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Horse Fly HORSE FLIES
& DEER FLIES
Critter Files/Insects/True Flies/Horse Flies and Deer Flies
By Blake Newton
University of Kentucky Department of Entomology
   
 
TAXONOMY

KINGDOM: Animalia | PHYLUM: Arthropoda | CLASS: Insecta | ORDER :Diptera | FAMILY: Tabanidae (horse flies and deer flies)

 
Other Names: Tabanids
 
WHAT ARE HORSE FLIES & DEER FLIES?
LIFE CYCLE
ECOLOGY
PEST STATUS
COMMON KENTUCKY HORSE FLIES
COLLECTING & PHOTOGRAPHY
HORSE FLY FACTS
MYTHS, LEGENDS, AND FOLKLORE
 
WHAT ARE HORSE FLIES & DEER FLIES?
Horse flies and deer flies are large flies known for their painful bites, and belong to the family Tabanidae.  Most horse flies and deer flies are at least as large as house flies, and generally have a similar shape as house flies.  Horse flies and deer flies can be distinguished from house flies and other flies by their unusual antennae (shown below): all horse flies and deer flies have 3 antennal segments, with the 3rd segment long and conspicuous.  Like all flies, horse flies and deer flies have only one pair of wings and have mouthparts adapted for sucking.
 
Horse fly Antennae
Horse fly Antennae (R. Bessin, 2004)
 

Common horse fly and deer fly species have brown, gray, or black bodies, and most have dark-colored or patterned wings.  Horsefly and deer fly larvae are legless and resemble large maggots.

SIZE: Adult body length up to 1 1/8", larvae up to 1 1/2"
 
LIFE CYCLE

Like all flies, horse flies and deer flies have complete metamorphosis with egg, larval, pupal, and adult stages.  The larvae are legless and maggot-like, and most species are found in water or moist soil.  After growing for 1-2 years (spending the winters as larvae) the larvae pupate in spring and emerge in early summer as winged adults.  The adults usually live for only a few days.  Females of most species lay eggs on aquatic plants that rise just above the water surface.

 
Horse Fly Larva
Aquatic Horse Fly Larva (B. Newton, 2005)
 
ECOLOGY

Adult horse flies and deer flies are commonly found near aquatic habitats where their larvae develop. Female horse and deer flies feed on the blood of large mammals, including livestock and humans.  Male horse and deer flies feed only on nectar.  Larval horse and deer flies are predators, and they usually live in ponds, streams, or moist soil.  They feed on a variety of aquatic invertebrates, including mayfly and dragonfly naiads, stonefly larvae, caddisfly larvae, crane fly larvae, snails, and aquatic worms.  Large horse fly larvae will sometimes capture and feed on small vertebrates, including fish and amphibians.  Larvae feed by sticking their head capsule completely inside prey and sucking fluids and internal organs. 

 
PEST STATUS

Female horse flies and deer flies can be a serious nuisance, giving painful bites to humans, pets, and livestock.  Some people have serious allergic reactions to the bites, and deer flies will sometimes transmit tularemia (a bacterial disease) to rabbits, livestock, pets, and humans.  Read more about pest horse flies and deer flies in our online factsheet: Horse Flies & Deer Flies

 
COMMON HORSE FLIES & DEER FLIES

HORSE FLIES
GENUS: Tabanus, others
Most of horse flies found in Kentucky belong to the genus Tabanus. Adults are typically 1/2" or larger, up to nearly 1 1/4". Most species are mottled-gray or black.

 
Black Horse Fly
Black Horse Fly (R. Bessin, 2004)
Horse Fly
Horse Fly (R. Bessin, 2004)
DEER FLIES
GENUS: Chrysops
Deer flies are typically smaller (1/4" - 1/2") than horse flies and usually have patterned wings.
 
Deer Fly
Deer fly (R. Bessin, 2000)
 
COLLECTING & PHOTOGRAPHY

Horse flies and deer flies are commonly found near ponds and streams during the summer in Kentucky, especially around farms where livestock is kept.  Horse flies and deer flies are strong fliers, so a butterfly net (also called an "aerial net") may be needed to capture one.  Larval horse flies and deer flies are common in ponds and streams, and can be collected with aquatic insect nets.  Photographing horse flies and deer flies can be difficult, but they will sometimes stop and rest on flowers and leaves, and will remain still if you approach slowly with a camera.

 
HORSE & DEER FLY FACTS

Although most flies have mouthparts adapted for sucking, female horseflies are able to cut into flesh with their knife-like mouthparts.

Like all aquatic insects, horse fly and deer fly larvae require clean water to live.  Because of this, scientists can tell if a stream is polluted or not based on what types of aquatic insects are present.  Read more about using insects to determine water quality:
http://www.aces.edu/pubs/docs/A/ANR-1167/ANR-1167.pdf

 
MYTHS - LEGENDS - FOLKLORE

Do you know any myths, legends, or folklore about horse flies or deer flies?  If you do, let us know!


Original document: 20 April 2005
Last updated: 20 April 2005

Photos courtesy R. Bessin and B. Newton, University of Kentucky
The Kentucky Critter Files are maintained by Blake Newton, Department of Entomology, University of Kentucky.
Contact: blaken@uky.edu

 

University of Kentucky Entomology/Kentucky Critter Files/Kentucky Insects/True Flies/Horse Flies & Deer Flies