Horse-fly (Chrysops relictus)

Close up of the head of a invertebrates_freshwater
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Horse-fly fact file

Horse-fly description


Apart from entomologists, there are probably few people who would actively look for horse-flies. For their size, they have one of the most painful bites of any insect and the bite can result in a painful swelling. The family Tabanidae is called deer-flies in the USA and horse-flies in Great Britain. They can cause problems in grazing animals by transmitting various diseases, including anthrax, and reducing milk output in dairy cattle. Blood-sucking is carried out only by the females and their mouth-parts have blade-like appendages that can cut through tough animal skin with ease. However, the flies themselves are not unattractive in appearance. Chrysops relictus is a stoutly-built insect, mostly shiny black but with variable yellow-orange bands around the upper part of the abdomen.

Body length: 10 mm
Wingspan: 22 mm

Horse-fly biology

Female horse-flies require blood to help produce eggs whereas males feed on nectar from flowers. Horse-flies lay their eggs in the mud of river banks or in damp earth. The larvae hatch and some are predatory, feeding on the grubs of other mud-dwelling insects. They can paralyse their prey by injecting them with venom, which also pre-digests the grub allowing the horse-fly larva to suck their victim dry. The larvae pupate just below the surface, and over-winter in this state. The adult flies emerge through small holes in the mud in May, and are on the wing until September.


Horse-fly range

Horse-flies have an extensive world range and are only absent from some isolated island groups such as Hawaii and the colder Arctic regions. They can turn up almost anywhere in Britain, especially in place where there is wet ground and grazing animals.

You can view distribution information for this species at the National Biodiversity Network Atlas.

Horse-fly habitat

This species can be found on wet heaths and moors and in woodland, particularly if there is mud or soft wet ground close by.


Horse-fly status



Horse-fly threats

There are believed to be no threats to the survival of this species.


Horse-fly conservation

There are currently no conservation projects for this species.

There may be further information about this species available via the National Biodiversity Network Atlas.

Find out more

For more on invertebrates and their conservation see Buglife, the invertebrate conservation trust:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:



Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
The process of forming a pupa, the stage in an insect’s development when huge changes occur that reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.



Image credit

Close up of the head of a horse-fly  
Close up of the head of a invertebrates_freshwater

© Robin Williams

Robin Williams
Kyntons Mead
Heath House
BS28 4UQ
United Kingdom


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