A recent tragic story in Horse & Hound’s news pages highlighted the potential for disaster when horseflies strike.
When ex-racehorse Black Attack, nicknamed Sooty, was targeted by three horseflies biting his chest, he reared up and fell over backwards. The injuries he sustained as he crashed down onto concrete meant that he had to be put to sleep.
Sooty’s owner Catherine Jones says that the rearing was entirely out of character.
“It was as if he was getting a shock,” says Catherine, explaining that the eight-year-old gelding had just been sprayed with flyspray before the attack. “When he hit his head [on the concrete] he starting fitting. We called the vet immediately, who came out within 10 minutes and put him down. It’s extremely upsetting.”
Although Sooty’s reaction was extreme, it is not unheard of for horses to panic when targeted by horseflies. Owners and riders on the H&H forum report their animals lashing out or fleeing from horsefly attacks.
“[He was] rearing, kicking out and galloping around the field,” said one owner after witnessing her horse being driven to distraction by these persistent flying pests.
What makes horsefly bites so painful — and how concerned should we be about the welfare
of our horses during the summer months?
Knowing the enemy
“Flies plague horses at this time of year, with horseflies being the worst,” admits vet Karen Coumbe MRCVS. “Essentially, there are two different kinds of flies that bother horses: biting and nuisance flies.
“Horseflies are the biggest biting flies. They have vicious mouthparts that enable them to pierce the horse’s skin and feed on his blood.
“The nuisance flies have gentler mouthparts designed to lap fluids found in and around the horse’s eyes, mouth and nose — or worse, around wounds.
“Both types spread infections and can cause nasty skin sores.
“An individual horsefly bite produces a markedly painful, itchy skin reaction with a central bite mark, often with a blood spot. Each individual bite is sore, with itchy after-effects and a swelling reaction that lingers.
“Even if you or your horses are not bitten often, you will remember each occasion all
“With age, most horses become more wary and/or wise about the horseflies they encounter. Some horses, however, can become very agitated.
“This is not helped by the fact horseflies can be very persistent and are not always deterred by attempts at swatting them away. They will generally persist in attacking until they strike their target and some flies almost seem to give chase.
“This will worry horses, who will fidget at best and attempt to flee at worst — which is when accidents happen.”
“Most biting flies are attracted to movement, dark colours and the heat from a large animal such as a horse,” adds Karen.
“Horseflies prefer daylight and rarely enter barns or shady areas, so grazing animals at night and providing shelter during the day can help to provide some relief from these large flies.
“Some research has shown that in the world of the horsefly a grey horse is not nearly as attractive as a brown or black horse. It may not be a coincidence that most fly rugs are produced in light colours.
“There is no one perfect control measure — if there was, we would all be using it. However, since horseflies lay their eggs on vegetation close to water, control measures include eliminating potential breeding grounds as well as using fly repellents.
“Unfortunately, any fly repellent that is truly effective in actually killing flies is too toxic to use on horses.
“Horse skin is surprisingly delicate and it is wise to test any new repellent on a small area before you spray it all over.
“Fly fringes, masks and rugs — ideally impregnated with insecticide — are beneficial, but will never prevent all the fly bites.
“We are fortunate in the UK that there are few serious fly-borne illnesses. In some countries, insects can cause major suffering by spreading potentially fatal diseases from horse to horse, such as Equine Infectious Anaemia (EIA), a virus that is transmitted by large blood-feeding insects such as horseflies.
“Favourite biting sites are the underbelly, legs, neck and withers, which are not easily covered by a flysheet. Therefore stabling is beneficial when the flies are really bad on hot, sultry days. They are best avoided, if possible, as 20 to 30 flies can take 100ml of blood in a six-hour period of feeding, and the blood trickles they leave will attract more flies.
“It is questionable whether horseflies really are increasingly prevalent, or whether it is just that they are so unpleasant that we tend to notice them particularly.”
According to National Trust entomologist Matthew Oates, there are definitely more horseflies around this summer than would normally be the case.
“All told, there are around 30 species of horsefly that live in the UK,” says Matthew. “They come in various shapes and sizes, some of them giant. Most species are quite rare, however, and live in specific places such as the New Forest.
“The most common types of horsefly are the common cleg (haematopota pluvialis) and the common brown (tabanus bromius). Both are particularly numerous this year.”
Recent weather patterns are chiefly responsible for their proliferation, explains Matthew.
“These species breed in the mud and very wet conditions, so they most certainly benefited from the mild, wet winter and the very high water table,” he says. “Although it has been dry, there are still puddles around and mud is still wet.
They breed in damp woodland areas and love flying in warm weather, so June and July have provided perfect conditions.
“The hotter it is, the hungrier they become,” he adds. “It’s the female horseflies that bite, not the males, as they need a ‘blood meal’ to help develop their eggs.
“The lifespan of a horsefly varies between species, but the common cleg generally lasts around two to three weeks.
“While the season for the common cleg should finish in early August, other species — including some of the bigger horseflies — will still be around in September.”
As Karen explains, there is no complete barrier to horseflies, but there is much owners can do to at least limit the chances of them driving horses to distraction before the pests leave us at the end of next month.
This article was first published in Horse & Hound magazine (14 August 2014)