Introducing fleas and worms

Written by Kate Bendix – Author of My Itchy Dog & The Dog Diet 

Fleas are disgusting! They suck up to our pets – stealing blood, spreading disease, laying eggs, making new parasites by the thousand and leaving them all over the house. Immature fleas give your dog tapeworm as well.

Worms are no better, they’re inherently lazy, their eggs grow up to be worms who leech off your dog; mostly by hanging off the gut wall, eating passing food then shunting their own eggs out into the world via your dog’s poo.

Parasites, quite literally, suck!

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Fleas are an obligate haematologist parasite meaning they must feed on blood to survive, just like a cat is an obligate carnivore who needs to eat predominantly meat or fish.

Most of the fleas you’ll find pimping off your dogs are actually cat fleas. They have flatter heads, all the better for moving swiftly through a dog’s fur. Fleas are opportunists, they’ll jump on to any mammal if there’s a free blood meal going and if they can get a two-for-one deal by laying eggs on their host at the same time, then so much the better.


How do you know when your dog has fleas?

It’s recommended you check your dog and cat regularly for signs of Fleas. If they have them you may see flea dirt (like black dust) or if you are lucky enough you may see a real adult flea jumping about on them! Other signs to look for are when you find them chewing their paws and pads, scratching at the groin area, armpits, belly, or under the chin where they lie down. Or, of course, if you get bitten!

What you need to know is that for every flea you spot on your dog or cat there are estimated to be at least nine more elsewhere, in your house, at various stages of development, and that you will have to treat the whole house to make sure they’re all dealt with. Prevention is way easier to deal with than infestation. For advice on how to do this, see our blog.


How does a dog get fleas?

A female flea will jump onto your dog, have a blood snack and lay 50 eggs a day in a cluster normally at the base of the hair.

Flea eggs are white and a bit smaller than a grain of rice. The eggs get shaken off as your dog goes about his business to land on the carpet, his bed (or yours!), and in between floorboards. In a few days or weeks, depending on the outside temperature, the eggs hatch into larvae.

The larvae move along using tiny hairs on their bodies, finding food – dirt, flea faeces and dust – which as we know is mostly human skin: is yours crawling yet? When they’re large enough, they spin themselves into a protective cocoon to develop into an adult, just like a moth or a butterfly, where they wait. And wait. And wait. Until it’s ‘time’. While the adult flea is tucked up in its cocoon everything is rosy. It can hunker down there for months, or even years, until the conditions are right for it to hatch to maximum effect.

The adult flea only emerges if it’s pretty certain there’s a host close by. It detects this by vibration, changes in temperature or even changes in carbon dioxide levels as your pet breathes into the carpet or flooring.

Now you have a new batch of fleas which jump on to your dog and the whole process can start all over again.


Immature fleas carry tapeworm

When they’re at their larval stage, a flea will eat a tapeworm egg pouch if it comes across one. This sac contains around 50 tapeworm eggs. When the flea matures into an adult the tapeworm eggs also mature. The newly hatched flea finds a dog to jump onto, the dog licks the itch, ingests the flea, the tapeworm eggs release and that’s that, your dog now has tapeworm!



Worm eggs need to be eaten by your dog in order to develop into larvae, then worms. The newly hatched worms live inside your dog and release millions of eggs through the dog’s faeces which goes back into the soil, or lingers on the ground waiting to be licked up by another dog and the cycle continues. That’s the long and short of it.

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Lungworm eggs enter the same way but move from the gut into the bloodstream to sit by the heart where they hatch. The lungworms release millions of eggs which break into the bottom of the lungs then make their way up from bottom to top. The dog coughs them up, swallows them back into the gut where the eggs pass out, blinking into the daylight to wait for another hapless creature to ingest so the cycle can begin all over again.

Lungworm can be fatal if left untreated.


How does a dog get worms?

Worm eggs live in faeces and soil, on dead animals, in snails and slugs, on grass, paths, in water bowls and toys, anything found or left outside.

Your dog eats or rolls in contaminated faeces (it can be dog, cat, fox, any poo will do); licks or eats grass; eats a slug, though God knows why; drinks from a bowl, plant saucer, puddle; sniffs, licks or eats a dead animal or bird and they’ve likely ingested or inhaled a variety of worm eggs. Dogs are, indeed, disgusting creatures.


Puppies get worms through their mothers milk too!

Even if a bitch has been wormed as normal up to and after whelping she can still pass roundworm on to her puppies through her blood, and milk. It is essential a puppy is wormed every two weeks (or as per a veterinary schedule) until they’re 16 weeks old using a pharmaceutical wormer. After that they can be moved over to a natural repellent with an overlap.


Worm types

The most common types of parasitic worms found in dogs in the UK are roundworms (the Toxocara roundworm being the most common type by far) and tapeworms.


Roundworms are white and can grow to several centimetres in length, resembling bits of string, whereas tapeworms are flat, like segmented linguini. Tapeworms can grow to 50cm long.


Both live in the intestines and have been known to share space with a couple of other creatures: hookworm and whipworm, though these are not nearly as prevalent in dogs in the UK


Watch our flea & worm Q&A video here