Fleas on Dogs: How to Spot Them, Treat Them and Break the Cycle

You found one flea. The question that follows is how many you can't see.

The fleas on your dog are the smallest part of it: only about one in twenty is actually on them. The rest are eggs, larvae and pupae in your carpet, bedding, and the shady patch of dirt they nap in outside.

That's why only treating your dog rarely works, and why you'll keep finding fleas for weeks after you start.

I'll take you through how to be sure it's fleas, how to treat your dog and the house together, and which products can help.

Flea dirt is the most reliable sign, because it stays in the coat long after the fleas themselves have moved.

Flea dirt is flea droppings, and it is mostly digested blood. It looks like coarse ground pepper scattered close to the skin. 

The test is simple: comb some onto a damp piece of white paper towel and wait a few seconds. Ordinary dirt stays dark. Flea dirt spreads into a rust-red bloom, because it is blood.

Look where fleas prefer to feed and where your dog cannot easily groom. The base of the tail is the classic spot, along with the groin, the armpits and the belly.

Other signs worth knowing:

• Scratching, biting and licking that concentrates on the back half of the body
• Scabs and thinning hair along the back and tail base
• Restlessness, or sudden bursts of chewing at one spot

You may never see a live flea, particularly on a dog that grooms well or one that is allergic. Absence of visible fleas is not absence of fleas.

Treat every pet in the house with a registered flea product on the same day, then treat the home itself. Expect three to six weeks before you stop seeing fleas, and up to three months before the household is genuinely clear.

1. Start with a registered flea product

Use a veterinary flea product suited to your dog's weight and age, which is how our dog flea treatments range is sorted. Modern oral chews and spot-ons kill fleas within hours and keep working for weeks to months, depending on the product.

• NexGard is monthly and Bravecto stretches further between doses. 

• If your dog will not take a tablet, Advocate is a monthly spot-on that also covers heartworm, roundworm, hookworm, whipworm and the oesophageal worm, though not ticks or tapeworm.

• Seresto is a collar for dogs that are hard to dose on a schedule.

2. Applying a spot-on correctly

Part the coat between the shoulder blades until you can see skin, and apply the liquid onto the skin rather than the fur. Empty the whole tube, and keep your dog dry for 48 hours. Stop other pets licking the site until it dries. A spot-on applied to fur instead of skin is a common reason a treatment appears not to work.

3. Treat every pet at once, cats included

An untreated animal in the house is a breeding site. The fleas on it lay eggs into your carpet every day, and those eggs become the next wave that lands on everyone, so treating one dog in a two-pet house only slows the cycle down. Use a product registered for each species, so the cat goes onto something from our cat flea treatments range. Never put a dog product on a cat.

4. Treat your home

This is the part people skip, and it is where most of the fleas actually are.

• Vacuum daily for the first fortnight, including under beds and furniture, along skirting boards, and the car if your dog travels. Empty the vacuum into an outside bin each time.
• Wash all bedding, yours and theirs, at 60°C. A hot dryer cycle helps as much as the wash.
• Do not forget the spots that are not obvious: the dog's favourite shady patch outside, the couch, and the boot of the car.
• Keep it up for several weeks. One thorough clean will not do it.

Vacuuming does more than lift eggs and larvae. The vibration and warmth prompt pupae to hatch, which brings them out of their protective casing and into contact with the product on your dog. Studies of treated dogs in simulated home environments show this is how a product on the animal eventually clears the flea stages living in the house.

Where baths and combs help, and where they do not

A flea bath kills the fleas on your dog at that moment and does nothing about the ones in the house or the ones that hatch tomorrow. It is a comfort measure, not a treatment. A flea comb is genuinely useful for confirming fleas and for puppies too young for medication, but it will not clear an infestation.

If you are bathing anyway, our guide to dog shampoos covers what suits itchy or sensitive skin.

A flea goes from egg to adult in as little as two to three weeks, and only about 5% of a flea population is on your dog at any moment.

That 5% figure is the single most useful thing to understand about fleas. The adults you can see are the small visible part of a much larger population living in your house.

Here is what the other 95% is doing.

Eggs. An adult female starts laying within a day or two of her first meal and produces around 50 eggs a day. They are smooth and not sticky, so they roll off your dog and land wherever they happen to be sleeping and walking.

Larvae. The eggs hatch into small larvae that avoid light and burrow down into carpet fibres, cracks in floorboards, soil and bedding. They feed on flea dirt dropped by the adults above them.

Pupae. The larvae spin a sticky cocoon. This is the problem stage. The cocoon is resistant to insecticides and to almost everything else, and the flea inside can wait for months for a signal that a host has arrived: vibration, warmth, carbon dioxide.

Adults. They emerge, find a host within hours, and start the cycle again.

In warm humid conditions the whole loop can run in two to three weeks. In a cool house it stretches out considerably, and the pupae simply wait.

This is why clearing an infestation takes three to six weeks rather than three to six days, even when you do everything correctly. You are not waiting for a product to work. You are waiting for a reservoir of protected pupae to finish hatching into the treatment you have already applied.

A dog that swallows a flea while grooming can pick up tapeworm, so flea control and worming work as a pair rather than as separate jobs.

The mechanism is straightforward. Flea larvae in the environment eat flea dirt, and in doing so they can swallow tapeworm eggs. Your dog then bites at an itch, swallows the flea, and the tapeworm matures in the gut.

What you notice is small pale segments that look like grains of rice, moving near the tail or dried onto bedding. They are the tapeworm shedding.

An all-wormer such as Drontal, given alongside the flea product, is the usual way to cover the gap, and our dog worming treatments range sets out what each one treats. Our guide to intestinal worms in dogs sets out what each product class actually covers.

New fleas keep appearing for weeks after correct treatment, because the pupae in your carpet were never reachable by the product on your dog.

If you have treated properly and are still finding fleas at week two or three, that is the expected pattern rather than a failure. Each newly hatched flea jumps on, feeds, and dies from the product your dog is carrying. You are seeing the tail end of the reservoir emptying.

That said, treatments do genuinely fail sometimes, usually for one of these reasons.

• A pet in the house was missed, or is on a different schedule.
• The dose was wrong for your dog's weight. Estimating rather than checking is common.
• A spot-on was applied to a recently bathed dog, or the dog was bathed too soon afterwards.
• The product was out of date, or stored somewhere hot.
• The house was never treated, so the reservoir is still full.

If none of those apply and you are still finding live fleas after two months of consistent treatment, speak to your vet rather than simply switching brands.

See a vet if your dog is still itching after the fleas are gone, or if a puppy or small dog is pale, weak or lethargic.

Most flea problems are handled at home, but three situations are worth a call.

Flea allergy dermatitis. Some dogs are allergic to flea saliva, and for those dogs a single bite triggers days of itching. This is why the itchiest dogs in the clinic often have the fewest visible fleas, and why owners of those dogs are frequently certain fleas are not the cause. Treatment usually needs prescription relief for the itch alongside strict flea control. Our guide to skin conditions in dogs covers how flea allergy dermatitis is diagnosed and what else produces the same itch.

Skin infection. Persistent scratching breaks the skin. Hot spots, weeping patches, a smell or crusting all need veterinary treatment rather than another flea product.

Anaemia. Heavy flea burdens take enough blood to matter in puppies, small dogs and elderly dogs. Pale gums, weakness, rapid breathing or collapse need same-day attention.

Flea prevention runs all year for most Australian dogs, and a heated house keeps the cycle going through a southern winter.

Season and climate by region

In Queensland and northern New South Wales, conditions suit fleas more or less permanently, and there is no off season. Further south, numbers climb from spring and peak through summer and early autumn.

The catch in cooler states is indoors. Heating keeps a house at exactly the temperature flea eggs and larvae prefer, so a winter break in prevention often produces a surprise infestation in a home that felt too cold for it. Our guide to year-round parasite prevention across Australia maps this by region.

Choosing a product for your household

Oral chews are given by mouth and cover one to three months depending on the product. Spot-ons suit dogs that will not take a tablet, though water can shorten their life. Collars run for months and suit dogs that are hard to dose. Fast-acting tablets like those in the Capstar range kill adult fleas within hours. They are useful at the start of an infestation, but they have no lasting effect and are not a prevention plan.

If ticks are also a concern where you live, a combined product usually makes more sense than two separate ones, and our all-in-one dog parasite protection range is where those sit. Our guide to paralysis ticks on dogs covers which products cover both.

If you have cats in the house

Some dog flea and tick products contain permethrin, which is safe for dogs and can be fatal to cats. A cat does not need to be treated with it to be harmed. Grooming a recently treated dog, or sleeping against one, is enough. Choose a dog product without permethrin, or keep the animals apart for 48 hours after treating the dog. That is the manufacturer's own advice, and it is longer than the product takes to dry. Our guide to fleas on cats covers what is safe for them, and why indoor cats get fleas too.

Why overseas advice often misses here

A lot of the flea advice online is written for the northern hemisphere, where the season is short and the product range is different. Some products recommended in those articles are not sold in Australia, and some carry actives that are a poor fit for a household with cats. Check that anything you buy is registered for use in Australia and for your dog's weight and age.

If the choice is what is holding you up rather than the method, our guide to the best flea, tick and worm treatments for dogs sets the main options side by side on weight range, what each one covers, and how often it is due.

Two of them come up more than any others: NexGard Spectra vs Simparica Trio compares the two all-in-one monthly chews most Australian dog parents end up choosing between.

If you are in the middle of an infestation right now, the thing worth holding onto is that the timeline is normal. Consistent treatment and cleaning clears almost every case, and seeing fleas in week three does not mean it has not worked. After that, prevention is a smaller job than the clean-up ever was. 

Our guide to the best dog flea, tick and worm treatments covers how fleas fit alongside ticks, worms and heartworm in one plan.