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

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.

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. 

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

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.

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.

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

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