The many interactions we have with other species—and their microbes—make us who we are, whether that be man, woman…or werewolf. That’s right, if monsters existed, they’d have microbiomes, too.

By imagining the types of bacteria that would live on ghouls such as vampires, mummies, zombies, and werewolves, we hit on a few insights into real-life microbial relationships. Read along to find out more.

1. Our bodies are engineers.
Similar to how termites build grand mounds in which to live, our own bodies engineer the ecosystems where microbes reside. On each part of our body, specialized glands and compounds favor some bacteria and disfavor others. Your apocrine glands in your armpits, for example, serve no role other than to feed beneficial bacteria (the ones that produce your armpit odors but that also provide other, less ambiguous services, such as defending you from pathogens).

Now, let’s consider the microbes of a werewolf. Because the glands of wolves and humans are different, they engineer bodily ecosystems that contain different microbes. Therefore, when a man transforms into a werewolf, the ecosystem of his skin likely shifts as the composition of glands and habitat shifts. Armpit glands disappear, and anal glands become more prominent. Naked skin covered in Staphylococcus gives way to fur and species of Pseudomonas, and with it all the unmistakable odor of werewolf, something I imagine to be wet dog with a hint of man.

2. Strange diets favor strange gut microbes.
We know that human diets influence which gut microbes we have (the reverse may also true to some extent—that is, the microbes you have may influence which diet you seek). Some of these changes are short-term. For instance, what you ate last week might have favored some microbes relative to others. But bigger changes are those associated with the ancient differences among groups of organisms. For example, we know that blood-feeding animals tend to acquire, and host, very unique microbes. Indeed, their guts tend to have fewer kinds of microbes and to be dominated by unusual microbes found in few other places. For example, Aeromonas bacteria are found in the guts of vampire bats, mosquitoes, and leeches, where they appear to aid in the digestion of blood. Aeromonas would likely dwell in the guts of vampires, too.

But what’s interesting about this microbe is that we don’t know how it colonized the guts of so many different blood feeders in the first place. Perhaps it’s more common than we know in the environment and colonizes any animal that begins to feed on blood. Perhaps it’s an ancient associate passed down mother bat to baby bat, mother leech to baby leech. Or maybe it’s a microbe found in mammal blood—a microbe in you right now—that hasn’t yet been noticed or studied. We just don’t know.

3. Nocturnal animals rely on odors; most odors are microbial.
Species active during the day, such as humans, rely on vision relatively more than other senses. (There are interesting exceptions, such as vultures, which can pick up a whiff of death miles away.) On the other hand, nocturnal species listen and, to an even greater extent, smell their world. As a result, when nocturnal species want to get sexy, they often employ odors.

Nearly all odors produced by mammal bodies are produced by microbes (including those that attract or repel mosquitoes at close distances!). When dogs sniff each other, they’re sniffing each others’ microbes, for example. To produce interesting odors, nocturnal mammals have evolved a rich array of special love-stink glands. Bats in particular release many different aromas, depending on their mood or intent. Not all bat odors are attractive to humans (and bat-pollinated flowers tend to smell a little funky).

Vampires, in as much as they are nocturnal, are likely to also have enlarged glands that feed microbes that in turn produce odors. What would vampires smell like? I suppose it would depend upon their intent.

4. Our bodies expend great energy to control their microbes, but they stop doing so in death.
Every breath of air you take has more than a thousand species of bacteria, fungi, and other microscopic life forms in it. Some can kill you. Some you depend upon for existence. Most don’t have names. Yet, your actual body hosts far fewer kinds of life. It is diverse, containing hundreds of species, and yet it’s far, far less diverse than a pinch of soil. Indeed, most of the bacterial lineages on earth are found in the soil of Central Park!

The difference between the diversity of your body and that of soil pinch is a measure of the hard work your body does to control which microbes live on it. Conversely, when you die (or even as you start to age), that control weakens. Zombies appear to have no immune systems, and thus no ability to control which microbes live on or in them. As a result, their bodies quickly come to resemble the soil in its diversity as microbes find and consume the nutrients in skin cells, break into organs, and otherwise cause havoc. A pinch of zombie skin, in other words, is likely to contain thousands rather than mere hundreds of species—a kind of microbial wonderland.

5. Most of the microbes in our foods come from our bodies.
The microbes in cheese, sourdough bread, and yogurt made from scratch all come from the bodies of mammals of one sort or another. Depending on the food, the sources are skin microbes, vaginal microbes, or even oral microbes; you eat what you are. One of the most common commercial sourdough starters, for instance, uses bacteria that originally came from the feces of rats. This might seem gross, but there has been interplay between our bodies and our food since the origin of agriculture and the need to store food, if not longer.

What is gross, though, is any food descended from a zombie. Such food would likely contain unusual microbes—microbes from the body of the zombie or even from the insects tunneling in and out of its flesh as it walks, such insects carrying bacteria able to turn foods sour or even dangerous rather than lovely. If you find yourself at a zombie cocktail party, avoid the cheese.

6. Storing food depends on controlling which microbes grow.
One of the greatest innovations in human history is the ability to store food, which we do by controlling its microbes. Wines, beers, salted fish, and even caviar all rely on our ability to favor microbes that we like relative to those that turn our foods and drinks to rot.

Mummies were stored in similar ways—by favoring some bacteria relative to others, and specifically those bacteria that helped to preserve the body. As a result, we can predict that monster mummies, like real ones (or like wine or cheese) would have relatively few kinds of microbes—ones tolerant of dry, salty, conditions. But this would change quickly. Get a mummy wet, and it will start to rot—almost immediately—as has begun to happen to the very real mummies buried in the Chilean desert and recently exposed to increasing levels of dew.

Learn more…
For more on our many daily interactions with other species, including microbes, see The Wild Life of Our Bodies. In it, author Rob Dunn considers how those interactions shape, and fundamentally change, us. This transition is not from wild to civilized, but instead from one type of “wild” to another, since the one absolutely unambiguous thing we have discovered about ourselves is that we are always covered with, and connected to, other species.