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The causes of ticks and fleas on dogs

At this time of year, a parasite review is appropriate

dog scratching

Flea control requires treatment of the dog and the environment

What are the causes of ticks and fleas on dogs and where do these parasites come from? One thing is certain, foreign ticks are bringing new diseases to British dogs.

Tick life cycle


These arachnids have been around for millions of years, feeding on the blood of mammals, birds and reptiles. Famous for spreading Lyme disease, also known as borreliosis (a recent survey showed about 2% of ticks are infected), ticks can also be responsible for fevers, abscesses and previously ‘foreign’ conditions such as ehrlichiosis and babesiosis. Climate change, the removal of compulsory tick treatment when returning from Europe and increased travel have all contributed to the appearance of these nasty diseases. (Read more on Lyme disease and its symptoms on dogs here here.)

tick pupae

Foreign ticks are bringing new diseases to British dogs

Tick life cycle

The life cycle takes around one year to complete. While peak numbers are seen in spring and autumn, I have removed ticks from dogs in every month of the year.

We can begin with an eight-legged adult that, given the right temperature and humidity, climbs up long grass or plants, holds on with its hind legs and waves its forelegs about, looking for a warm, carbon dioxide-emitting host in a process known as ‘questing’. After it has found a victim, it buries into the skin and cuts a hole in it with its hypostome to suck blood.

After 24 hours, the tick will inject an anticoagulant so as to keep the blood flowing. This is when the transference of infection will occur, so rapid removal or use of appropriate treatments is crucial. Adult females then lay eggs on the ground, which hatch into larvae that feed on small mammals and become nymphs, which feed again before maturing into adults.

Adult tick questing

Adult ticks search for a host in a process that’s known as ‘questing’

Terrible tick truths

• The most common tick in the UK is the sheep or castor bean tick, Ixodes ricinus.

• Female ticks can lay around 3,000 eggs.

• The brown dog tick, Rhipicephalus sanguineus, was previously confined to Southern Europe and North Africa, but has been found in Britain. It is a disease-spreader.

• A testing laboratory in Bristol has found tick-borne exotic diseases in dogs that have never been out of the UK.

• Guinea fowl consume massive quantities of ticks and can help control them.

• Ticks that cannot find a host to get a blood meal will die.

• Ticks should not be burnt with cigarettes or soaked in alcohol, as this makes them vomit into the host, increasing the risk of the spread of disease.

• A fully engorged tick will contain about 0.5ml of blood, but will have sucked and regurgitated 15ml of blood to get this 0.5ml. A 20kg dog will have about 1.6l of blood in its circulation.

cocker spaniel

Thankfully, many treatments exist to combat ticks and fleas

Flea and tick treatment

There are some relatively new products that have a one to three-month efficacy and kill fleas, ticks, ear mites, biting lice, demodectic and sarcoptic mange. I am no longer impressed by the efficacy of products that contain fipronil.

life cycle of a flea

Flea life cycle

To control fleas, a good understanding of the life cycle is required. Adult fleas, which are wingless and laterally flattened for easy movement through the hair, live on the dog. Females lay eggs daily. These drop off into the environment and hatch into tiny maggot-like larvae within a week. These feed on detritus, flea dirt (which looks like coal dust) and tapeworm eggs, before moulting twice and becoming pupae. These structures are more robust and very resistant to insecticides, desiccation and temperature change. The adult flea will only emerge under optimal conditions. Proper flea control will require treatment of both the environment and the dog, unless products with lengthy efficacy are used.

Flea pupae

Flea pupae can remain viable for up to two years

Fun flea facts

• There are over 2,500 species and subspecies of flea.

• The most common flea found on the dog is the cat flea, Ctenocephalides felis.

• The tropical rat flea Xenopsylla brought us bubonic plague during the Crimean War.

• A single flea can lay 50 eggs a day. These hatch in one to six days and are adults in three weeks. It doesn’t take long for huge numbers to build up.

• Some, such as the rabbit flea Spilopsyllus cuniculi and hedgehog flea Archaeopsylla erinacei, are host specific.

• Flea pupae can remain viable for up to two years, waiting to be triggered by movement, carbon dioxide in breath and body heat.

• Fleas found on a dog will account for only 5% of the population. The rest will be in the environment.

• Flea larvae can ingest tapeworm eggs (Dipylidium caninum), resulting in adult fleas containing immature tapeworms. These can be swallowed by dogs during grooming, causing tapeworm infections. (Read more on tapeworms in working dogs here.)

You might also like to read “Could my dog catch ear mites from another dog?”