Very large, black, sinister-looking fly! The Black Horse Fly is black, including wings. The color and size of the eyes stand out.  The huge eyes are silver. The eyes of the male Black Horse Fly meet in middle (holoptic). The eyes of the female are separated (dichoptic). They have prominent mouthparts, which are easily distinguishable and made of six piercing organs.

Where can they be found at Carillon Stonegate Pond? The Black Horse Fly will be active here from June to September. Look for them flying around the water’s edge and your flower garden. They will often perch on leaves of the plants surrounding our ponds and in our gardens. I found one visiting our Magnolia tree.

How big are they? Large! The Black Horse Fly averages approximately one inch in length; some reach two inches.

What are their flight patterns? They are fast fliers despite their brawny size.

How else do they behave? The Black Horse Fly (female) is a bloodsucking insect!

What’s for dinner? Blood, nectar and larvae – depending on their sex and point in life cycle! The female Black Horse Fly feeds on mammalian blood - especially cattle and other livestock. The male Black Horse Fly, which lack mandibles, feed on nectar and plant juices. Larvae feed voraciously on other insect larvae, other invertebrates and some small vertebrates.

Where do they take up residence? The Black Horse Fly resides in the eastern U.S. They have a very wide range of habitats, but will generally be near aquatic environments, which they need to lay eggs. They are most abundant near swamps and marshes, along pond and stream banks, and at the edge of wooded areas. And they also need to reside in proximity to populations of mammals for food supply.

When and where do they breed and nest? The Black Horse Fly generally breeds near aquatic environments. When the adult fly emerges, mating occurs. Eggs are laid on vegetation overhanging permanent water. Each female will lay several masses of hundreds to a thousand eggs each, in layers near water's edge. After laying eggs in a suitable environment for larvae to grow and develop, there is no further parental involvement. After the eggs hatch, the larvae will drop down into water or burrow into a moist environment. Larvae require two years to complete life-cycle, going through six to nine instars or molting stages before pupation.

Where do they migrate? The Black Horse Fly does not migrate.

Do they make any interesting sounds? No.

Interesting Facts About the Black Horse Fly:

  • The life cycle of the Blue Mud Wasp has four stages of development: egg, larva, pupa and adult.

  • Primary predator of the black widow spider – this is why you do not see black widow spiders while enjoying your outdoor patio!

  • While the Blue Mud Wasp has the ability to sting us, it is rarely aggressive so no need to be afraid.

  • Each spring, a new generation appears as an adult wasp chews a round hole in the end of the mud cell and exits its winter home.

For more information on the Black Horse Fly and sources of information used in this blog (these are the several of the sources that I am using to learn as I blog), please visit Iowa State University Bug Guide, University of Michigan Animal Diversity, University of Kentucky Entomology and University of Wisconsin

The Carillon at Stonegate community is very fortunate to have a variety of wetland, forest and prairie environments conducive to a variety of birds and other wildlife, insects and plants. Our community and the Kane County Forest Preserve do an exceptional job in maintaining this natural environment – both for the benefit of the birds and wildlife and for our residents to enjoy.


Take a hike and see what you can find – and identify!

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