Insects and horses

Warm weather is on its way, and with it come the flies! Big or small, hairy or biting, blood-sucking or parasitic, these winged beasts are constant and troublesome companions for our equine friends. They are a source not only of annoyance and stress, but also disease and skin problems – both for our horses and for us! Animaderm has drawn up a profile for each of these flying insects, detailing the risks that they pose and giving advice on how to stay fully protected.

  Culicoides

• Appearance : Small midges (0.5 to 4 mm) that swarm in the late afternoon/at dusk and on cloudy, windless days 
• May be confused with : Simulium
• Species affected : Cows, horses, sheep, goats, sometimes people.
• Geographical spread : Worldwide
• Life cycle : Culicoides is a genus of midges that are active from April to October. They are most active around twilight or, in some cases, at night time (mostly notably C. pulicaris and C. imicola). Only females drink blood. Culicoides prefers shaded areas, which are sheltered from the wind and which are not too hot (15 to 35°C). It does not like low humidity, heat waves, or heavy rain. 
• Immediate effects : Annoyance/blood loss: physical and psychological fatigue, loss of appetite, weight loss, skin lesions, stress. Culicoides is the main cause of hypersensitivity to insect saliva, also known as summer dermatitis or sweet itch.
• Indirect effects : Transmission of viruses (such as equine infectious anaemia and West Nile virus, which occur regularly in southern France) and skin and eye parasites, including microfilaria that cause equine onchocerciasis. Symptoms include granulomatous and fibrous nodules, keratitis and uveitis. It affects mainly the face, neck, legs and abdomen.
• Targeted treatment and protection: Culicoides lives mainly in humid areas, where land and water meet, and in areas where vegetation is decomposing.Eggs are laid and larvae develop in aquatic or semi-aquatic environments: bodies of water, marshes, wet underbrush and meadows, ditches, dirty bedding, etc. They cannot fly far (only a few hundred metres), so adults remain close to where they were born.
• Do not keep manure, decomposing vegetation or stagnant water (whether storage tanks or drainage) near stables or grazing areas in order to limit the number of culicoides midges.  
• Keep troughs clean and change the water regularly. Clean out and disinfect stables and shelters very regularly, as culicoides can lay eggs in bedding and is particularly common in stables. 

  Simulium

• Appearance : Small, black, hump-backed flies (1 to 5 mm) that fly in swarms. 
• May be confused with : Culicoides
• Species affected : Mammals, including people
• Geographical spread : Worldwide
• Life cycle : Simulium is a genus of black flies which are active during the day and attack all mammals, in particular during warm and humid—and, above all, stormy—weather and primarily during the warmest hours of the day. They are most often seen flying in swarms close to the ground, moving in erratic motions. They also fly around the ears, nose, collar-line and abdomen. Only females drink blood. They bite rather than sting. They force their long mouth parts deep into the flesh and do not detach until they are full of blood. The bites are painful, and can lead to severe inflammation, itching and rashes, in particular around the ears. They can get inside clothes and under covers.
• Immediate effects : Annoyance/blood loss: physical and psychological fatigue, loss of appetite, weight loss, skin lesions, stress. Bites are often numerous, as the flies attack in swarms, and can cause serious inflammatory reactions, swelling, and patches of hyperkeratosis (thick, tough-looking skin), in particular inside the ears. Simulium flies are also a major cause of summer dermatitis, also known as sweet itch.
• Indirect effects : Transmission of viruses (such as equine infectious anaemia and West Nile virus, which occur regularly in Southern France) and skin and eye parasites, including microfilaria (Onchocerca gutturosa, O. reticulata, O. cervicalis) that can cause equine onchocerciasis. Symptoms include granulomatous and fibrous nodules, keratitis and uveitis. It affects mainly the face, neck, legs and abdomen.
• Targeted treatment and protection:
• Caps and masks are effective in protecting the ears against simulium attacks.
• Applying fat-based ointments around the ear reduces the risk of being bitten by simulium flies, as it prevents them from reaching the skin and attaching to hairs. Be careful when choosing which ointments you use: many of them may melt under the heat of the body (and under ambient heat, particularly when exposed to sunshine) and run into the ear canal.
• It is not advisable to cut the hair inside the ear. These hairs actually prevent dust and debris from gathering in the ear canal and stop insects and ticks from entering.

  Flies

  1 - LONG-NOSE FLIES 

a) HOUSEFLY (Musca domestica; common housefly)

• Appearance: Adult flies measure 6 to 8 mm long. They have longitudinal black bands on their thorax and a yellowish abdomen. They also have sucker-type mouth parts called a ‘proboscis’.
• Life cycle: Houseflies are attracted by animal faecal matter and by food and vegetation in various stages of decomposition. They are omnivorous and feed on organic matter (excrement, bodily secretions, decomposing animal and plant matter).
• Immediate effects: Even though they do not sting or bite, these flies are considered to be a pest as they annoy animals.
• Indirect effects: They can carry various pathogens (viruses, bacteria, parasites, etc.) which are transmitted to animals through saliva and faeces.
• Targeted treatment and protection: Baited traps and adhesive traps with or without bait are effective in reducing the number of flies.

b) AUTUMN HOUSEFLY (Musca automnalis; face fly)

• Appearance: Very similar to the common housefly, although a little bigger. Generally found on the head, in particular near the eyes and nose where it feeds on secretions.
• Species affected: Cows, horses.
• Geographical spread: Worldwide.
• Life cycle: Contrary to their name, autumn houseflies are active from spring to autumn, in particular on sunny days. They are most active around 25°C.
  Females lay eggs on fresh manure in fields. Larvae develop best in fresh cowpats; they grow much more rarely in horse manure, as it is too dry. Autumn houseflies are very capable flyers and can travel several kilometres in search of a host. They feed on all forms of bodily secretions: nose and eye secretions, sweat, blood and other biological liquids that seep from wounds or bites caused by other insects. They are hardly ever found in enclosed spaces during the active season.
• Immediate effects: same as M. domestica
• Indirect effects: same as M. domestica

   2 - STOMOXINE BITING FLIES

a) STABLE FLY (Stomoxys calcitrans; barn fly, biting housefly, dog fly, or power mower fly)

• Appearance: Similar to common housefly, from 5 to 10 mm in length. They are distinguished by their forward-facing biting mouth parts. Their bite is painful for both humans and animals.
• May be confused with: Common housefly, autumn housefly, horn flies.
• Species affected: Horses, cattle, also humans. Males and females feed on blood and bite animals mainly on their legs.
• Geographical spread: Worldwide.
• Life cycle: Stable flies are active between 15°C and 35°C, from spring to autumn, but may also be found in winter inside stables. They are active during the daytime, in particular around midday and in early afternoon in temperate regions. In tropical regions or warmer climates, they are generally most active both early in the morning and in late afternoon. Stable flies generally feed once per day but may feed more often depending on the temperature. They often feed in short, interrupted bursts as their bite is painful and they are forced to frequently change host during a single meal, which raises the risk of pathogen transmission.Although they can fly long distances to feed and to find more favourable conditions, stable flies remain close to their targets and travel little; they therefore spend almost all their time resting on walls, electric cables, posts and trees—even their hosts—with their heads facing upwards.
• Immediate effects: Annoyance/blood loss: physical and psychological fatigue, loss of appetite, weight loss, skin lesions, stress.
• Indirect effects: Disease transmission (equine infectious anaemia, leptospirosis, blackleg) and skin and intestinal parasites, including nematodes (Habronema microstoma) and helminths (Dermatobia hominis).
• Targeted treatment and protection: Stable flies lay eggs on decomposing organic matter (hay bales, straw and faecal matter, with a preference for horse manure), on which the larvae feed once hatched.
• Remove dung and used bedding regularly.
• Keep manure piles small and remove old hay and straw bales, even when stored away from stables and grazing areas, as stable flies are capable flyers.

b) HORN FLIES (Haematobia irritans; horn flies)

• Appearance: Similar to stable flies, but smaller (3.5 to 5 mm). Resemble common houseflies. Their bite is also painful. They generally bite with their head facing downwards.
• Species affected: Horses, cattle, also humans. They get their name from their habit of congregating around the base of cows’ horns. On horses, they generally congregate along the back, shoulders and abdomen.
• Geographical spread: Worldwide.
• Life cycle: Females lay eggs in fresh cow manure. Adults spend all their time on their hosts, leaving only for short flights and to lay eggs. Both sexes feed on blood day and night, feeding up to 20 times a day.Horn flies are present from May to October, peaking in activity in July and August.
• Immediate effects: Annoyance/blood loss: physical and psychological fatigue, loss of appetite, weight loss, skin lesions, stress.
• Indirect effects: Disease transmission (equine infectious anaemia, leptospirosis, blackleg) and skin and intestinal parasites, including nematodes (Habronema microstoma) and helminths (Dermatobia hominis).
• May be confused with: Common housefly, autumn housefly, stable flies.

  Horseflies (Tabanidae)

• Appearance: Large (0.6 to 3 cm depending on the species) with two wings, powerful flyers, stocky body. Often attack alone, irritating the target.
• Species affected: Horses, cattle, also humans.
• Geographical spread: Worldwide.
• Life cycle: Horseflies lay eggs in vegetation near to bodies of water (such as ponds or streams) or under plant litter in forests. Only the females feed on blood. In Europe, horseflies are active from mid-June to the end of August. Females feed during the daytime, often around midday, but some species are more active in early or late afternoon, or even early evening. Their bite is very painful; they pierce the skin using their mandibles and drink the blood that pours from the wound. What is more, females actively irritate their hosts so that they can find a good place to bite where they can feed until full without being chased away. If interrupted, they often immediately attack the same individual again, seeking to finish their feeding. Horseflies prefer areas close to woodlands, in which they like to rest.
• Immediate effects: Annoyance/blood loss: physical and psychological fatigue, loss of appetite, weight loss, skin lesions, stress. The wounds caused by horsefly bites can also attract other blood-sucking insects, which increases the risk of secondary infection and disease transmission.
• Indirect effects: Disease transmission (equine infectious anaemia, leptospirosis, blackleg) and skin and intestinal parasites, including nematodes (Habronema microstoma) and helminths (Dermatobia hominis).
• May be confused with: N/A
• Targeted treatment and protection: Horsefly traps.

  Hippobosca (Hippobosca equina; crab fly, forest fly, New Forest fly) 

• Appearance: Fly with a flat, hard body, of average size (5 to 8 mm), with head set into the thorax. Their robust feet have strong hooks with which they can hold on tight to hosts and move sideways in a crab-like motion. This has earned them the name ‘crab fly’.
• May be confused with: N/A
• Species affected: Mainly horses and cows. Sometimes attack people.
• Geographical spread: Worldwide.
• Life cycle: Hippobosca live almost exclusively on their hosts, preferably in areas where the skin is thin and protected, such as inside thighs, on the sheath and teats, and around the anus. They cannot fly far; they move across their hosts using their hooked feet or by flying in very short bursts. Both males and females feed on blood and their bite is painful. They are active from April to October, in particular during the summer.
• Immediate effects: Annoyance/blood loss: physical and psychological fatigue, loss of appetite, weight loss, skin lesions, stress. Horses may react violently to bites.
• Indirect effects: Disease transmission (equine infectious anaemia, leptospirosis, blackleg) and skin and intestinal parasites, including nematodes (Habronema microstoma) and helminths (Dermatobia hominis).

  Gasterophilus (Gastrophilus intestinalis, G. nasalis; horse botfly)

• Appearance: Large hairy fly, somewhat similar to a large bee, yellow to red-brown, powerful and noisy flyers. Their yellow eggs are laid in large, visible groups, often on animals’ legs. The larvae, found in fresh dung, resemble big red or white maggots (5 to 10 mm in diameter and 10 to 20 mm long) and are covered in rows of spines.
• Species affected: Horses.
• Geographical spread: Worldwide, almost exclusively where horses are present.
• Life cycle: The mouth parts of adult horse botflies are atrophied, meaning that they cannot feed. After mating, the females’ sole objective is to lay their eggs on their hosts’ hair. The larvae, on the other hand, are formidable parasites, which are specific to horses. Horse botflies are active from late spring to autumn. They can been seen during the day, in particular during the warmest hours, on horses living in fields or paddocks. Horses living in stables are considerably less at risk. Female horse botflies lay hundreds of yellowish eggs directly onto the horse’s hairs while in flight. Eggs are laid mainly on the horse’s legs, shoulders and head. The eggs can survive like that for several months. They hatch once scratched or licked. Stage-L1 larvae migrate into the mouth and nose and penetrate the mucous membrane, where they remain for a month before moving towards the stomach and intestines. They remain attached to the walls of the stomach using their mouth hooks for several months, where they grow through stages L2 and L3. They are then ejected in stools, where they grow into nymphs, then adults.
• Immediate effects: L1 larvae can cause ulcerations around the mouth, sometimes accompanied by hypersalivation. L2 and L3 larvae can also affect the digestive system, which can cause the host to become weakened and lose weight. They can also cause colic and even stomach or intestinal perforations, which can be fatal. As the L3 larvae are expelled, anal itching may be observed, which can lead to thinning of the tail.
• Targeted treatment and protection:
• Check your horse over regularly, particularly around the legs, head and shoulders. If you find yellow eggs stuck to the hair, remove them as soon as possible using a razor or tepid white vinegar to prevent the horse from ingesting the larvae.
• Worm the horse at the end of autumn using a treatment that is effective against botflies (such as Ivermectine).