38: Fleas

I write to you from Arapahoe, Ute, and Cheyenne land. I am interested in learning about the different animals that live in the place where I was born. I want to mention that biological classification as taught by western science has its roots in racism, sexism, and transphobia – here’s a good explainer about why.

Did you know that Colorado has over 80 species of flea, the most of nearly any state? We are going to talk about all of them here because I really do not think I could write 80 newsletters about fleas.

Obviously the first thing you thought of when you heard fleas was, plague! It is 2020, after all. Most of those flea species are not susceptible to Yersinia pestis, the bacteria that causes bubonic plague, but a few of them are – notably the rock squirrel flea (Oropsylla montanus), who lives on, unsurprisingly, rock squirrels, but also on prairie dogs, wood rats, and other rodents that make burrows or stick nests. The fleas eat the bacteria, which then forms a plug inside their digestive systems that slowly kill the fleas. I really do mean slowly – it averages 53 days for flea to be capable of transmitting the bacteria, giving you an idea of just how long it can live inside the flea’s body. Meanwhile, the flea slowly starves, becoming more and more desperate to bite potential food sources. These are generally mammals in the area. A recently discovered common plague vector for humans is cats – yet another reason to keep kitty indoors, especially in Colorado, where plague is endemic.

So that was a lot about a disease that impacts fleas, but what about fleas themselves? They are small insects with a flattened profile (easier to slip through hair or feathers), wingless in adulthood, that feed on blood. They have long hind limbs designed for jumping onto their prey and have specialized mouths for sucking blood. Despite having so many flea species here, Colorado is actually not very conducive to the flea lifestyle – it is too dry. As a result, the larval stage lasts several months, whereas in a more humid environment, it can occur more quickly. This is why they like those rodent burrows – humidity can be significantly higher within them.

Fleas in general are part of the order Siphonaptera, from the Greek siphon, meaning pipe or tube for drawing wine from a cask. Indeed, animal blood is the wine of the flea world, and Siphonaptera evolved sometime in the Cretaceous, first feasting on our small mammalian ancestors in the period before branching out to other types of animals, including birds.

I do not recommend the images on the Wikipedia page about fleas, particularly the one of the human foot experiencing an infestation. You have been warned.