Importance
- There are over 150,000 species of flies worldwide. Many species are beneficial as they pollinate plants and break down organic matter. However, several flies can transmit pathogens to people and animals.
- Flies can negatively impact animals by causing irritation, stress, reduced production (lower weight gain and milk production), and disease. Flies can transmit pathogens through biting and blood feeding (biological vector) or by carrying pathogens on their bodies (mechanical vector). Signs of illness associated with flies may include fever, lethargy, skin sores, hair loss, and anemia.
- Foreign vectors and foreign animal diseases (FADs) are not found in the United States and can threaten human and animal health. FADs can be introduced to the United States, so animal owners and veterinary personnel have a key role in recognizing and reporting FADs to animal and public health officials. Early signs of fly-related FADs may include:
- Unusual appearance or activity of flies or larvae (maggots)
- Large number of sick or dead animals
- Unusual signs of illness (like painful and enlarging wounds that smell of decay)
About Flies
- The fly life cycle includes the egg, larva (maggot), pupa, and adult. In warm weather, some flies can complete all stages within one to two weeks.
- Immature flies need moisture to develop. Adult females lay their eggs in water or wet organic matter, such as manure or decaying material like dead animals.
- Biting flies have either scissor-like or piercing-sucking mouthparts used to feed on the blood of animals and sometimes people. Blood meals are needed for female biting flies to develop their eggs.
- Non-biting flies have specialized mouthparts designed for sponging up liquids.
- Screwworm flies require living animal tissue for development. Eggs are laid in or near wounds or mucous membranes. Larvae feed on the living tissue of their host, causing large, painful wounds that enlarge over time and attract more flies to lay eggs until the host is either treated or dies.
Identification of Flies
- Many fly species can be identified by appearance, behavior, and habitat. Some flies, especially immature stages, may be difficult or impossible to identify without the help of a dissecting microscope or trained entomologist.
- Adult flies vary in color, shape, and size from tiny (1-3mm) to large (15-20mm).
- All flies have six legs and one pair of functional wings. The hind wings are small, vestigial structures called halteres.
- Mouthparts may be short or long and used for sucking, piercing, or biting.
- Antennae may be short or long with varying segments.
- Fly larvae (maggots) are usually worm-like, with no distinct head or legs. Size, color, and shape may be used to identify species.
- Identification keys and fly experts can be consulted for further details.
Endemic Flies of Animal Health Concern
The flies listed below (arranged by size from largest to smallest) are commonly found in the United States. In certain areas, these flies may transmit pathogens. Endemic diseases in animals may or may not be reportable, depending on the jurisdiction.
Shutterstock
Name: Tabanus, Haematopota spp. (Horse Fly)
Characteristics: Large (6-20 mm) biting fly; stout bodies, large metallic or iridescent eyes; only females blood feed.
Habitat: Streams, marshes, and wooded areas throughout most of the U.S., except Hawaii.
Endemic Diseases:
Anaplasmosis (A. marginale)
Anthrax
Equine infectious anemia
Tularemia
Jesse Rorabaugh, inaturalist, public domain
Name: Lucilia, Phormia, Cochliomyia spp. (Blow Fly)
Characteristics: Medium (8-16 mm) non-biting fly; robust, shiny metallic blue, green, or black bodies and large, reddish eyes.
Habitat: Found in urban, rural, and forested areas; eggs laid on dead animals, open wounds, or decaying organic matter; widely distributed in the U.S.
Endemic Diseases:
Myiasis (larva grow inside host and feed on tissue, resulting in tissue damage and secondary infections)
Anthrax
Colibacillosis (E. coli)
Salmonellosis
Campylobacteriosis
Johan Pretorius, inaturalist, CC BY-NC-4.0
Name: Oestrus ovis, Gasterophilus spp. (Bot/Warble/Heel/Gad Fly)
Characteristics: Medium (6-20mm) non-biting fly; chunky, bee-like appearance with hairy bodies and rounded heads; larvae feed on tissues of host.
Habitat: Eggs laid on or near a host; thrive in tropical and subtropical climates, but also found in temperate regions; throughout the U.S.
Endemic Diseases:
Myiasis (larva grow inside host and feed on tissue, resulting in tissue damage and secondary infections)
Shutterstock
Name: Chrysops spp. (Deer Fly)
Characteristics: Medium (6-13 mm) biting fly; large, brightly colored eyes which can be iridescent, wings are clear with dark bands or patterns, only females blood feed.
Habitat: Wooded, wetland and damp areas, eggs laid on vegetation near water, larvae require aquatic to semi-aquatic habitat; broad geographic distribution.
Endemic Diseases:
Tularemia
Equine infectious anemia
Anaplasmosis (A. marginale)
Jerry Lanfear, inaturalis, CC by 4.0
Name: Musca autumnalis (Face Fly)
Characteristics: Medium (6-8 mm) non-biting fly; similar in appearance to house flies, grayish-black color with four dark stripes on body.
Habitat: Prefer pastured cattle and horses, feeding on secretions from eyes, nose, and mouth; eggs laid in fresh cow manure; found throughout the U.S., particularly temperate regions.
Endemic Diseases:
Dermatophilosis
Pinkeye in cattle (Moraxella)
Eye worm (Thelazia lacrymalis)
txwoofus, inaturalist, CC-BY-NC-SA-4.0
Name: Stomoxys calcitrans (Stable Fly)
Characteristics: Medium (6-8 mm) biting fly; resemble house flies but lighter color and spotted abdomen, both males and females blood feed.
Habitat: In and around livestock areas; breed in decaying organic matter or decaying vegetation; broad geographic distribution.
Endemic Diseases:
Anthrax
Colibacillosis (E. coli)
Contagious mastitis
Dermatophilosis
Salmonellosis
Ulcerative lymphangitis
Shutterstock
Name: Melophagus ovinus (Sheep Ked)
Characteristics: Medium (7mm) biting fly; reddish brown, wingless, covered in short, bristly hairs, eggs hatch internally so female lays mature larvae that are glued to animal’s fleece, numbers are highest in winter.
Habitat: Lives less than one week off host (sheep); widely distributed.
Endemic Diseases:
Anemia
Damaged wool and hide (cockles)
Shutterstock
Name: Musca domestica (House Fly)
Characteristics: Medium (6-7 mm) non-biting fly; grayish black in color with four stripes on thorax (upper body).
Habitat: Commonly found in confined animal production as well as urban habitats, primarily areas with human or animal waste and food waste; eggs laid in moist, decaying organic matter; widely distributed
Endemic Diseases:
Campylobacteriosis
Colibacillosis (E. coli)
Cryptosporidiosis
Pinkeye in cattle (Moraxella)
Porcine reproductive and respiratory syndrome (PRRS)
Salmonellosis
Streptococcosis
Swine dysentery
Transmissible gastroenteritis
Turkey coronavirus
Many others
Judy Gallagher, inaturalist, CC BY-SA 4.0
Name: Haematobia irritans (Horn Fly)
Characteristics: Small (3.5-5 mm); brownish-gray or black bodies. They have two parallel stripes on their bodies; both males and females blood feed and remain on their animal hosts between feedings.
Habitat: Primarily blood feed on cattle and often cluster on back, sides, or belly; eggs are laid in fresh cow manure; found throughout the U.S.
Endemic Diseases:
Ulcerative lymphangitis
Dermatophilosis
Granulomatous dermatitis (due to nematode Stephanofilaria stilesi)
Xpda, inaturalist, CC BY-SA 4.0
Name: Simulium spp. (Black Fly/Buffalo Gnat)
Characteristics: Small (1-5 mm) biting fly; shiny black to various shades of gray or yellow with a humpbacked appearance; only females blood feed and remain.
Habitat: Prefer running rivers and streams; eggs are laid on vegetation just below the water surface; widely distributed in the U.S.
Endemic Diseases:
Vesicular stomatitis
Leucocytozoonosis
Severe anemia, toxic shock, exsanguination (associated with mass attack)
James Gathany, CDC Public Health Image Library, public domain
Name: Lutzomyia spp. (Sand Fly)
Characteristics: Small (1.5-3.5 mm) biting fly; hairy bodies and wings, wings are held in a distinctive V-shape at rest and tips of wings are pointed not rounded as in other flies; nocturnal; only females blood feed.
Habitat: Prefer damp, dark places, such as cracks in walls, animal burrows and leaf litter; found in warm areas in southern U.S.
Endemic Diseases:
Leishmaniasis (biological vector)
Vesicular stomatitis
Shutterstock
Name: Culicoides spp. (Biting Midge/No-See-Um)
Characteristics: Tiny (1-3mm) biting fly; grayish in color (reddish when filled with blood); most active at dusk and dawn; only females blood feed.
Habitat: Moist environments (swamps, marshes, edges ponds and lakes, piled animal manure, moist leaf litter); more than 150 species throughout the U.S.
Endemic Diseases:
Bluetongue
Epizootic hemorrhagic disease
Vesicular stomatitis
Burning, itching, red welts from bites
Foreign Flies of Animal Health Concern
The flies listed below are selected vectors of highly contagious, reportable, or foreign diseases of animals. Learn more about recognizing and reporting foreign ticks and FADs at CFSPH: FAD Prevention.
Name: Cochliomyia hominivorax (New World Screwworm)
Characteristics: Large (8-10 mm) non-biting fly, about the size of a house fly or slightly larger; distinctive metallic blue or green coloration, three dark stripes along its back, and large orange eyes.
Larvae are creamy white, cylindrical with encircling bands of spines and taper at both ends; larvae eat tissues of living animals (non-necrotic tissue).
Habitat: Tropical and subtropical regions of Western Hemisphere; recent cases in Caribbean, Central America, and Mexico; eggs are laid near open wounds, navel, or mucous membranes of living animals or people.
Foreign Diseases:
New World screwworm myiasis (larvae eat tissues of living animals)
Name: Chrysomya bezziana (Old World Screwworm)
Characteristics: Large (8-12 mm) non-biting fly; metallic green or blue with a yellow face.
Larvae are creamy white but lack obvious body processes, except the last segment; larvae eat tissues of living animals (non-necrotic tissue).
Habitat: Tropical and subtropical regions of Asia, Africa, the Middle East, India and Papua New Guinea; eggs are often laid near open wounds, navel, or mucous membranes of living animals or people.
Foreign Diseases:
Old World screwworm myiasis (larvae eat tissues of living animals)
Alan R. Walker, Wikipedia, CC BY-SA 3.0
Name: Glossina spp. (Tsetse Fly)
Characteristics: Large (6-16mm) biting fly; brown with long proboscis (mouthpart) and folded wings that lay on top of each other when at rest. Both males and females blood feed.
Habitat: Sub-Saharan Africa; typically inhabit woodlands but can be found in open grasslands.
Foreign Diseases:
Trypanosomiasis
ajott, iNaturalist, CC BY 4.0
Name: Hippobosca longipennis (Dog Louse Fly)
Characteristics: Medium (5-7 mm) biting fly; flattened, reddish-brown body and yellowish underside; wings often held flat over the body; males and females blood feed.
Habitat: Africa, Middle East, Asia, southern Europe; distribution is limited by low temperatures and high humidity; primarily infest dogs but can be found on other animals; females give birth to larvae rather than laying eggs.
Foreign Diseases:
Canine filarial parasite (Dipetalonema dracunculoides)
Significant irritation and extensive blood loss possible
Marie Lou Legrand, iNaturalist, CC BY-NC 4.0
Name: Musca vitripennis (Muscoid Fly)
Characteristics: Medium (6-7mm) non-biting fly similar in appearance to the house fly (gray body with dark stripes).
Habitat: Europe, Asia, Africa; decaying organic matter.
Foreign Diseases:
Intermediate host for Parafilaria bovicola
Significant irritation
Collection and Submission of Flies
- Flies of concern should be collected for identification to ensure effective control measures are used.
- Testing may be available to determine if pathogens are present or insecticide resistance is developing.
- Adult flies can be collected with insect nets or fly traps. Different types of attractants and traps may be needed depending on the species.
- Care should be taken not to crush or damage the insect.
- Fly eggs, larvae, and pupae can be collected from the animal or the environment.
- If collecting larvae from a wound, get a representative sample by using forceps to gently remove larvae from several sites and depths.
- Adult flies can be collected with insect nets or fly traps. Different types of attractants and traps may be needed depending on the species.
- Laboratories and shipping companies may have specific instructions for you to follow.
- Place adult flies in a labeled, sealed, hard-sided container and keep dry and cool in a refrigerator or freezer.
- Place larvae and pupae in a labeled, sealed, leak-proof container submerged in 70-90% ethanol. Rubbing alcohol, hand sanitizer, or clear cocktail alcohol (80 proof or higher) will also work, if needed. Place the container inside a sealable bag (e.g., Ziploc®).
For additional tips, visit How to Submit Vectors for Identification.
Control and Prevention of Flies
- Fly populations can be managed by disrupting their life cycle and habitat.
- For prompt detection and control, continuously monitor flies in animal housing areas. Appropriate monitoring methods differ by species; consult a veterinary entomologist for best methods for species of concern in your region.
- Frequently inspect animals for fly larvae (maggots).
- Reduce moisture in and around animal areas (such as breaking up manure and other organic debris weekly or spreading it into thin layers to dry) to reduce immature fly development. Composting animal and feed waste can limit suitable habitat for fly development.
- Consider ways to encourage natural predators like birds, bats, and invertebrates to help reduce fly populations.
- Keep flies away from animals and animal housing areas.
- Keep animals indoors during high fly activity, use fans to create air movement, install screens on windows, and set up fly traps near animal areas.
- A variety of fly repellents and insecticides are available for animals, including topical pour-ons, sprays, and ear tags. Be sure to choose a product with an EPA registration number (topicals) or an FDA (A)NADA number (orals and injectables). Read the product label carefully to make sure it is effective against flies and safe for the species and age of animals to be treated.
- Promptly treat animals with any wounds, diseases, or secondary infections.
- Isolation of the animal and supportive care may be needed.
- Fly control products should only be used after consulting with experts to prevent unintended harm to wild animals and invertebrates, like frogs and honey bees. These products can also contaminate water sources.
- Avoid moving flies from one site to another.
- Check animals closely for fly larvae (maggots) in wounds before movement.
- Quarantine, inspect, and monitor new and returning animals in a separate area.
- Some pathogens that are spread by flies can be prevented through the use of vaccines, such as Moraxella bovis (pinkeye in cattle).
For additional guidance, visit Considerations When Managing Vectors.
Learn More
Additional information on flies, their impacts on animals, and control can be found below.
Endemic flies
Foreign flies
Note: This webpage shows some of the most significant vectors of concern to domestic animals in the United States. It is not meant to be a complete resource of all arthropods, their associated diseases and conditions, or used as a diagnostic tool. Veterinary consultation is advised for clinical cases.