The deer louse fly – annoying insect for horses and humans

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The deer louse fly is often mistakenly referred to as the ‘flying tick’. If you like riding out in woodlands in summer or early autumn, you can be literally chased and attacked by swarming deer louse flies. In some locations, this parasite is so widespread that at the peak of their life cycle, riding near the forest can even become dangerous. Some people report that their horses panic when being attacked by the deer louse fly. The deer louse fly is still not that well known in England and in some areas hardly noticeable. However, due to climate change and milder winters, it is on the rise.

Occurrence of the parasite

The deer louse fly (Lipoptena cervi) aka deer ked is a fly from the louse fly family (Hippoboscidea). In contrast to the tick, which sits on bushes and tall grasses and waits for passing animals or humans, this parasite attacks its host from the air. Louse flies are an independent family of blood-sucking flies. There are many different species of this genus, including the horse louse fly (Hippobosca equina), which differs from the deer louse fly in only a few characteristics. Both infest not only their namesake, but also similar, rather large animals such as cattle, horses, deer, roe deer, but sometimes also dogs or humans.

With a body size of around 6 mm, louse flies are somewhat reminiscent of a fat housefly. They have a stocky, brown to black body with 6 very strong legs, which are equipped with large hooks at the ends to get a good grip onto the animal. After reaching their host, the females of the deer louse fly shed their wings and continue to live as a louse on the host’s body. It is assumed that the horse louse fly keeps its wings and can therefore change its host again.

The females of the deer louse fly lay their larvae on the ground, where they stay throughout the winter, hatching the following year and develop into the adult, parasitic stage in autumn. The larvae are relatively sensitive to frost, with only a few surviving in very frosty cold winters, whereas after mild winters an extremely large number of new louse flies are on the move the following year. Therefore, the deer louse fly can spread further and further in our country as a result of climate change, as mild winters become more frequent and long periods of frost become rarer.

The stings of the deer louse fly are painful

After reaching the host, they crawl very quickly through the fur to hook on to a suitable spot and bite. They now live on the host’s skin and feed on its blood by repeatedly biting. An infestation with deer louse flies is usually very unpleasant for the animal, but reactions vary greatly from horse to horse. The bite is extremely painful, sensitive horses in particular show very strong reactions, often they keep looking around, become restless and in some cases can display panic or violent reactions. Especially if the horses have been attacked by deer louse flies in the past, they can have real panic attacks when getting bitten, this can result in an accident for horse and rider. Horses often remain nervous once they return from the woods, scratching and biting at the site of the bite. The pain caused by the bite can turn into severe itching, swelling and develop into a hard welt, there also is a risk of infection.

The bacterium Bartonella schoenbuchensis, which many louse flies carry, is probably responsible for the often-severe inflammation around the bite site, which can spread to form extensive dermatitis. The Central Commission for Biological Safety (ZKBS) classifies B. schoenbuchensis as a zoonotic pathogen. This is the name given to pathogens that can be transmitted from animals to humans, but also vice versa.

On horses, the louse fly usually hides under the mane or at the base of the tail. The bites can also occur in the elbow area or between the hind legs. Upon the return from the woods, if the horse starts shacking their head excessively or kicking out with the back legs in an attempt to rid itself of an insect and thorough inspection underneath the mane and tail dock should be undertaken. Be aware the deer louse fly is a very agile crawler and as soon as the light falls on it, the deer louse fly will very quickly go into hiding by burying its body into the fur, mane or tail.

Can you ward off deer louse flies?

So far no effective prophylaxis has been found. The fly sprays on the market claiming to deterrent ticks, mosquitoes, horse flies and other insects have unfortunately not found to be effective against the deer louse fly. Even fly rugs do not provide reliable protection against an infestation: the louse is able to simply crawl underneath.

Only permethrin (commercially available emulsion for horses) seems to have an effect and is often used in the New Forest in the south-west of England, as the horse louse fly (Hippobosca equina, also known as ‘crab fly’), which is extremely widespread in this area, it makes riding practically impossible in summer and autumn. However, as permethrin is a powerful insecticide, the usage should be carefully considered, especially as it is usually only for a short period in late summer or autumn that horses are being plagued by the crab fly when riding out in the forest.

Conclusion

As there is no reliable defence to deterrent these insects and protect the horses from their bite, it’s even more important to be pro-active in prevention and aftercare. It’s best to avoid large areas of woodlands when the deer louse fly is most active. Deer louse fly does not like open spaces, therefore will not target horses or riders in open spaces such as surfaced arenas or open fields – away from the woods. If you are riding near wooded areas where the louse fly is considered to be widespread, you should dismount early during the ride if there are any signs of the horse being unsettled and examine your animal thoroughly. Out on pasture horses that appear nervous and restless for no apparent reason should be examined thoroughly. Be mindful that a stressed horse is in ‘flight or flight mode’ and can suddenly kick out or turn round and bite.

Once they drop their wings, deer louse flies are very agile and are difficult to grab with bare hands. They are experts in hiding in the horse’s fur, so search carefully by parting the fur so you can reach down to the skin, especially important if your horses has a long coat. Often as a last resort, a shower with sufficient water pressure is the only option. Once you located a deer louse fly, you will find them just as difficult to kill as ticks. A screw-top jar with some surgical spirit can be used to drown the parasites. If you are out riding and don’t have a jar to hand, you have no option other then squash it, use two stones or your fingernails to do so. The same approach as commonly used in killing house flies won’t work on these tenacious pests.

Tip: if you see the louse fly, quickly fix it with a wide adhesive tape and then remove it.

Bite marks should be well disinfected to avoid any infection spreading, best to monitor closely. If an infection does take hold, call your vet to avoid further development.