Flea Season

When people talk about flea season, they usually mean the warmer months when fleas are most active outdoors. But the reality is more complicated, and understanding it can save your pet a lot of discomfort.

Fleas are tiny, wingless insects that survive by feeding on blood. The species most likely to bother your dog or cat is the cat flea (Ctenocephalides felis), which despite its name is the most common flea on both cats and dogs across Europe. Adult fleas live on your pet, but the eggs they lay fall off into carpets, furniture, and bedding within hours. Those eggs hatch into larvae, which eventually spin cocoons and wait. Inside those cocoons, pupae can lie dormant for months, sometimes up to a year, until they sense vibration, warmth, or carbon dioxide that signals a host is nearby.

In Central Europe, outdoor flea activity typically runs from March through November, with numbers peaking between July and October. Freezing temperatures kill adult fleas and larvae outdoors, which is why winter used to bring natural relief. But that relief is much less reliable than it once was, because modern central heating keeps indoor spaces warm enough for fleas to complete their life cycle all year round.

This is why the traditional idea of a "flea season" can be misleading. A home heated through the winter provides perfect conditions for flea development regardless of what the weather is doing outside. A single female flea can lay 40 to 50 eggs a day and up to 2,000 in her lifetime. In warm, humid conditions, the whole cycle from egg to adult takes as little as 12 to 14 days. The adults you spot on your pet are only about 5% of the total flea population in an infested home; the other 95% exists in the environment as eggs, larvae, and pupae.

Fleas are not just a nuisance. Their bites cause intense itching, reddened skin, and hair loss. Many dogs and cats develop Flea Allergy Dermatitis, the most common allergic skin condition in pets, triggered by flea saliva. In heavy infestations, especially in puppies and kittens, the blood loss from feeding fleas can cause life-threatening anaemia. Fleas also carry diseases: they can transmit Bartonella, the bacteria behind cat scratch disease, and Rickettsia felis, and they act as intermediate hosts for the tapeworm Dipylidium caninum, which pets swallow during grooming.

Because so much of the flea population lives off the animal, treating the pet alone rarely solves the problem. Eliminating an established indoor infestation typically requires at least three months of continuous treatment for every pet in the household, combined with regular vacuuming and washing of pet bedding. It is also critical never to use a dog flea product on a cat, as ingredients like permethrin are highly toxic and can be fatal to felines. Even when you cannot see adult fleas, an infestation may still be present: cats and dogs groom fleas off their coats efficiently, so your vet may check for flea dirt using a damp paper towel instead.

Given how quickly fleas reproduce and how adaptable they have become to indoor living, many veterinary organisations now recommend year-round preventive treatment for all dogs and cats, regardless of how much time they spend outdoors. Your vet can help you choose a product that is safe and appropriate for your pet's species, age, and lifestyle.