Does it Fart: which animals fart, which don’t, and why

Here’s a mind-boggling fact: Almost all mammals fart, yet the sloth does not.

I learned this because I read Does it Fart? A Definitive Field Guide to Animal Flatulence, which published in April. It’s a small (133 pages), illustrated compendium of all things that toot from the rear.

Each page of the book is devoted to one animal and one question: Does it fart?

Orangutans? Yes.

Salamanders? Maybe.

Sloths? No.

Dani Rabaiotti, a PhD zoology student at the Zoological Society of London and co-author of the book, studies how climate change impacts African wild dogs. But in early 2017, her brother asked her, “Do snakes fart?” and she didn’t know the answer. So she posed it to an expert on Twitter. (Spoiler: They do.)

Virginia Tech ecologist Nick Caruso saw the tweet and was inspired to create the hashtag #DoesItFart. The tag became a forum for discussions on animals and whether they pass gas.

When writing Does it Fart, Caruso and Rabaiotti never actually met in person (Rabaiotti is based in the UK, Caruso in the US). But inspired by the conversations in #DoesItFart on Twitter, they penned this book together and added cheeky illustrations by Ethan Kocak (see a few examples below). “We just had a mutual interest in farts,” Caruso explains of why their collaboration worked.

(The book was so successful, that the trio is publishing a sequel called True or Poo?: The Definitive Field Guide to Filthy Animal Facts and Falsehoods. It comes out in the US on Tuesday, October 23. It’s already for sale in the UK.)

Overall, Caruso hopes Does it Fart will help readers appreciate how “there’s still a lot that we don’t know, whether it be about farts or a lot of other aspects about biology,” he says.

But also: What we do know about farts is surprisingly wondrous. Here are a few endearing lessons.

1) Farts take on many forms across the animal kingdom

Rhinos do fart. Fun!
Ethan Kocak

First off, “fart” is not a scientific term, so Caruso and Rabaiotti had to decide what counts as one.

They decided on a simple definition: Farts are simply gas that comes out of the end opposite the mouth, Rabaiotti says. That definition encompasses a wide range of biological processes.

For humans and our mammalian relatives, farts are mainly the result of digestion. Microbes break down food in our guts and produce gases like carbon dioxide or methane as a byproduct. In humans, these microbes help us break down fibrous plant materials found in beans, grains, and vegetables. Likewise, horses fart so much because their diet is mostly plant-based, and their fibrous food gets digested through fermentation in the back half of their digestive tract. (Elephants and rhinos do this too.) But diets full of meat can produce a lot of farts too (as red meat contains sulfur and other foul-smelling compounds). Seal farts, the authors relay, smell like fish.

But some species also swallow air and then expel it out their butts. That counts as a fart too.

Sonoran coral snakes have an anus-like hole called a cloaca that can suck in air and then expel it with a popping noise to ward off predators. Yup, that’s a fart.

Zebras fart when startled (we’ve all been there). Cows fart, and also burp around 100 to 200 kilograms of methane a year each, which is a big problem for global warming.

Octopuses don’t fart gas, but they can expel a jet of water to propel themselves through the ocean (the authors call this a “pseudo-fart”). Parrots don’t fart, but they potentially can mimic the sound of human butt toots. No one really knows if spiders fart; it’s just never been studied. And whale farts “have only been captured a handful of times on camera,” Caruso and Rabaiotti write.

The entry on sloths explains that while they eat a lot of plants, they avoid releasing gas through the quirk of their slow digestion. “They only poo about every three weeks,” says Rabaiotti.

If gases accumulated in sloths’ intestines over that long a time, they might get sick — and even burst. So would-be sloth farts are simply reabsorbed through the intestines into the bloodstream. The gases are then respired out of the lungs: literal fart breath.

There are some cases where researchers just don’t know if animals fart or not. Like with salamanders and other amphibians, which “may not possess strong-enough sphincter muscles to create the necessary pressure for a definitive flatus,” the authors write. Gases may ooze out of their bums continually. Is that a fart? Some questions in science are best left to philosophy.

I was also surprised to learn that bat farts have never been recorded in the scientific literature. And it’s possible they don’t exist: Bats digest their food within minutes of eating it. The food waste may be excreted so quickly that nary a single fart can be formed.

2) In many cases, farts help animals survive

If the bolson pupfish doesn’t fart, it dies!
Ethan Kocak

I took away from the book an appreciation of the many ways farts are used across the animal kingdom. Sure, many farts are merely the byproduct of digestion, are smelly, and serve no real purpose. But there’s a wide array of behaviors in which farts prove useful, adaptive even.

Herring — a small saltwater fish most commonly served pickled — use farts to communicate with one another, so that they can stay close in a shoal, even in the dark.

Manatees hold on to their farts to remain buoyant in the water, and they are known to fart before diving from the surface. Caruso says it’s easy to spot a constipated manatee: These will be swimming with their tails up out of the water, unable to expel the buoyant gas from their behinds.

One species of beaded lacewing (they kind of look like a cross between a moth and a dragonfly), when in the larval stage, have farts that contain a chemical that stuns termites. Then the lacewing eats the stunned, farted-upon termite. Yum.

For one species of pupfish, farting is a matter of life or death. These small freshwater fish feed on algae in the rivers of South America. These algae produce gas, which inflates the fish intestines and causes the fish to float to the surface, where they’re more vulnerable to being eaten. So they have to fart to sink back to safety. “Which I thought was hilarious,” Rabaiotti says. “Imagine them flopping them about on the surface, desperately trying to fart.” For me, that would be a singularly torturous version of hell.

The book doesn’t really note what all these farts smell like. Elephants, we learn, “produce incredibly pungent farts.” But are these more pungent than zebra farts? More malodorous than manatee butt belches? And what is the quality of their odor: musky, sulfury, briny? Reader, you may need to go out into the world and find out.

3) And finally, here’s a question I didn’t even know I wanted answered: Did dinosaurs fart?

If no one was around to hear dinosaur farts, did they even make a sound?
Ethan Kocak

Dinosaurs roamed and ruled the Earth for hundreds of millions of years. But did they stink up the place?

First, the evidence against: It’s believed that modern-day birds are the evolutionary descendants of dinosaurs. And generally speaking, birds don’t fart; they lack the stomach bacteria that builds up gas in their intestines.

“But then, dinosaurs were pretty diverse,” Rabaiotti says. There were meat eaters like the fearsome Tyrannosaurus, and there were giants like sauropods that ate only plants. It’s possible the vegetarian dinosaurs had the gut bacteria necessary to break down these fibrous plants and produce gas.

“Those animals probably did fart,” Rabaiotti says, “and we’re pretty certain that they don’t fart anymore.”

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