Flatworms fence with their penises and other gross science facts

Flatworms fence with their penises and other gross science facts

October 21, 2018 0 By Nazmul Khan


It sounds like something out of a filthy fairy tale: the mountain tree shrew visits certain species of pitcher plant to grab a bite of nectar, and poop into the plant’s commode-shaped cup. These plants appear to have evolved so that their openings fit perfectly under the tree shrew’s behind, and they’re sturdy enough to support the animal’s weight.

It’s a crappy relationship, in the sense that the pitcher plant is actually crapped on — but the pitcher plant gets nutrients out of the deal by extracting them from the shrew’s feces. “Everything that led up to that is amazing,” says Ethan Kocak, illustrator of the new book True or Poo? The Definitive Field Guide to Filthy Animal Facts and Falsehoods. The book, which hits shelves in the US on October 23rd, explores the stories people tell about animals — pronouncing the facts true, and the lies poo. The pitcher plant toilet is, delightfully, true.

The book’s authors, zoology graduate student Dani Rabaiotti and postdoctoral scientist Nick Caruso, are the same team that brought us the best-selling guide to animal flatulence, Does it Fart?. But True or Poo? covers a larger range of subjects, from the fact that flatworms fight each other with their genitalia (true) to the myth that camels store water in their humps (poo). The team disagrees somewhat about what the book is really about. Rabaiotti says it covers poop and gross animal habits. But Kocak, the illustrator, says it’s actually a quest for truth.


The mountain tree shrew, Tupaia montana, pooping into its pitcher plant.
Illustration by Ethan Kocak/True or Poo?

Ultimately, the team’s goal is to debunk some of the more pervasive myths surrounding animals — like that if you cut an earthworm in half, you get two earthworms. (You don’t. You just get a sliced up earthworm.) They set out to find the origins of these fictions, and supplant them with incredible facts. “You don’t need to make stuff up about them,” Rabaiotti says. “They do enough weird stuff already.”

Rabaiotti works in the UK, and Caruso and Kocak are both in the US — so even though this is the team’s second book together, they still have never met each other in person. For this book, too, they leaned heavily on tools like email and Google Docs that let them work together remotely. Caruso says his inbox still hasn’t recovered after the deluge of fart emails from last year. “Now it’s all poo and penises,” he says. “So that’s pretty great.”

The Verge spoke with Rabaiotti, Caruso, and Kocak about elephants eating poo, anus-adjacent glands, and why electric eels are liars.

This interview has been edited for clarity and brevity.

Were there any animal facts that were almost too gross to include?

Dani Rabaiotti: There was one thing in particular that there was a disagreement about leaving in between the US and UK publishers, because our UK publisher found it so gross: that baby elephants reach into their mother’s butt and eat their poo in order to get the right bacteria in their digestive systems. Our publisher just highlighted and just went, “Too Gross?”

Ethan Kocak: I didn’t think I was going to get away with the penis fencing illustration. It’s two flatworms but they battle each other with penises, and I drew them as literally fencing, with the masks and everything. I did not think that was going to make it, but it did.


Hermaphroditic flatworms can make both eggs and sperm. They fight each other with their extendable, pointy penises, and the loser of the fight gets squirted full of sperm.
Illustration by Ethan Kocak/True or Poo?

Can we talk about beaver butts? Because I keep hearing that vanilla-scented secretions from beaver butts are flavoring my food — but your book tells me that’s mostly not true?

Nick Caruso: Yes, there’s a certain amount of fear mongering, because it’s like, “Oh this substance is produced pretty close to the beaver’s butt — I’d describe it as anus-adjacent — and it’s in your food.” Even if it is, it’s perfectly safe: just because it’s near the butt, doesn’t mean that it’s poop. But also it’s just really expensive. You think about producing something where you actually have to milk it from an animal to get excretions versus producing it artificially. It’s way easier to not go around taking beavers and milking their, their uh —

Rabaiotti: — butts!

Why debunk animal myths? What’s the harm in believing that there are beaver butt gland secretions in my vanilla ice cream?

Kocak: In the climate of fake news and all that, I think it’s more important to be truthful and not allow even “harmless” myths. That might not be very funny, but that’s how I feel about it.

Rabaiotti: Even some of the more harmless-sounding ones can change the way a person treats an animal and have a negative impact. For example, a lot of people believe if you cut an earthworm in half you get two earthworms. If a kid believes that, they might go around cutting loads of earthworms in half. And that’s not cool because then you’ve just damaged that animal for no reason.

What turned out to be poo, that going into this you thought was definitely going to be true?

Rabaiotti: That vulture poo is disinfectant, and that they poo on their legs to kill bacteria. But actually when I read into it and spoke to vets and vulture experts, they were like, “Oh my god no, vulture poo is really just full of horrible bacteria. Do not touch that stuff.” That was kind of a shocker to me.

Kocak: I should stop rubbing that in my wounds…

Caruso: I should have known, but in Jurassic Park, where the T. rex can’t see you if you stand still. I guess I never really thought about it too much, but I was like, “Why would they lie to me about this?” But it’s not true, they can definitely see you — and even if they couldn’t, they could smell you!

What’s your favorite thing that you learned?

Kocak: The parrot fish pooping sand. The premise being that bumphead parrotfish eat coral, and digest it, and poop out white sand, and therefore that’s where white sand beaches come from.

Rabaiotti: And it’s true. Not all white sand beaches — it’s particularly the Maldives. It must be so uncomfortable being a bumphead parrotfish. I’m glad I don’t have to poo sand.

Kocak: I love the thought of people paying extra money to go lay on fish shit.

Rabaiotti: For me, the most surprising one was that platypuses don’t have stomachs. That was one where I was like, “Nooo, that can’t be true!” And then it was totally true. They eat their food and then it just goes straight through into the intestines without there being a pouch that produces acid. Weirdos.


The bumphead parrotfish poops sand (true).
Illustration by Ethan Kocak/True or Poo?

Were there any myths that stumped you, and took some investigating?

Rabaiotti: The one about how you’re always within six feet of a rat. That was one where it was like, “Ooh, not sure.”

Caruso: So that myth started in the early 1900s when W.R. Boelter surveyed people in the countryside about how many rats they see. He was writing a book about rats being a problem. And so then he estimated based on this small survey how many rats there are in the entire country. And from there it was like, “Oh [the number of] rats are equal to people in all of England.” It took some pretty big assumptions that were clearly not correct to get at those numbers.

Rabaiotti: One I found very tricky to verify was black widow females eating their mates, because so many species of spider share the same name. In the US apparently, the species that people refer to as a black widow doesn’t eat its mate, and a lot of the spiders in the widow family don’t eat their mate, or at least do so very rarely. But then the Australian widow does actually eat its mate quite a lot of the time. So that was quite a tricky one to get to the bottom of. So we went with it’s sort of a myth in terms of not all black widows eat their mates. But some do.

A bunch of these — like that salamanders are born from fire, or ostriches bury their heads in the sand, or earwigs lay eggs in ears — come from a Roman naturalist you write “was very wrong about a lot of things,” right?

Rabaiotti: Three words: Pliny the Elder. He made up so many of these myths. Every time you’re like, “Oh I wonder where this myth came from?” It’s like, “And then Pliny the Elder made it up.” Basically he just wrote this really big book about the natural kingdom, but that was back in the day when they almost looked for morals in animal behavior. He kind of melded the animal behavior to maybe suit his agenda at the time, which meant that not all of it was entirely accurate. Classic Pliny.

Caruso: We were cursing Pliny while writing this. Shaking our fists at the sky.

Are there any that you’re just devastated to find out are false?

Kocak: Electric eels not being eels. I’m crushed. That’s a nice fish.

Caruso: Didn’t you draw it saying “liar” in electricity?

Kocak: I did.

Rabaiotti: That’s how crushed Ethan was.

Was there anything that you learned from publishing Does it Fart? that changed how you approached this book?

Kocak: Don’t yell “butthole” in an interview.

Rabaiotti: I obviously didn’t learn that…





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