A midge charm

Breeze God

Get up and scatter the armies of the itchy witch

Rain God

Ruin their gathering veil

Cloud God

Forbid this travesty of your image

Horse God

Shake your heathery mane

Water God

Splash your frown of ripples

Hill God

Lead us out of all hollows

Turf God

Preserve us with your smoke

Frost God

Put on your white coat

And lock them all away!

By Sean Lysaght

IF you have ever had the great good fortune to visit the beautiful Ballycroy National Park in Co. Mayo, you’ll have encountered this poem prominently displayed on the wall outside the café in the visitor’s centre.

Summer expeditions in Ireland’s scenic outdoors will probably also have acquainted you with one of our least hospitable species: the midge! Midges, or Culicoides to give them their official title, are small, weak-flying biting insects that breed in still water.

As the poem explains, they can’t travel over long distances or fly well in the wind, so they tend to feed at night and are most active near ponds, lakes, and dense stands of trees or undergrowth when the air is warm and calm.

If you wander in to a cloud of midges you’ll quickly find yourself beating a hasty retreat, due to their irritating bites. For most people and animals, they’re just an unpleasant nuisance. However, some unfortunate horses are allergic to the midges’ saliva and they develop an intense itch once bitten. This condition is known as “sweet itch” and it’s the most common skin allergy suffered by horses.

There are hundreds of different Culicoides species and they vary in their preferred feeding sites. Those found in this part of the world tend to bite horses along their mane, withers, topline and hindquarters/tail. Most affected horses suffer two different types of allergic reactions: the first results in small, hive-like bumps which appear almost immediately after being bitten. This is followed by a more generalized response 24-48 hours later. Both these immune responses result in such severe itchiness that the horse will rub the affected skin areas incessantly, breaking the hairs and eventually resulting in characteristic greyish, thickened skin ridges and bald or raw patches.

The midges breed from April to September in Ireland, so affected horses are usually fine over the winter months but the problem reoccurs every summer. In addition to the skin damage and altered appearance, sweet itch is a serious welfare problem for the unfortunate animal, as they are tormented by the itch. Secondary skin infections are common and your vet may have to prescribe a variety of medications to try to control the irritation and encourage the skin to heal.

Unfortunately, once a horse or pony develops sweet itch, there is currently no effective cure. It becomes a case of managing the animal and their environment to minimise their exposure to midges. You will have to take steps every summer to try and prevent the horse getting bitten, as once they start to scratch it rapidly becomes a vicious circle of incessant skin damage. It’s important to be proactive and put effective midge control measures in place each spring, before the horse has the chance to become bald, itchy and miserable.

Medication and treatments

A variety of medications have been tried to control sweet itch, but all have their drawbacks. Antihistamines can reduce the severity of the initial hive-like response to the midge saliva but these drugs need to be given several times a day, which is just not practical for most horse owners.

Corticosteroids are medicines that dampen down the immune response. They are available in long-acting formulations that can stop the horse reacting to the midge bites and becoming itchy. This sounds great but the potential problem with this approach is the risk of laminitis. Severe foot inflammation is a potential side effect of long-acting corticosteroids in horses. Corticosteroid-induced laminitis could be severe enough to warrant the horse being put down on welfare grounds, so the risk is typically not worth taking in a case of sweet itch, as there are safer ways to manage the problem.

Fly repellants can be sprayed on to the horse’s coat to discourage midges from approaching. They need to reapplied frequently, especially if the horse is sweating, and their efficacy is dubious, with many midges seeming undeterred by their presence.

Insecticides are chemicals that kill insects. Pyrethrins and permethrins fall into this category and are available as shampoos or pour-on treatments for horses. Some products need to be diluted before use and can be irritating to human tissues, so follow the label instructions carefully during application and disposal. Insecticides need to be reapplied throughout the fly season and if the occasional midge manages to bite the horse before being affected, the horse will still get itchy.

Fly sheets

Full body fly sheets have become available in recent decades and they offer a safe and often very effective way to protect the horse from insect bites.

The sheets are typically composed of a fine, stretchy mesh. They are carefully designed to cover the entire body, belly, neck and head snugly and physically prevent the midges from feeding. Fly sheets should be put on in March-April, before the horse starts to scratch, otherwise the rug will just get shredded. The fly sheet should be worn all the time, as even though the midges are most active at night they will still be out during the day and it only takes one or two bites if the horse is allergic to set the problem off.

Use the fly sheet continuously until the first cold spell in autumn gets rid of the insects for another year. It’s important to remove the sheet at least once a week and groom the horse to avoid clumps of dead hair and dirt building up on the coat and irritating the skin. This also gives you the chance to assess the horse’s body condition and check for any other problems. A pale sheet reduces heat retention and helps keep the horse cool. The sheets need to be relatively light to make them suitable for use in the summer. This reduces their durability and they may eventually fray or tear. As soon as this happens, they become ineffective and need to be replaced.

Fly control during exercise

Midges are not inclined to bite horses while they are moving, so you can leave the sheet off during exercise. Some sensitive horses may benefit from a fly fringe or face mask/net while being ridden. Apply plenty of fly repellant, especially for slow work, as horses with sweet itch may also be irritated by the bites of horses flies or ‘clegs’ and other nuisance insects. Reapply the repellant when cooling down after work, before replacing the fly sheet once the horse has dried off.

Stable management

Helpful stable management practices include stabling the horse when midges are most active, typically at dusk and overnight, especially during spells of warm, still weather.

Fine mesh covers over the door, windows and air vents keep insects out while still allowing fresh air to circulate. A fan in the stable may create air currents and discourage the weak-flying midges from entering. Avoid turning affected horses out in fields that are close to still water sources and damp ground, where midges can breed.

Reduce the potential for water to collect in stable yards by cleaning water troughs and drinkers regularly, disposing of old tyres and other containers in which rainwater may gather, and filling in potholes.

Midges don’t breed in manure however, so the muck heap is not a problem as long as there aren’t pools of water or run off collecting at its base.

Dietary supplementation with omega-3 and omega-6 fatty acids has been associated with reduced skin allergies in other species, and there is some evidence for its efficacy in horses.

One study found a reduction in the severity of the allergic response when horses with sweet itch were fed 400-500g of flaxseed (linseed) meal daily for six weeks. However, feed supplements alone are ineffective in the management of the condition. Veterinary research is ongoing to try to develop an effective sweet itch therapy or vaccine, but until these become available the mainstay of treatment is going to be to try and stop susceptible horses getting bitten by the midges each summer.

The “armies of the itchy witch” are widespread and persistent, but there are ways in which we can take to protect both horses with sweet itch and ourselves from their unwelcome attention in the summer months. I’d encourage everyone to put a visit to Ballycroy on their post Covid-19 to-do list. You can then see for yourself just how beautiful this part of Ireland is, but make sure to pack the insect repellant and a fly hat for the trip!