12 – Putting the bite on lice, ticks and mites

The two forms of lice common in New Zealand: (L-R) Haematopinus asini and Damalinia equi
The two forms of lice common in New Zealand: (L-R) Haematopinus asini and Damalinia equi. © Instituto de Ciências Biomédicas

A horse’s coat does a pretty good job of keeping it warm. Little wonder that some critters find hanging out on a horse’s skin much to their liking.

Among them are lice, which are wingless insects. The females lay eggs that stick to the hairs in a horse’s coat.

The young hatchlings are called nymphs and, after two moultings are fully-fledged adult lice. Adulthood is reached in only a few weeks.

Unlike most other parasites, they never have to depart a horse to complete their life cycle.

There are two common forms in New Zealand. The smaller biting louse, Damalinia equi, grows to about 2mm in length and is so named because it feeds on shedding skin and other secretions.

The so-called sucking louse is more properly called Haematopinus asini and, as both its names suggest, it survives by piercing the skin and sucking out blood.

They can occupy any part of a horse but tend to prefer where the coat is thicker, such as along the back, where the tail joins the body, or around the mane.

Lice infestation is usually at its peak in the winter.

It goes without saying that lice can cause skin irritation, leading to rubbing and scratching by the horse.

Insecticides are available to deal with lice, but fortunately the macrocyclic lactones – that’s the family that includes ivermectin and moxidectin – deal with them effectively.

A drenching late in autumn with one of this family should provide your horse with a comfortable winter and the early spring drenching should similarly set your horse up for a good summer.

It’s wise to check your horse from time to time for lice. If they prove to be a problem on your property, make sure you don’t spread them from horse to horse with grooming equipment and treat the linings of your horse covers with a product marketed for the purpose.


Ticks are eight-legged blood-sucking arthropods, which sounds more like an insult than a parasite. In New Zealand, they are most common in the North Island because the climate is more to its liking.

There is only one variety found in New Zealand and, once again, its liking for blood is reflected in its name: Haemaphysalis longicornis.

The adult female tick lays eggs in vegetation and the infective larvae are ready to infect a horse two or three months later. They gather on plants in the hope of catching a ride as a suitable host brushes past.

Once on horse’s coat, they will gorge on blood for about five days before dropping off and, fuelled by all the blood, moult into the next stage. It again sets itself up on vegetation with the intention of catching another ride.

It feasts again, growing to about 6mm in length and at this stage looks to the naked eye like little black beads. The adults will most likely be found during the summer months.

Once brimming with blood, they drop off to lay eggs and begin the life cycle again.

Ticks are likely to be a problem only where climate and vegetation are to their liking. They generally cause little in the way of skin irritation although some horses do have a severe local reaction to bites.

It’s worth making a visual check of the ears of horses as this is prime real estate for ticks. The most likely spots for tick infestation centre on areas most likely to brush past vegetation – the legs and underside are most vulnerable.

An insecticidal spray or wish is usually only necessary in the unlikely event a horse has a heavy infestation. Otherwise, if you see them, squeeze the skin around them and pull them out – mouth and all – with a pair or tweezers or even your fingernails. Get your nails or the tweezers underneath them and pull, to ensure you get the mouth parts out.


Mites are like tiny ticks – you need a microscope to see these little arthropods – and can live out their entire life on one animal and reproduce to their heart’s content, making the occasional transfer to a new host by direct contact.

The mite known as Chorioptes tends to hang out in the lower legs and cause what horse owners cause mange: irritated areas of skin that can become inflamed and scabby.

This mange can spread up the legs and even on to the belly.

Secondary bacterial infection is an ever-present risk with mange.

It’s best to consult a veterinarian as there are several causes of mange-like symptoms. A vet needs to identify the correct cause so proper treatment can be implemented.

If the vet confirms mange caused by chorioptes, treatment is likely to involve regular washes with an approved insecticidal wash until the condition improves.

Another mite that can cause problems is Psoroptes, which hang out in ears. Most horses show only very mild symptoms but in more severe cases there may be swelling at the base of the ears. A horse may rub its ears in an effort to gain relief from the irritation or carry them in an unusual way.

Again, a vet’s attention is required as there are several potential causes of ear irritation, including potentially serious bacterial infections.

If the vet finds the problem is caused by Psoroptes, they are likely to prescribe insecticidal ear drops.

In all cases, only use insecticidal preparations approved for use on horses.

» Next: Here’s the rub about pinworms

First published on Horsetalk.co.nz in February, 2009




Latest research and information from the horse world.

Leave a Reply

Your email address will not be published. Required fields are marked *