Quick A to Z of common external parasites in dogs

Estimated Reading Time 6 minutes
Quick A to Z of common external parasites in dogs

Read our article for a handy overview of parasites that are usually found on a dog's skin.

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Common external parasites of dogs


Fleas are the most common type of external parasite of the dog, and the most common type of flea found on both cats and dogs is the cat flea (Ctenocephalides felis). Fleas are small wingless insects that live on the coats of dogs, and they can live for up to 2 years!

Female fleas take a blood meal from the cat (bite them), and then lay their eggs - which can be up to 50 eggs per day! The eggs fall off the cats’ coat and remain in the environment (the home) until they hatch and become larvae, which can be as little as 2 days.

The larvae feed off the flea dirt (which is flea poop) and remain in bedding, carpets and cracks in the flooring where they lodge themselves deep down as they dislike light. They can lay dormant for up to 2 years only reactivating in response to vibrations, temperature and the presence of carbon dioxide which all indicate a person or animal is nearby to jump onto once hatching.

Signs of fleas include scratching, finding flea dirt in their coat or where they sleep and seeing live fleas. Fleas can also transmit one species of tapeworm to dogs, so you may see signs of tapeworm on top of the faeces or crawling around your dog’s bottom (they can look like grains of rice).

Read more about managing fleas in dogs here.

Demodex mites

Demodex mites live in the hair follicles of all dogs. Usually their immune system keeps the mites in check and the mites never cause an issue. However some dogs' immune system can fail with regards to keeping the mite numbers low, and this can allow them to rapidly multiply causing severe skin disease in the affected dog. It is more common in younger dogs, but adult dogs can also suffer. Symptoms of demodex mites include itching, hair loss, crusting/scaling of the skin and dark thickened skin.

Sarcoptic mites

These microscopic round mites bury into dogs’ skin where they feed on the material in and on the skin. They also lay their eggs in the tunnels they leave when they burrow into the skin. The mites’ activity causes intense itching for the dog. They will chew and scratch constantly which leads to hair loss and eventual thickening of the skin. They can also get secondary infections from the itching. Sarcoptic mites are ZOONOTIC which means they are transmissible to humans. They cannot live on human skin for long, but will cause severe itching until the mites die. It is also very contagious to other dogs.

Ear mites

Otodectes cynotis aka ear mites are just barely visible as tiny white dots to the naked eye. These mites live inside the dog’s ear canal and feed on wax and debris where they cause a lot of irritation and inflammation. They are passed on through close contact with infected dogs but can also be acquired from the environment.

Signs include scratching at the ears, crusty discharge in the ear, head shaking, red painful ears and in some cases an aural haematoma (blood blister of the ear flap). All of these signs can also indicate an ear infection.


There are two types of lice that affect dogs in the UK - the sucking louse (Linognathus setosus) and the biting louse (Trichodectes canis). They spend their entire lives on the dog and can only survive in the environment for a few hours. The biting louse can be very irritating to the dog and can also pass on the tapeworm Dipylidium caninum. The sucking louse feeds to the dogs’ blood and can cause issues when present in high numbers as they can cause anaemia.

Lice infestations tend to occur in areas where dogs are in crowded, unclean conditions and they tend to target young, elderly or malnourished dogs.

Luckily lice infestations are quite rare in dogs in the UK, but signs to look for include visible “nits” in their fur or visible adult lice, itching, patchy hair loss, skin sores and anaemia.


Ticks are grey-brown, 8 legged parasites that bite your dog and feed on their blood. They are quite small initially but swell up to the size of a pea once they become engorged with your dogs’ blood. There are several species of tick found in the UK, with the most common being Ixodes ricinus. Ticks will affect a lot of different animals including dogs, cats, sheep, hedgehogs and even humans to name a few.

Ticks are found in long grasses and woodland, where they crawl onto the long grasses and wait for an animal (or human) to walk past where they can attach themselves. Ticks can transmit diseases such as Lyme disease to dogs through their saliva when they bite. With an increased number of dogs entering the UK from Europe, there is also the risk that some exotic tick species are being introduced to the UK, along with diseases such as Babesiosis.

Finding ticks is relatively easy once they have fed and are engorged as they appear as small grey / brown swellings or lumps and are more common on the head / face and legs. They can be removed using a tick fork but care must be taken to not leave the mouthparts in.

Flystrike (Myiasis / maggots)

Not very common fortunately but still something to be aware of in dogs. If your dog has an open wound, urine scalding or soiling of their fur, this can attract the interest of flies more commonly in the summer months during warm weather. Flies will lay their eggs on the dogs’ fur or in their wounds and the eggs appear as small flecks or grains on the fur. The eggs then progress to the larval stage which is maggots. Maggots can cause a lot of tissue damage and urgent treatment is required in cases of flystrike - it can be life threatening. Prevention includes keeping your dog as clean as possible during cases of diarrhoea and soiling, as well as getting wounds treated and cleaned and monitoring them several times a day.

Many of these parasites can be prevented with appropriate measures, and what treatments are advised is dependent on your dogs’ risk factors and lifestyle. Remember it's important to check your dog regularly for signs of external parasites as no product is 100% effective, particularly tick prevention

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This article was written by Amy Everden RVN, CSQP, ISFM CertFN. Amy is a registered veterinary nurse (RVN) who has worked in a variety of first opinion and 24 hour veterinary hospitals. In 2019 she completed her certificate in Feline Nursing with distinction.

Published: 24/02/2022
Last updated: 01/04/2022

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