February 19, 2024 | General

Beginner’s Guide To Fleas in Pets

At the mere mention of the word “flea”, most of us will find ourselves subconsciously scratching, imaging the little critters crawling over our skin, and derogatory phrases such as “flea-ridden” or “flea-bag” automatically spring to mind…but how much do you actually know about fleas?

Well, in this blog, we shall attempt to both inform and myth-bust in the hope that we will end up thinking of the flea as not just an unwanted parasite, but as quite remarkable creatures in their own right.

Vet checking for fleas on a dog

What are fleas?

Flea is the common name for the order Siphonaptera, and there are 2,500 species (!) of these small flightless insects that live as external parasites of mammals and birds and live by ingesting the blood of their hosts. Fleas have been around since at least the Middle Jurassic period and probably originated in mammals first before moving on to inhabit birds too.

What do fleas look like?

Adult fleas grow to about 3mm long and are usually brown, with bodies that are “flattened” sideways allowing them to move through their hosts’ fur or feathers. They do not have wings and their hind legs are extremely well adapted for jumping. They have claws to keep them from being dislodged and their mouthparts are adapted for piercing skin and sucking blood.

What is the life cycle of the flea?

Flea Life Cycle

Fleas go through 4 life stages as shown in the diagram above. In most species, neither male nor female fleas are fully mature when they first emerge from the pupa stage but must feed on blood before they are capable of reproduction. Some species breed all year round whilst others synchronise their activities with their hosts’ life cycles, or with the climate/environment they find themselves in.

Only 5% of the life cycle is spent as an adult flea, meaning that controlling flea populations has to take into account the fact that 95% of a flea’s life is not spent living on its host animal or bird, but in the immediate environment.

The number of eggs laid by a female flea depends on the species with batch sizes ranging from 2 to several dozen. The total number of eggs produced in a female’s lifetime varies from one hundred to several thousand, and each egg takes from 2 days to 5 weeks to hatch. That is A LOT of fleas.

Under ideal conditions of temperature, food supply and humidity, adult fleas can live up to a year and a half and completely developed adult fleas can live for several months without eating so long as they do not emerge from their puparia. The optimum temperatures for the flea’s life cycle are 21-30℃ and the optimum humidity is 70%. This is why we often see fleas in our pets in the Spring and Autumn, as the central heating gets switched on, creating the ideal environment for the fleas to survive and reproduce in.

How do I tell if my pet has fleas?

Fleas are external parasites, living in the body hair, or fur, of their hosts and it is possible for many species of flea to infest more than one host species. In fact many fleas found on dogs are actually of the cat species.

Signs that your pet may have fleas include the following:

  • Scratching

  • Areas of fur loss, or bald/sore patches

  • Spots, redness or irritation

  • Tiny dark specks of flea “dirt” (faeces) in the fur

  • Small brown-black insects scurrying about in the fur

  • Unexplained insect bite marks on yourself

Regularly grooming your pet with a fine-toothed comb held over something white such as a piece of kitchen roll is also a good way of checking for fleas and any fleas or flea “dirt” will be deposited on the surface. When a few drops of water are applied, if the droppings turn reddish/brown in colour, your pet does likely have fleas.

How can I treat fleas?

As explained above, fleas can live in the environment for a long time, and hence promptly treating your home as well as your animals is essential to get things under control in the event of an outbreak.

Always ensure you use a treatment product on your pet that is suitable for THAT pet - and treat all pets in the household. To treat the environment, a suitable household spray such as Indorex Household Spray should be used, carefully following the directions on the packaging, and always apply to soft furnishings after thoroughly vacuuming them first as the vibrations from this will help bring the fleas or eggs up to the surface. Then throw the dust bag from your vacuum away after each use to prevent any flea eggs and larvae from developing.

Wash all animal bedding on a high degree in the washing machine, and be sure to treat your cats and dogs for worms too, as the life cycle of the flea and the tapeworm is closely interlinked.

What are Flea bites?

Some animals will suffer from a hypersensitivity reaction to flea saliva, and this requires prompt veterinary treatment to relieve the irritation and discomfort caused by the scabs that form in the affected animal 

As fleas feed off the blood of their host, young and frail animals can become very weak and debilitated through blood loss leading to anaemia - this can even be fatal in severe cases

Fleas can also pass diseases to your pets. For example, myxomatosis is a serious disease in rabbits which can be spread by fleas.

Comment from PocketVet vet Dr Rachel Louise Keane. BVSc BSc MRCVS

Ultimately, prevention has to be better than cure and as a general rule, prescription flea treatments work more effectively than over-the-counter versions. Where there is an active flea problem, treat all animals in the household with suitable products - DO NOT BE TEMPTED TO USE DOG FLEA TREATMENT ON A CAT as many contain permethrin, a chemical which is highly toxic to cats; be sure to treat the environment too. Be vigilant - regularly grooming your pets means that any infestations can be spotted early on, and dealt with promptly and efficiently.

Medically reviewed by:


How To Get Rid of Fleas | RSPCA

Pest advice for controlling Fleas (bpca.org.uk)

Understanding the Flea Life Cycle | PetMD

Fleas Life Cycle – How to Break It? - FleasControl.com

Fleas | Dog health | The Kennel Club