Tabanus atratus

Ge­o­graphic Range

Ta­banus atra­tus is pri­mar­ily found in the east­ern United States, al­though it has been col­lected through­out the en­tire con­ti­nen­tal US. (Roberts and Janovy Jr., 2000)

Habi­tat

This horse­fly is able to sur­vive in a wide range of habi­tats al­though it can­not sur­vive in ex­treme cli­mates such as moun­tain tops or deserts. It re­quires moist en­vi­ron­ments in which to lay eggs, and mam­mals to feed on. ("Wel­come to the World of the Horse­flies", 2000)

Phys­i­cal De­scrip­tion

Adults of this species reach 20-25 mm in length. The flies can be en­tirely black, in­clud­ing the wings, or dark brown to black­ish pur­ple. Ta­banus atra­tus have large com­pound eyes, which are di­chop­tic (sep­a­rated) in fe­males, and holop­tic (con­tin­u­ous) in males. They have promi­nent mouth­parts, which are eas­ily dis­tin­guish­able: The fas­ci­cle is made of six pierc­ing or­gans. Start­ing from the out­side, there are 2 flat­tened, blade­like mandibles with tooth like ser­ra­tions used for cut­ting. Two nar­row max­il­lae also ser­rated used to pierce the tis­sue and blood ves­sels of the host, a me­dian hy­pophar­ynx and a me­dian labrum-epiphar­ynx. The hy­pophar­ynx and labrum-epiphar­ynx make up the food canal, while the labrum is a large sponge like organ used to lap up blood (Roberts and Janovy, 2000). Short stout hairs cover the body, and wing ve­na­tion is pro­nounced.

Larva of Ta­banus atra­tus are sim­i­lar to the lar­vae of all other horse­flies. Lar­vae can be white to tan, while pos­sess­ing a slen­der, cylin­dri­cal body, which ta­pers at the head. (Strother, 2000) Like other ta­ban­ids, the larva of the black horse­fly has twelve seg­ments and a re­tractable tra­cheal siphon used for res­pi­ra­tion. The re­tractable head of the larva has two sharp mandibles that can cause a painful bite (Roberts and Janovy, 2000). The pupae have a se­ries of spines stick­ing out from the ab­dom­i­nal seg­ments, and usu­ally ex­hibit lit­tle move­ment (Hutchin­son, 1999). (Hays, 1956; Hutchin­son, 1999; Roberts and Janovy Jr., 2000; Strother, 2000)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range length
    20 to 25 mm
    0.79 to 0.98 in

De­vel­op­ment

Horse flies pass through the fol­low­ing holometabolous life stages: egg, larva, pupa, and adult. After the eggs hatch, the lar­vae will drop down into water or bur­row into a moist en­vi­ron­ment where it then ma­tures through six to nine in­stars be­fore pu­pa­tion (Hutchin­son, 1999). In colder cli­mates, lar­vae will over­win­ter, then move to drier soil to in order to pu­pate (Strother, 2000). The pupal stage lasts from one to three weeks. (Hays, 1956; Hutchin­son, 1999; Strother, 2000)

Re­pro­duc­tion

Ta­banus atra­tus gen­er­ally breed near aquatic en­vi­ron­ments. When the adult fly emerges, mat­ing oc­curs. Fe­males then search for a blood meal, while males feed on nec­tar. (Hutchin­son, 1999; Strother, 2000)

Each fe­male will lay three to four masses of one hun­dred to a thou­sand eggs each, in lay­ers near water's edge or some­where quite close to water. ("Wel­come to the World of the Horse­flies", 2000; Hutchin­son, 1999)

  • Range eggs per season
    300 to 4000

After search­ing for and lay­ing eggs in a suit­able en­vi­ron­ment for lar­vae to grow and de­velop, there is no fur­ther parental in­volve­ment.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female

Be­hav­ior

Horse­flies are ac­tive dur­ing the day­time, and once a host is found, the horse­fly will at­tack re­lent­lessly in order to feed (Strother, 2000). Adult flies can fly over 65 kilo­me­ters, but will gen­er­ally not dis­perse more than 2 miles away from where they emerged. The flies rest on paths and roads, es­pe­cially in wooded areas. When­ever the wind picks up or tem­per­a­ture drops, a sig­nif­i­cant de­crease in flies can be ob­served. Ta­banus atra­tus is also at­tracted to light, com­monly con­gre­gat­ing at light sources dur­ing the night (Green­val­ley, 2000). ("Wel­come to the World of the Horse­flies", 2000; Strother, 2000)

Food Habits

The fe­males of T. atra­tus feed on mam­malian blood, while males, which lack mandibles, feed on nec­tar and plant juices (Hutchin­son, 1999). A blood meal is nec­es­sary in order for fe­males to nour­ish their de­vel­op­ing eggs (Strother, 2000). Horse­flies are di­ur­nal, usu­ally feed dur­ing the day (Green­val­ley, 2000). The mouth­parts are made of six pierc­ing or­gans: two mandibles; two max­il­lae; hy­pophar­ynx; and a labrum-epiphar­ynx. The mandibles and the max­il­lae have sharp ser­rated teeth on them, which are used for punc­tur­ing the skin and rup­tur­ing blood ves­sels (Roberts and Janovy, 2000). The labrum then func­tions to lap up the pool of blood that is formed from the bite, oth­er­wise known as tel­mophagy (Hutchin­son, 1999). When search­ing for a host, fe­males are at­tracted to large, dark, mov­ing ob­jects and to CO2. Lar­vae feed vo­ra­ciously on other in­sect lar­vae, other in­ver­te­brates and small ver­te­brates (Strother, 2000). ("Wel­come to the World of the Horse­flies", 2000; Hutchin­son, 1999; Roberts and Janovy Jr., 2000; Strother, 2000)

  • Animal Foods
  • blood

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

This species pro­vides no major eco­nomic ben­e­fit to hu­mans.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Al­though Ta­banus atra­tus do not often bite hu­mans, when it does hap­pen it leaves painful mem­o­ries. This fly can also trans­mit bac­te­r­ial, viral, and other dis­eases such as surra and an­thrax, to both hu­mans and other an­i­mals through its bite.

The ef­fect of T. atra­tus on live­stock can be a se­ri­ous prob­lem. Blood loss and ir­ri­ta­tion from the flies can se­verely af­fect beef and milk pro­duc­tion, as well as graz­ing. Live­stock usu­ally have no way of avoid­ing the painful bites, and mil­lions of dol­lars have been spent try­ing to con­trol these pests. (Roberts and Janovy Jr., 2000; Strother, 2000)

Con­ser­va­tion Sta­tus

This species re­quires no spe­cial con­ser­va­tion sta­tus.

Con­trib­u­tors

Sara Di­a­mond (ed­i­tor), An­i­mal Di­ver­sity Web.

Wil­son Long (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Barry OCon­nor (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sanguivore

an animal that mainly eats blood

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

Ref­er­ences

2000. "Wel­come to the World of the Horse­flies" (On-line). Ac­cessed March 2, 2001 at http://​www.​greenvalleypc.​com/​frontpage.​htm.

Hays, K. 1956. A Syn­op­sis of the Ta­ban­idae (Diptera) of Michi­gan. Ann Arbor: Uni­ver­sity of Michi­gan. Mu­seum of Zo­ol­ogy.

Hutchin­son, R. 1999. "Horse Flies" (On-line). Ac­cessed March 3, 2001 at http://​www.​roberth.​u-net.​com/​.

Roberts, L., J. Janovy Jr.. 2000. Foun­da­tions of Par­a­sitol­ogy. Boston: The Mc­Graw-Hill Com­pa­nies, Inc..

Strother, S. 2000. Ta­ban­ids (horse­flies). Der­ma­tol­ogy On­line Jour­nal, 5(2): 6.