Well, hey there friends. Do you want to hear a story?

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Once upon a time there was a bunny, and she was a good little bunny, and she hopped around her neighborhood every day, finding food that she liked to eat and drinking out of rushing streams and pooping in the bushes, and at night she and her family slept in a hole under a big tree, and every so often one of her friends, a brother or somebody, would get gobbled up by a bigger animal, a jaguar or something. But you know that was cool because they're bunnies and, when you are a bunny, you get used to the idea that some day you're probably going to get snacked on.

So one day Bunny and a couple of her friends were scurrying around the meadow when they accidentally hopped right up the ramp of a spaceship that was headed to Planet Wonderful. The bunnies didn't know that they'd done that, of course, and when the doors closed behind the bunnies and the spaceship blasted off, they were totally freaked out. But eventually, the doors opened again and they hopped down the ramp at the loveliest meadow they had ever seen. Planet Wonderful was just perfect for Bunny and her friends. There were fields of four-leaf clover and little vegetable patches tended by tall spindly carrot people; big dumb cabbages rolled around in the meadows and mooed at the bunnies when they hopped up to nibble on them. Bunny and her associates didn't even have to find a tree or a hole to sleep in because there was nothing on Planet Wonderful that wanted to eat them. It was so dreamy.

Pretty soon Bunny became romantically involved with one of her friends and they started having baby bunnies, and some of the other bunnies had baby bunnies too. And those babies were big and strong and healthy and just as voracious for cabbages and carrot people as Bunny herself had been when she'd arrived. Pretty soon Planet Wonderful was covered in bunnies. In fact there were so many bunnies that the cabbage cows and carrot people feared them and their numbers began to dwindle. And the bunnies lived happily ever after until they'd eaten every single carrot, cabbage cow and four-leaf clover on the planet. What happened after that is a story for, well, I'm going to tell you that in just a minute.

So the end of that story is actually the beginning of this video- about exotic invasive species. They had evolved in a special little environment where they had a very specific place or purpose, and somehow, probably with the help of us humans, they got to a completely different ecosystem. In some cases these animals can't handle the new ecosystem and they die, and in other cases they just, you know, chug along and make life work like everybody else. But in some cases, like in the case of Bunny on Planet Wonderful, they show up in their new ecosystem and they go all hegemonic on it. They might become super predators or they might out compete other species that are living in that ecosystem. Sometimes they manage to completely alter the habitat of the place that they invade. Sometimes they hybridize with species that are already living in that environment, diluting their gene pool to the point of extinction. And sometimes along with their... selves they'll bring in a new disease that will completely wipe out the local population. But you know they're really happy to be there because this is now, they've come upon this wonderful bountiful paradise. A paradise for them, but for everyone else, a hell.

To illustrate what I'm taking about, I actually with me today in the studio a couple of more pernicious but still very adorable examples -- um, you can maybe hear him in the background already, uh -- of invasive species in the United States.

So this little girl is an European starling. They were introduced to America because there was a rich guy in New York who just couldn't live with the fact that there were animals mentioned in Shakespeare that didn't live in America and so he decided to release 60 starlings into New York City's Central Park. And now there are 200 million of them in the United States. Yeah, you did a pretty good job. You really like it here. They are very gregarious, they love living in large flocks, and they have been out competing native birds in America for space and for food and for general peace and quiet since around 1890.

This is the red-tailed boa, which is what you call a boa constrictor, generally. They're beautiful and sort of lovely to have around if you're a certain type of person, which is why they were brought to America as pets. Maybe a few people were like, "maybe I don't want this thing around my six-month-old infant, it's getting kind of big," and, uh, so they just let them go into the Everglades and now they are very happy to be in the Everglades and have become an invasive species there. We're gonna kiss. Me and Daisy are gonna kiss.

To illustrate what one of these exotic invasives can do to an ecosystem, lets look at kudzu, the vine that ate the American Southeast. Kudzu was brought to American from Japan because it was a cute little ornamental vine with purple flowers and it smelled like Laffy Taffy. After a while, because it grew so well, people started having weird ideas about using it to stabilize hillsides or to feed to livestock. And kudzu appreciated all of the assistance it was getting, being distributed across the Southeast, but... but let me tell you, it didn't actually need the help. Maybe it was the soil, maybe it was the hot, humid climate, I don't know; but whatever it was, kudzu took it and made a lot of the Southeast look like this. You can't blame the plant; it's not kudzu's fault that it takes over trees and entire landscapes and cars that happen to be parked in the same place for too long. Kudzu, like thousands of other plants, were just planted because people thought that it looked good, and it happened to be the one that was trouble.

So Kudzu was a big oops moment in the course of American natural history, but compared with a lot of other invasive species, kudzu looks, you know, like a bunch of overgrown bushes in some old lady's yard. Take the brown tree snake, for example, a mildly venomous but very aggressive snake that was introduced Guam during World War II and pretty much collapsed the entire ecosystem of the island. Before World War II Guam didn't have any snakes except the Brahminy blind snake which is tiny and blind and basically looks and acts like an earthworm. No offense to any Brahminy blind snakes that are watching this- ha! You're not watching it 'cause you're blind. But during World War II the brown tree snake hitched a ride on a military cargo ship from the South Pacific and showed up in Guam, and seriously -- Guam was the brown tree snake's Planet Wonderful. They just started eating and never stopped.

They had no predators and no competitors and, as a result, since the snakes' arrival, 10 of the 11 native bird species in Guam have gone extinct. Small mammals on the island are increasingly rare and, since birds were major pollinators of the plants, the plant ecosystems are also crashing. So it's a complete frickin' fiasco and, on top of that, there are now, on Guam, 13000 snakes per square mile. 13000 mildly venomous snakes per square mile! In addition to that being completely, like... bluuuuh, the snakes are also always climbing up power lines and getting electrocuted and causing power outages, and they generally make living on Guam or visiting Guam kind of a terrifying experience.

Here's the question though: what do you do when a bunch of snakes or the equivalent of Audrey II from "The Little Shop of Horrors" starts to invade your little island? Well, that is the question that people have been trying to answer for decades without as much, uh, success as one might like. Once something like kudzu or the brown tree snake is loose, it's pretty much impossible to round them all up, so the first line of defense has to be to prevent the things from coming in the first place. These days that doesn't actually work very well because people are very mobile, we like to move around, and when we move around we like to bring our pet Burmese python with us. But because we've seen this happen so many times before all over the globe, it's becoming easier to spot an alien invasion while it's happening and nip it in the bud before it goes all "Brown Tree Snake Code Red." A lot of times we actually had to do this the old-fashioned way, going in and actually, uh, killing every invading animal. In Florida, where I grew up, they actually encouraged people to go hunting for feral pigs. Uh, I don't think they went as far as to put a bounty on their heads, but they did put together some some mighty good cookbooks for how to make delicious feral pig stews.

But another trick that we've been using is actually bringing in another species from outside the ecosystem to combat the current invader. This is called biological control and as you might imagine it's had some successes. It's has some pretty tremendous failures -- for example, the lady who swallowed the spider to catch the fly. There are plenty of examples of when biological control has actually worked and, nowadays we are actually developing like a fungus or a disease that will go after a specific organism and kill it. But probably the best example of biological control going awry is when they brought mongoose into Hawaii to fight, uh, the invasive rats, but it turned out that mongoose actually much preferred eating the eggs of native bird species to having to go chase down rats. I don't know who didn't see this coming. I mean when you are given the choice between eating the raw flesh of a rat or an egg, I think most species would go for the egg. But gosh darn it if now there aren't a lot of mongoose on Hawaii and a lot fewer native birds! 

So I know that we are really hating on invasive species right now but there are actually some examples of where species invasion has taken an unexpectedly heroic turn. Take, for example, the Asian clam, which, showed up in Washington state around the 1930s, brought in by Chinese immigrants who thought that they were super yummy. So, of course, as you might imagine, the clams didn't stay in people's lunchboxes. Pretty soon they were in rivers and streams all over the country, partially because they just don't care much about anything. They can live pretty much anywhere and, if they can't find another clam to breed with, they're hermaphroditic, so they can just fertilize themselves. And on top of that, when conditions are perfect, they can make about 350 babies per day. Talk about business time. And they'll live anywhere -- lakes, rivers, streams, a glass of orange juice -- they just don't care.

On the other side of the bivalve pickiness spectrum, there are, or, at least, used to be, tons of native species of American clams, and they actually do care quite a bit about their water quality and where they live and whether or not they have another mussel near by to mate with. For starters, most of them need clean gravel to live on, but the reproductive strategies and habits are unbelievably fancy and fussy. A lot of them require a specific species of host fish for their larva to attach to and grow on. And of course there are some species that prefer to have, uh, Barry White playing, and could you please turn down the thermostat a little bit and turn on the humidifier? I think that would help me get into the mood. And, in particular, freshwater mussels aren't actually doing that well these days because, mostly, of pressures from people. Always with the people! But, like I said before, the Asian freshwater clams are pretty much down for anything, and that actually turns out to be pretty good because the native freshwater mussels... are kinda going extinct.

And that's actually been a good thing for the ecosystems that they've been introduced to, because there's birds and fish and raccoons and crayfish and all these animals that rely on freshwater mussels to be there, and the picky native ones, they're getting really rare, but you don't want the whole ecosystem to have to collapse because of that. So that's pretty much the exception to the rule. Invasive species: almost always very bad, but also very interesting. And now I'm going to show you a picture of an exotic Burmese python messing with a native Florida alligator.

Good night and good luck. If you have questions or suggestions for other things that we should cover on SciShow you can see us on Twitter an Facebook and of course down below in the YouTube comments. We will always be there, uh, because we love to see you. Goodbye.

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