Hidden housemates: big fleas, and their little fleas

Itchy? Maybe not, but your cat or dog might be. If you live in any of the major coastal cities in Australia, you are no stranger to a scratching dog or cat. You can blame fleas, or more specifically their bites and saliva, to which your pet is hypersensitive.

Did T. rex have fleas?

Fleas are marvellous creatures! They are ectoparasites (parasites that live outside their hosts' bodies), exploiting their hosts both by using them for nutrition and to stay well protected from the harsh outside environment beyond their host’s fur.

Big fleas even have little “fleas” of their own as well, but more on that a little later. I borrowed the headline from a book by Robert Hegner, who in 1938 used superb illustrations and narratives to explain the world of parasitology. This in turn is perhaps derived from the nursery rhyme, The Siphonaptera (the group of insects to which fleas belong):

Big fleas have little fleas, Upon their backs to bite ‘em, And little fleas have lesser fleas, and so, ad infinitum.

There are about 80 different flea species in Australia and more than 2,000 globally. Even birds have their fleas, and because birds are essentially dinosaurs, I pose the question: was Tyrannosaurus rex feeling that flea bite, too?

When did fleas start living with us?

The dog is man’s closest companion and the cheeky cat a close second. When this relationship was forged, and up until very recently, we shared our human fleas with the dogs and cats, and vice versa. Human flea male and female (Pulex irritans) Jan Slapeta

With better sanitation and improved housing conditions, the human flea has essentially disappeared from Australia. This left a duel between the cat flea and the dog flea. The clear winner is the cat flea that now dominates Australian cities and is the primary culprit behind the itch which commonly afflicts cats and dogs.

Dog on the left and cat flea on the right. Jan Slapeta

The cat flea is so successful because the cities, houses and in fact Australian climate is just perfect for this parasite. The cat flea could not ask for more.

The cat flea adults are blood-sucking, so they stay on the dog or a cat (or even us!). Their immature eggs drop on the ground where they develop into larvae. These larvae need sandy soil, 80% humidity and 25℃ warmth – pretty close to what we enjoy on a daily basis in many parts of coastal Australia.

Cat flea larvae measure around 4 mm and may be crawling all over your sofa! Jan Slapeta

Fleas evolved through the millennia to drink blood and produce large number of eggs. Each adult female can produce around 40 eggs a day. That is a lot of eggs if your pet has just 20 adults and half are females. It adds up to 400 a day and 12,000 in a month! What’s more, 20 fleas is not that many for an Australian dog; some dogs or cats harbour hundreds of fleas.

Fleas are bloodthirsty creatures, but their digestive tract cannot use all the blood and so much of it comes out as dried faeces (“flea dirt”).

This dried blood drops into the animal fur and further drops wherever the animal spends most time. Maybe your sofa, maybe your carpet. That is exactly where eggs drop as well. The larvae that hatch from the eggs are surrounded by pieces of dried blood - their daily meal. The adult fleas thus feed not only themselves, but also their offspring.

It is nice to live with humans. We provide the perfect niche not just for our pets but also their fleas.

But back to our T. rex. Interestingly, the most recent analyses show that fleas first evolved to feed on marsupials. Fleas were likely an obscure group during the dinosaur age.

Fleas came to prominence after the dinosaur extinction event, likely because of new emerging niches on fury mammals which survived the likely asteroid collision which caused a dust cloud and cooled the earth.

Elite athletes

The high jump is a flea’s favourite event. The larvae that feed on the dried blood subsequently form a cocoon with a new adult inside. The new flea won’t hatch immediately. It will wait and wait (for several months).

If you’ve seen the film Aliens, you may recall the scene in which the alien “eggs” are activated by the presence of the human heroes. That is exactly what fleas in their cocoons are waiting for as well. Dogs or even you walk around and flea emerges and unleashes its legs springing power to land on a new host.

Fleas can jump up to 25 cm high!

In heavily infested households, human victims have flea bites on their legs up to 25 cm from the ground - a telltale sign of infestation. Such a jump would mean that a human athlete would be jumping as high as 305 m over the Sydney Tower. The acceleration is comparable to a Space Shuttle launch.

Living better with fleas

In coastal Australia, the flea battle is on year-round. Will we ever be able to eliminate them all together? Unlikely!

Fleas are here to stay. Reducing their numbers is well-justified, not just because of the itchiness they cause to our pets. Fleas can carry some of their own little fleas or human diseases with them. Diseases such as Cat Flea Typhus (Rickettsia felis) and Cat Scratch Fever (Bartonella henselae) are transmitted by fleas.

Year round control with parasiticides (there are lots of good ones to choose from) with bit of environmental control (vacuuming) is the way to go. Don’t despair, talk to your vet. They are the experts in flea management.

This article is part of a series profiling our “hidden housemates”. Are you a researcher with an idea for a “hidden housemates” story? Get in touch.