Thanks to Brilliant for supporting this SciShow List Show!

Because you watch SciShow, Brilliant is offering you a  30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. You can bust your butt, you can put your butt on the line, you can sit on your butt, and if you’re a certain sort of person, sometimes the sun will even shine out of your butt.

But most people don’t lose their butts. If they did, well, that would be very unfortunate. But other animals can and  sometimes do lose their butts, and that isn’t even always a bad thing.

So hold onto your seat, and let’s get into it! [ INTRO ] Imagine not pooping for eight months. Because you lost your butt. We’re all familiar with animals like lizards that can choose to remove their tails to avoid predation.

This is called autotomy. But Ananteris scorpions  can lose their entire butts along with their tails. Scorpions of both sexes will  drop the ends of their tails, which includes their all-important anus, when grabbed by a predator.

Without a butt, it can be challenging or —let’s be real — impossible to do your business, so to speak. And so, possibly to distract them from the building pressure to go, these guys just have lots of sex instead! Tail-less and anus-less scorpions will continue to mate until constipation eventually kills them, around 8 months later.

And tail loss doesn’t seem to affect the mating success of the males, so I guess scorpion ladies aren’t all that concerned about a lack of junk in a male’s trunk. Females can also still reproduce without a tail, though tailless females do  produce fewer offspring. Researchers aren’t sure if that’s because the extra poop leaves less room for babies, or if it’s because of a buildup of toxins.

Who really cares which one? They’re both awful. When researchers were investigating butt loss in Anateris scorpions, females were less likely to drop their tails than males were, which they argue is explained by that decrease in reproductive success.

Incidentally, the most recent research seeking to answer these important questions won a 2022 Ig Nobel Prize. If you’re unfamiliar, those awards are a semi-satirical way to acknowledge research projects that are a bit on the silly side. Hopefully, it inspires more scientists to do butt-centric research, because what could be more interesting?

But those scorpions aren't the only creatures that lose their butts. Meet Pycnogonum litorale. It's basically an Alien face-hugger that lives in the sea.

Think about that the next time you're out for a nice swim in the ocean. You're welcome. These animals are found in the Atlantic Ocean, the North Sea, the English Channel, and the Mediterranean Sea.

Fortunately, sea spiders target sea anemones, not people. And they do mostly feed at night. Mostly.

In January of 2023, researchers reported that the juvenile sea spiders can lose their butts and still be okay. They were testing the regenerative abilities of the sea spiders. For a while, researchers thought that animals that molt couldn’t regrow a  part of their primary body axis, which includes all the main stuff from the back to belly and head to butt.

Unlike the Anateris scorpion, sea spider butts —including the anus— will grow back. In the meantime, they can just vomit up their poop whenever they feel the urge to “go.” Which is handy. To figure all this out, the researchers took 23 juvenile specimens that were at least instar stage V, which means they were old enough to have an anus.

Then they cut off their butts. All the specimens survived that procedure, though two of them died a couple weeks later. Weirdly enough, one of them actually vanished after molting.

Like, vanished. Hopefully, the researchers checked the ventilation system and ceiling panels before shrugging this off because, ugh. The research was an improvement over older research where the sea spiders were subjected to butt removal and also starved.

Personally, I don't think it should  have been surprising to see that one-two combo result in death. This newer research showed that molting juvenile sea spiders can regrow lost butts and lost legs, too. Though they don’t always seem to regrow the lost parts quite perfectly.

Some may not regrow all of their missing legs, for example. It’s possible that ancestral marine arthropods could have also done this, since sea spiders diverged faster than the rest of their subphylum, which also includes horseshoe crabs and arachnids. Interestingly, this strange but important research might say something about the evolution of the anus.

Because vomiting up your poop isn’t actually a unique  skill in the animal kingdom. Other animals do it because they don’t have anuses, ever. So maybe this butt-stealing research was worth it, after all.

Speaking of weird sea creatures … the warty comb jelly Mnemiopsis leidyi apparently only has an anus when it needs to poop. The researcher who discovered this disappearing anus was looking at some larval warty comb jellies with a microscope and noticed that some of them were missing that all-important structure. Although there could be another explanation for this.

Others have argued that the anal pore just shrinks when it isn’t needed, and is just too small for a microscope to see. And because research about disappearing anuses tends to beget other research about disappearing anuses, the same scientist did a follow-up study with two other comb jelly species. But he didn’t observe anything like this in either of them.

So it’s probably safe to say that more research needs to happen before we’ll really understand the disappearing anus thing. That seems worthy of university funding. Annelid worms have special butts that contain … wait for it … eyes.

And a brain. These special butts are grown and shed as a part of the worm’s reproductive cycle. Apparently, there’s no limit to the many unique and wonderful ways animals can get busy.

Several annelid worm groups, including Megasyllis and Ramisyllis, engage in a reproductive technique called schizogamy. This means they basically split themselves apart, and their back ends turn into self-powered sex machines called stolons. These little stolons can be either male or female , and they develop eyes, specialized swimming structures, and a sort of pseudo-brain.

And, of course, everything they need to make new worms. When they’re ready, the worms shed their back ends so they can swim around looking for and mating with other stolons. So those guys are out there having all the fun while the rest of the worm has to hang around at home growing  its brand-new back end.

And the Japanese green syllid will actually go on to do this more than once. It's probably not lost on you how weird it is to grow an extra body part that not only has reproductive parts, but also eyes and a brain. In 2023, researchers found out how this is even possible.

Evidently, Japanese green syllid worms are able to express the genes that control head-formation in the middle of the worm's body, especially while the worms are developing their gonads. So the stolons develop a head and uniform-sized body segments, but not a true digestive system, since they don't really need that while they're out there looking for that special some-worm. Anything for love, I guess.

You might not have heard of annelid worms or warty comb jellies, but you’ve almost certainly heard of cicadas. Or at least, you’ve heard them, since their noisy summer screams are hard to miss. The only purpose an adult cicada has is to make new cicadas and annoy people, and it doesn’t have very much time to do it.

Which makes the existence of a certain fungus rather unfair. Massospora cicadina infects the periodical cicada broods — these are the ones that spend either 13 or 17 years underground. The fungus infects the insects as they emerge from the ground.

Imagine the Cordyceps from The Last of Us, except instead of biting other cicadas, the infected animals just have crazy mindless sex. And Pedro Pascal is conspicuously absent. First, the fungus causes the cicada's butt and genitals to fall off, which are replaced by a  white mass of fungal spores.

When the insects attempt to mate with each other, they pass the spores along, continuing this gnarly cycle. Like other types of zombie-making fungi, the infection also changes the insect’s behavior. Infected males will trick uninfected males into trying to mate with them by moving their wings in a similar way to receptive females.

And though humans would certainly not continue to walk the world without their butts, the cicadas sure do. Because in the grand scheme of things, when you only have a few weeks left to live, who really needs a butt, anyway? You may wonder what compels the poor cicadas to keep trying to get it on despite the conspicuous absence of reproductive parts.

Well, the answer may be that the fungus is feeding the cicadas psychoactive drugs! And it’s the good stuff, because they’re apparently strong enough to make the cicadas stop caring about the loss of their butt and genitals. In one study, researchers identified a type of amphetamine in fungal plugs from cicadas infected by Massospora cicadina.

In samples from a related fungus that infects yearly cicadas, the researchers found a type of psilocybin previously only known to exist in certain mushrooms. So these guys are probably too high to care, which is for the best, all things considered. From reproduction to predator avoidance to fungal infection, losing your butt does not sound like a fun experience.

But this research at least helps us understand that no matter how weird we think our world is, science can always find things that exceed our expectations. It also makes me grateful that humans are not among the many animals that can experience butt loss. I don’t know about you, but I’ve grown kind of attached to mine.

You might not have predicted that you’d learn about the odds of losing your butt today. But that just means you need to update your predictions. And Brilliant has a course to help you do that.

It’s called Introduction to Probability. See, Brilliant is an interactive online learning platform with thousands of lessons in science, computer science, and math. And fun statistics questions are kind of their wheelhouse.

After 16 lessons, you’ll have run simulations, learned some new rules, and generally gained all sorts  of probability knowledge. Or at least you’re likely to. You know, because …probability.

And if you didn’t get that joke, you need this course even more. You can find it at Brilliant.org/SciShow or the link in the description down below. That link also gives you 20% off an annual premium Brilliant subscription.

And you’ll get your first 30 days for free! Thanks for watching this SciShow List Show and thanks to Brilliant for supporting it! [ OUTRO ]