There are plenty of horror  stories about invasive species.

Like wild hogs tearing up crops or zebra  mussels damaging lakeshore infrastructure. But every once in a while, invasive species  have actually been known to do some good.

Invasive species, or alien taxa, are critters  that thrive in places they didn’t originate in. They can disrupt a habitat’s natural balance  by displacing or outcompeting native species. And in the United States alone, these disruptions  cost roughly 21 billion dollars a year.

So it might seem like these species are  always pests that we’d like to eliminate. But as it turns out, some of them are  more beneficial than we initially thought. Like these seven invasive species  that have actually kinda helped. [♪ INTRO] Green anoles are quick little lizards  that you can find all over Florida.

They’re native there, but these days, you’re  more likely to spot their cousins, brown anoles. Brown anoles came from places like Cuba,   the Bahamas, and the Cayman Islands,  and they’re invasive in Florida. While they aren’t super destructive,  they do compete with the green guys.

Wherever brown anoles move in, the  green anole population gets pushed out. Despite this concern, brown anoles  have been pretty helpful to us. Because it turns out that local  mosquitoes have a taste for them.

And when mosquitoes are busy feasting on  lizards, that means they’re not bugging   residents, tourists, and other species  affected by mosquito-borne viruses. As an Florida man myself, I  definitely find this helpful. But lately, there’s another bully on the  playground that’s been causing a ruckus.

It’s a burlier, more aggressive, and equally  invasive lizard called the Peter’s rock agama,   and they’re starting to outcompete brown anoles. You might not immediately notice the difference  if the Peter’s rock agama replaced brown anoles. But mosquitoes don’t bite the  Peter’s rock agama as often.

So with fewer brown anoles to snack on, mosquitoes  will have to move back to other victims. We don’t yet know how this invasive lizard   showdown will affect the spread  of diseases like West Nile virus. The research is still ongoing, so we  still can’t quite determine whether   brown anoles are a net positive  to the overall Florida ecosystem.

But this next invader does  seem to be certifiably useful… In this case, it’s a grass that had an  unexpected benefit for the Botteri’s   sparrow, an unassuming little brown bird that has  historically lived in southern Texas and Arizona. But for a period in the late 1800s, the  Botteri’s sparrow was driven out of Arizona. The tall native grasses where the sparrows  nest had been overgrazed by cattle.

To replace the disappearing native grasses,  lovegrasses were introduced as cattle feed. Unfortunately the cattle didn’t love the  lovegrasses, so they kept eating the small   amounts of native grass that remained, allowing  the lovegrasses to spread faster than expected. But, helpfully for the Botteri’s sparrows,   these non-native lovegrasses put up “vacancy”  signs as they quickly swept across Arizona.

When the sparrows finally  returned to Arizona in the 1960s,   they were spotted nesting  in the invasive lovegrasses! Researchers initially worried the alien  grasses might be an “ecological trap”. In other words, although the sparrow  feels safe using the habitat,   it might not offer as much cover from  predators or facilitate healthy breeding.

But they found that birds nesting  in non-native grasses reproduced   at the same rates as birds nesting in native ones. So even though the native habitat will always  be the best home for the Botteri’s sparrow,   lovegrasses seem to be an acceptable alternative,  given the state of the grass-housing market. While these grasses were a highly  visible invader with big impact,   tiny critters can pack a powerful punch, too.

Such as the microbial invaders in the  Caribbean that are helping out corals. This probably isn’t breaking news to you,   but coral reefs are threatened by rising  temperatures and changing ocean chemistry. Their life is a little complicated, because  they rely on symbionts, tiny microbial partners.

In the corals’ case, they’re  algae that live in the coral   and make food for it by photosynthesizing. Like a little live-in grocery store. One species of symbiont, Symbiodinium trenchii,   has been spreading from the  Indo-Pacific to the Caribbean.

S. trenchii isn’t like other microbes. It’s better at photosynthesizing  under stressful conditions than   the local Caribbean algae are, so  it can tolerate higher temperatures. As a result, coral colonies infiltrated by S.  trenchii also do better when things get toasty.

It definitely sounds great that S. trenchii  helps corals withstand higher temperatures,   but there could be hidden costs tagging along. For example, in some colonies,   this invasive symbiont seems to change how  fast corals form their hard exoskeletons. So we’ll keep an eye on that for a bit  before declaring S. trenchii as a coral hero.

And it turns out that corals and  crocodiles have something in common,   because crocs also got a  little help from an invader… But before we tell you who, we need  a little help from this sponsor. This SciShow video is supported by DeleteMe,  the hands-free subscription service that removes   your personal information from hundreds  of data brokers and people search sites. SciShow’s executive producer, Nicole,   signed up this year and already  had 16 listings removed for her.

They also made it really easy for her to remove   additional listings herself  with the click of a button. Now she gets why DeleteMe has been the leading  expert in Personally Identifiable Information   removal for over 15 years and was recently named  by Wirecutter as the #1 data-removal service. Add her to a list of creators, election workers,   medical providers, and others who  trust DeleteMe with their data privacy.

You can join them using the QR code on screen   or at joindeleteme.com/SCISHOW with  the promo code SCISHOW at checkout. You’ll get 20% off DeleteMe US consumer plans. Australia’s feral pigs are the  descendents of 19th century domestic   pigs that were convicted of crimes  and then shipped off to Australia.

Just kidding, the pigs weren’t criminals,   they were just brought to Australia  as a food source for colonists. Today, there are about 23  million feral pigs in Australia. Feral pigs cause all kinds of environmental havoc,   from disturbing vegetation to spreading  weeds to wholescale habitat destruction.

But not everyone has a beef  with Australia’s feral pigs. Crocodiles find them quite useful! Until the 1970s, crocodile hunting was  unregulated in this part of the world,   and the croc population dwindled  to just a few thousand animals.

When the government realized how much danger they  were in, crocodiles were given protected status. That surely helped. But researchers think they got an  assist from those invasive pigs.

In 2022, scientists compared samples  of modern crocodile bones to those   of animals killed between 1968 and 1986. They found that the older crocodile bones  contained more specific isotopes of carbon   and nitrogen than the bones of  modern saltwater crocodiles. Higher abundance of those carbon and nitrogen  isotopes is associated with a fish-forward diet,   because seafood like catfish and  barramundi have more of those isotopes.

Aquatic wildlife was the traditional  fare of crocodiles in the past. But the decreased amounts of those carbon and  nitrogen isotopes in the modern crocs suggests that,   in the post-hunting era, crocs are  relying more on terrestrial prey. The invasive pigs probably account for a big chunk  of that land-based buffet, because they’re pretty   easy pickings: they’re plentiful, nutritious,  and often wallow in mud near croc territory.

This suggests the pigs have contributed  to the crocs’ resurgence Down Under! Speaking of Australia, our next  invader is a native Aussie. The eucalyptus tree first arrived  in California during the gold rush,   and quickly became a local landscaping darling.

Today, it’s seen for what it is: invasive. Large eucalyptus groves can affect  a microclimate’s temperature,   humidity, shading, and soil characteristics. But the eucalyptus tree is also offering a  big helping hand to California’s butterflies.

In California, 34% of native butterflies use   non-native plants for food  or as a place to lay eggs. Butterflies aren’t doing so well lately  because of widespread habitat loss. So any help they can get is welcome.

One of California’s most iconic butterflies,   the Monarch butterfly, is also  one of the most vulnerable. The population of monarchs that migrate up and   down the west coast has declined by  roughly 95 percent since the 1980s. Scientists put this population’s chance of   extinction before the year  2080 at roughly 99 percent.

That is pretty bleak. One of the major reasons for that  decline is loss of suitable habitat. These western monarchs usually spend  the winter on the coast of California.

They migrate during the day,  but roost in trees overnight. They specifically need trees with thick canopies  that maintain a comfortable temperature. Many of the large, native trees that fit that  bill have been removed by logging and development.

So western monarch butterflies have shifted  to roosting mostly in eucalyptus trees. They provide safety and  nectar for the butterflies,   giving them a better shot at survival. So I guess those silver-lined leaves  have an ecological silver-lining, too.

And we have another example for you of invasive  trees providing refuge for vulnerable species. This next tree may help protect a  native snail from a dangerous predator. The common Norway rat is probably  the one you’re most familiar with.

But the black rat is a different  species, native to India. In most places, they’ve been largely  out-competed by the Norway rat,   but black rats are still found on most  continents and are considered invasive. Japan in particular has a problem with black rats.

They wreak way more havoc than the typical ratty   shenanigans you’d expect  in attics and back alleys. Black rats also threaten native species,   including one of its favorite  snacks: the Japanese land snail. This is where our invasive tree steps in.

The drooping sheoak is also native  to Australia, just like eucalyptus. But now it’s found on Anijima, an uninhabited  island in Japan’s Ogasawara Archipelago. These trees’ destructive power is their ability  to form a homogenous, nearly impenetrable forest.

They grow fast, lay down a thick network of roots,  and drop a lot of litter on the forest floor,   which basically makes it impossible  for native plants to grow there. But that hostility to native plants also makes   them an excellent hiding  spot for those land snails. In fact, land snails dodge rats better in  the sheoak forests than in native vegetation.

Researchers think they might be hiding from the   black rats in the litter that  collects under these trees. Because when conservationists removed the trees,   they also found that the  snail population declined. So it seems like the sheoaks are giving  our snail friends some much needed shelter.

Although there are still a lot of reasons to  remove the sheoaks, researchers advocate for   addressing the black rat population first, to  give the land snails a better chance of surviving. And to wrap things up, we’re headed back  to Florida, you can’t escape. This time   we’re talking about their huge  problem with Burmese pythons.

These constrictors are native to southeast Asia,  but were imported to Florida by the pet trade. At some point, a few escaped captivity  or were deliberately released,   and they found that Florida’s  habitats suit them just fine. Today, officials say the Florida Everglades   are likely home to “tens of  thousands” of Burmese pythons.

They are not friendly neighbors. Burmese pythons have been  feeding on native species. For some species, their population has declined  as much as 95% since the pythons moved in.

But the snakes have actually been helpful  in one small way: they eat raccoons. Even though raccoons are native  Floridians, it’s kind of helpful   to have fewer of them because raccoons  eat the eggs of freshwater turtles. One research study found that  python-infested areas also had   much lower rates of predation on artificial  turtle nests, compared to areas without pythons.

And they’re pretty sure that’s  because pythons had eaten many   of the animals that do the turtle nest predation. Even though the pythons are indirectly  helping turtles and other egg-laying   species, it doesn’t negate the  other serious problems they cause. As you might have guessed, when it comes to  nature, there are no clear cut villains or heroes.

And although in many cases invasive  species have earned their bad reputation,   we can’t always assume that all  invasives are all bad all of the time. In fact, some scientists are trying  to quantify both the negative and   positive impacts of alien taxa using  hypothetical scenarios based on real data. This would let them categorize alien taxa’s  potential benefits from minimal to massive,   and allow conservationists to weigh the  pros and cons of evicting any invasives.

As is often the case, the full picture is complex. Scientists have learned that while  eradicating invasive species is usually   necessary to protect native species,  it should be approached with caution,   and only after considering all of the  invasive species’ helpful impacts, too. Because sometimes you can find a  friend in the most unexpected places. [♪ OUTRO]