Fleas (Order Siphonaptera) are a relatively small group of insects; only about 2,200 species are known in the world. Some species have significant influence on animal and human health as they are key vectors of some disease. Studies on flea species and distribution are important because of these veterinary and human health connections. Still, we know little about some flea species’ host interactions and their larval stages.

Fleas are flightless insects (Class Insecta). They live as external parasites of mammals and birds, feeding on blood. As adults, most species are very small (but still visible to the eye); they are usually brown and narrow, an adaptation that allows them to hide and navigate in their hosts’ hair or feathers. Other adaptations include very strong claws to prevent easy dislodgement, mouth parts made for piercing skin, and legs for jumping hence escaping danger or finding a new home. They can jump notoriously far for their size.

The number of eggs produced varies by species but can be from a few to hundreds. Flea eggs are mostly found in the hosts nest or borrow (or bed). The larvae look like little worms: no limbs with a mouth adapted to feed on flea egg debris, and on bits of their host’s shedding skin.

Many flea species prefer, or are better adapted, to feed on only one or a few host species, but they survive on others if needed. The common names of fleas offer some idea of their favourite host, but it does not mean they are strictly host-specific parasites. In general, the smaller the favourite host species is, the less specific the flea.

Hosts with low immune systems will have more fleas. So, if you see wildlife that is flea infested, some other condition like starvation could be at play.

Fleas are vectors for some viral, bacterial, and parasitic diseases. For example, in the NWT, small mammals (voles and mice) were found to carry a bacterium called Bartonella sp., which can cause “cat-scratch” disease in humans if acquired.

Fleas are part of our ecosystems and have been around since the Jurassic. They may even have played a role in human’s evolution to a somewhat bald, less flea-infested body.

There are 32 species of fleas confirmed present in the NWT. Knowing what species of fleas are in the NWT helps our understanding of the complex host-human-ecosystem pathological interactions. If you find fleas, please report them.