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Releasing Invasive Species on Purpose
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Uploaded: | 2023-03-07 |
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Over the centuries, to fight invasive species, some people have considered using... more invasive species. It's called biological control, and even though many early attempts were disastrous, it can actually work to protect agriculture and native plants and animals.
Hosted by: Hank Green (he/him)
----------
Support SciShow by becoming a patron on Patreon: https://www.patreon.com/scishow
----------
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever: Matt Curls, Alisa Sherbow, Dr. Melvin Sanicas, Harrison Mills, Adam Brainard, Chris Peters, charles george, Piya Shedden, Alex Hackman, Christopher R, Boucher, Jeffrey Mckishen, Ash, Silas Emrys, Eric Jensen, Kevin Bealer, Jason A Saslow, Tom Mosner, Tomás Lagos González, Jacob, Christoph Schwanke, Sam Lutfi, Bryan Cloer
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Sources:
Velivelli et al 2014, "Biological control agents: from field to market, problems, and challenges"
https://doi.org/10.1007/s10526-017-9831-y
http://www.jstor.org/stable/3868683
https://digitalcommons.unl.edu/cgi/viewcontent.cgi?referer=https://en.wikipedia.org/&httpsredir=1&article=1027&context=bioscilouda
https://Hawai'ibirdingtrails.Hawai'i.gov/bird/common-myna/ (Myna birds)
https://content.ces.ncsu.edu/rosey-wolf-snail
https://www.fs.usda.gov/psw/topics/biocontrol/strawberryguava/biocontrol.shtml#:~:text=In%20Hawai'i%2C%20biocontrol%20has%20been,Klamath%20weed%2C%20and%20ivy%20gourd.
https://dlnr.Hawai'i.gov/hisc/info/biocontrol/latest-biocontrol/
https://mauiinvasive.org/2012/04/18/moving-on-from-the-mongoose-the-succuss-of-biological-control-in-Hawai'i/
https://www.agric.wa.gov.au/biological-control/biological-control-declared-plants#:~:text=Biological%20control%20can%20never%20eradicate,to%20individual%20properties%20or%20paddock.
https://www.esf.edu/efb/parry/invasivesseminar_readings/Simberloff_2012.pdf
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https://www.sciencedirect.com/science/article/abs/pii/S1049964412001727
https://researchspace.auckland.ac.nz/handle/2292/58529
https://dlnr.Hawai'i.gov/removerats/home/impacts-of-rodents-mongooses/
https://dlnr.Hawai'i.gov/forestry/files/2013/09/SWARS-Issue-6.pdf
https://entnemdept.ufl.edu/creatures/bfly/cactus_moth.htm
https://ipm.ucanr.edu/PMG/PESTNOTES/pn7410.html
https://books.google.com/books?id=QvOPufXCJq0C&pg=PA221#v=onepage&q&f=false
https://hilgardia.ucanr.edu/fileaccess.cfm?article=152759&p=FNUASH
https://biocontrol.ucr.edu/cottony-cushion-scale
https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/1540-9295%282006%29004%5B0132%3ABCOISS%5D2.0.CO%3B2
https://neobiota.pensoft.net/article/66276/
https://digitalcommons.unl.edu/cgi/viewcontent.cgi?referer=https://en.wikipedia.org/&httpsredir=1&article=1027&context=bioscilouda
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7410.html
https://conbio.onlinelibrary.wiley.com/doi/10.1111/csp2.296
https://www.sciencedaily.com/releases/2008/05/080508131953.htm
Image Sources:
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https://tinyurl.com/59zs95bj
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https://tinyurl.com/3ppp3vhr
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https://tinyurl.com/ykcxsaz9
https://tinyurl.com/3wsywcvb
https://tinyurl.com/bdeymtn5
https://tinyurl.com/3zhezsaz
https://tinyurl.com/ms3tj9p5
https://tinyurl.com/3ry8pvrz
https://tinyurl.com/ycktamtb
https://tinyurl.com/33zay92u
https://tinyurl.com/2u36w58x
https://tinyurl.com/2j646bcd
https://tinyurl.com/384xw2t2
https://commons.wikimedia.org/wiki/File:Starr_070205_4082_acacia_koa2.jpg
https://commons.wikimedia.org/wiki/File:Starr_040713-0079_Cibotium_menziesii.jpg
https://tinyurl.com/39u54bdm
https://tinyurl.com/8axus23r
https://commons.wikimedia.org/wiki/File:Astonished.jpg
https://commons.wikimedia.org/wiki/File:Kingdavidkalakaua_dust.jpg
https://commons.wikimedia.org/wiki/File:William_Hillebrand_(PP-72-8-012).jpg
https://tinyurl.com/bdemczaa
https://tinyurl.com/2p8e3yjc
https://tinyurl.com/2uywvrzx
https://tinyurl.com/3tzp6rbv
https://tinyurl.com/2twpt96z
https://tinyurl.com/yc56bs38
https://tinyurl.com/mwrpwz7e
https://tinyurl.com/mwyexa95
https://tinyurl.com/bddjnjes
https://tinyurl.com/3vxf72f4
https://tinyurl.com/u236r29n
https://tinyurl.com/y7kw5exc
https://tinyurl.com/ycyh4822
https://tinyurl.com/yc6w48ym
https://www.inaturalist.org/observations/131807665
https://tinyurl.com/mr2vxn5t
Over the centuries, to fight invasive species, some people have considered using... more invasive species. It's called biological control, and even though many early attempts were disastrous, it can actually work to protect agriculture and native plants and animals.
Hosted by: Hank Green (he/him)
----------
Support SciShow by becoming a patron on Patreon: https://www.patreon.com/scishow
----------
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever: Matt Curls, Alisa Sherbow, Dr. Melvin Sanicas, Harrison Mills, Adam Brainard, Chris Peters, charles george, Piya Shedden, Alex Hackman, Christopher R, Boucher, Jeffrey Mckishen, Ash, Silas Emrys, Eric Jensen, Kevin Bealer, Jason A Saslow, Tom Mosner, Tomás Lagos González, Jacob, Christoph Schwanke, Sam Lutfi, Bryan Cloer
----------
Looking for SciShow elsewhere on the internet?
SciShow Tangents Podcast: https://scishow-tangents.simplecast.com/
TikTok: https://www.tiktok.com/@scishow
Twitter: http://www.twitter.com/scishow
Instagram: http://instagram.com/thescishowFacebook: http://www.facebook.com/scishow
#SciShow #science #education #learning #complexly
----------
Sources:
Velivelli et al 2014, "Biological control agents: from field to market, problems, and challenges"
https://doi.org/10.1007/s10526-017-9831-y
http://www.jstor.org/stable/3868683
https://digitalcommons.unl.edu/cgi/viewcontent.cgi?referer=https://en.wikipedia.org/&httpsredir=1&article=1027&context=bioscilouda
https://Hawai'ibirdingtrails.Hawai'i.gov/bird/common-myna/ (Myna birds)
https://content.ces.ncsu.edu/rosey-wolf-snail
https://www.fs.usda.gov/psw/topics/biocontrol/strawberryguava/biocontrol.shtml#:~:text=In%20Hawai'i%2C%20biocontrol%20has%20been,Klamath%20weed%2C%20and%20ivy%20gourd.
https://dlnr.Hawai'i.gov/hisc/info/biocontrol/latest-biocontrol/
https://mauiinvasive.org/2012/04/18/moving-on-from-the-mongoose-the-succuss-of-biological-control-in-Hawai'i/
https://www.agric.wa.gov.au/biological-control/biological-control-declared-plants#:~:text=Biological%20control%20can%20never%20eradicate,to%20individual%20properties%20or%20paddock.
https://www.esf.edu/efb/parry/invasivesseminar_readings/Simberloff_2012.pdf
https://www.sciencedirect.com/science/article/pii/S2214574520300304
https://www.sciencedirect.com/science/article/abs/pii/S1049964409000632
https://www.sciencedirect.com/science/article/abs/pii/S1049964412001727
https://researchspace.auckland.ac.nz/handle/2292/58529
https://dlnr.Hawai'i.gov/removerats/home/impacts-of-rodents-mongooses/
https://dlnr.Hawai'i.gov/forestry/files/2013/09/SWARS-Issue-6.pdf
https://entnemdept.ufl.edu/creatures/bfly/cactus_moth.htm
https://ipm.ucanr.edu/PMG/PESTNOTES/pn7410.html
https://books.google.com/books?id=QvOPufXCJq0C&pg=PA221#v=onepage&q&f=false
https://hilgardia.ucanr.edu/fileaccess.cfm?article=152759&p=FNUASH
https://biocontrol.ucr.edu/cottony-cushion-scale
https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/1540-9295%282006%29004%5B0132%3ABCOISS%5D2.0.CO%3B2
https://neobiota.pensoft.net/article/66276/
https://digitalcommons.unl.edu/cgi/viewcontent.cgi?referer=https://en.wikipedia.org/&httpsredir=1&article=1027&context=bioscilouda
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7410.html
https://conbio.onlinelibrary.wiley.com/doi/10.1111/csp2.296
https://www.sciencedaily.com/releases/2008/05/080508131953.htm
Image Sources:
https://tinyurl.com/msmhac3m
https://tinyurl.com/59zs95bj
https://tinyurl.com/fcmzzu7m
https://tinyurl.com/4wx9h3vn
https://tinyurl.com/3ppp3vhr
https://tinyurl.com/5n8z7v6h
https://tinyurl.com/ykcxsaz9
https://tinyurl.com/3wsywcvb
https://tinyurl.com/bdeymtn5
https://tinyurl.com/3zhezsaz
https://tinyurl.com/ms3tj9p5
https://tinyurl.com/3ry8pvrz
https://tinyurl.com/ycktamtb
https://tinyurl.com/33zay92u
https://tinyurl.com/2u36w58x
https://tinyurl.com/2j646bcd
https://tinyurl.com/384xw2t2
https://commons.wikimedia.org/wiki/File:Starr_070205_4082_acacia_koa2.jpg
https://commons.wikimedia.org/wiki/File:Starr_040713-0079_Cibotium_menziesii.jpg
https://tinyurl.com/39u54bdm
https://tinyurl.com/8axus23r
https://commons.wikimedia.org/wiki/File:Astonished.jpg
https://commons.wikimedia.org/wiki/File:Kingdavidkalakaua_dust.jpg
https://commons.wikimedia.org/wiki/File:William_Hillebrand_(PP-72-8-012).jpg
https://tinyurl.com/bdemczaa
https://tinyurl.com/2p8e3yjc
https://tinyurl.com/2uywvrzx
https://tinyurl.com/3tzp6rbv
https://tinyurl.com/2twpt96z
https://tinyurl.com/yc56bs38
https://tinyurl.com/mwrpwz7e
https://tinyurl.com/mwyexa95
https://tinyurl.com/bddjnjes
https://tinyurl.com/3vxf72f4
https://tinyurl.com/u236r29n
https://tinyurl.com/y7kw5exc
https://tinyurl.com/ycyh4822
https://tinyurl.com/yc6w48ym
https://www.inaturalist.org/observations/131807665
https://tinyurl.com/mr2vxn5t
Thanks to Brilliant for supporting this SciShow video!
As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. [♪ INTRO] Look at this cute, adorable, fuzzy little mongoose. It is a horrendous pest and a nuisance and anyone who lives in Hawai’i will tell you: Do not be fooled by those beady little eyes. Mongooses are not indigenous to the islands, but they live there now thanks to a failed attempt at pest control.
And yet, today, despite many catastrophic and well-publicized failures, some people say that using invasive animals as pest control is cost-effective, self-sustaining, and preferable to pesticides. Even in Hawai’i. To call this debate controversial would be an understatement. But at the end of this video, you should understand why anybody would advocate for doing this.
So let’s take a careful look at the successes and failures of this strategy, called biological control, the arguments for and against, and what we have learned that can help us do a better job of it. The term biological control covers a broad category of techniques. It can refer to things like conserving native predators to keep pests down.
But we’re going to focus on what people generally mean when they use the term: an attempt to control a particular pest species, usually an invasive one, by introducing new predators to the ecosystem. You see, humans have had this habit of introducing new pests to different areas, on purpose or accidentally. Rats, for instance.
We’ve brought rats to many islands via ships, including Hawai’i. Now in the places they originally evolved, rats might not have been a big problem. “Pests” is, after all, a word with a lot of human judgment attached. In those places, rats were part of a whole ecosystem, complete with predators to keep them in check, like owls or foxes or cats.
But in a new place, like the islands of Hawai'i, those naturally rat-eating predators aren’t present. And without the pressure those native predators put on the rats’ numbers, their population can explode and start really messing things up. Humans might dislike rats because they eat the food we’re growing, but rats also are a danger to many of Hawai'i’s native birds.
They’ve caused plants to disappear by eating all their seeds. They even eat sea turtle eggs. And rats are just one example. There are plenty of invasive species out there. Now, we can try to control rat numbers with traps, or hunting, or even poison, but these can be difficult to use.
Rats are often pretty good at avoiding traps, for instance, and putting rat poison all over the forest would be difficult, expensive, and, you know, there are other animals out there who we definitely don’t want to poison. So one idea to control rat numbers is to bring in some of those rat-eating predators instead, since not having them around kind of led to the problem in the first place. This is the basic idea behind biological control, as we have defined it. The predator, or sometimes a disease-causing pathogen, puts pressure back on the introduced species.
That’s a key point, since predator-prey interactions in nature basically never wipe out the prey species. Think of it more like a thumb on the scale, where the predator can manage the prey population enough that it’s no longer a problem. To be fair, it doesn’t always work out that way. One study, looking at using insects to control other insects, found that only 11% of attempts achieved complete control. Most of the time, the control agent couldn’t establish itself well enough in the ecosystem to work and just kind of died off.
But when it does work, biological control can be very effective. And, better yet, it can be self-sustaining, meaning you only have to do it once. If you were using rat poison, you might have to hire a bunch of people every year to go out and spread bait.
But predators can just kind of refresh the program themselves every time they have babies, with their numbers expanding and contracting as prey populations change. Now, that might all sound really nice. You’re restoring balance by having both prey and predator, right? But as elegant as this may sound, if you ask Hawai'ians about it, well, they may have some other ideas.
In fact, let’s talk about Hawai'i in depth real quick. Because Hawai'i has some of the biggest history with this whole scheme, for both good and bad. Now, Hawai'i, of course, is an island chain. Very far out in the ocean away from everything else, and it consequently has a lot of really unique species there. Endemic species, or the kind of things that aren’t found anywhere else.
You’ve got birds like the i’iwi and the pueo, mammals like the Hawai'ian monk seal, and a ton of different plants like the koa tree or the hāpuʻu tree fern. These islands may in fact be home to more than 10,000 unique forms of life. But, notably, none of those species are mongooses, which are originally found in Africa, Southern Europe, and the southerly parts of Asia. They are never found in the middle of the Pacific Ocean.
The story goes that, back in the 1880’s, there were a bunch of plantation owners on the Big Island who were all in an association together. They were upset about rats in their sugar cane fields and got the idea from basically some dude in the Caribbean to introduce mongooses to their fields. So they did. And the idea spread to other Hawai'ian islands. But then the whole idea backfired.
Mongooses don’t just eat rats. They eat a lot of things, including some of those really cool native species. And once the mongoose was out of the bag, so to speak, there wasn’t any putting them back.
They spread and went off into the wild and had little mongoose babies and they are now just kind of there, even today. And at the time it was totally legal to do this! No regulations existed until 1890, when King Kalākaua of Hawai'i passed some laws, but by then it was too late.
And this wasn’t the only example. One person, William Hillebrand, privately introduced the mynah bird to Hawai'i in 1865 to control army worms. Today, they compete with native birds for food.
And of course, Hawai'i isn’t the only place this has played out. Cane toads in Australia may be the most famous example of biological control gone wrong. Introduced from South America to control beetle infestations, they instead killed a bunch of native creatures.
They didn’t even eat the beetles. In fact, they may have made it worse by eating the few species that were eating the beetles already. So yes, there’s a lot of examples of biological control going bad, often due to the hasty introduction of generalists, species who are able to eat or affect multiple prey species.
Cane toads are often said to eat anything they can fit their mouth around. And today, we know in hindsight that even without direct predation for a control agent to mess up an ecosystem. For example, the control agents themselves might end up as unexpected food sources for nearby predators.
There was a case where scientists introduced a type of fly to an area, only for the nearby deer mice to end up developing a taste for them. The influx of new food made mouse numbers more than double, much to the dismay of everything else that the mice liked to eat. It’s also possible that, even though a certain agent might be fine here and now, that things will change in the future.
Critters can spread beyond the original release area, or climate change may force them to move. Today, some of the worst invasive species anywhere were introduced as biological control agents. So it makes sense that people would be hesitant.
But in kind of a mid-episode twist, it has worked sometimes. Even in Hawai'i. For instance, one of the invasive species that’s come to Hawai'i is the prickly pear cactus.
Prickly pears are native to the American tropics. They were likely introduced to Hawai'i sometime around 1809, and quickly took over large areas in some of the drier parts of the islands. In the 1940’s and 50’s, scientists looked at a couple of different species to try to control the cactus, including the cactus moth Cactoblastis.
This time they actually tested a bunch of candidate species before picking one to release, which is nice since it turned out some of the candidates also liked eating pineapple. Which aren’t native to Hawai’i either, but we like them because it’s pineapple, but I digress. The cactus moths worked and they’ve been keeping prickly pear in check ever since. They’ve even been used in other places too, like India.
Another invasive plant, strawberry guava, was controlled after a 2005 release of a scale insect. In that case, researchers took a whole 15 years to investigate it before daring to release the insect. Elsewhere, ladybugs and a type of fly have been credited with saving the California citrus industry from a pest called cottony cushion scale.
Then there’s cassava, a staple food that feeds 200 million people in sub-Saharan Africa. 50% of it was wiped out by the cassava mealybug, until the bug was brought under control by a biological control agent. So there are examples of biological controls seeming to work fairly well, and without major negative consequences to the rest of the environment. So the question then becomes, what made these biological controls work where the others didn’t?
For one thing, unlike those early releases in the 1800’s by just, like, anybody who felt like doing it, biological control is now usually subject to regulation and enforcement. In the United States, there were major laws passed in the 1970’s, such as the National Environmental Policy Act. Many countries require risk assessments now before signing off on any real-life experiments.
We’ve gotten much pickier about what makes a good biological control agent as well. Do not use generalists, for one thing. Today, scientists need to do some sort of test with relevant native species to see if the agent will affect them.
If you’re looking for something to control a plant, for instance, you’d need to do tests where you give candidates the option to feed, lay eggs on, or grow on the target plant. You’d also give them the option to choose other plants that are present in the area, and hope they don’t. This may mean looking at several dozen candidates.
Some scientists have also suggested expanding this process to include examining things like how the critters behave, or the chemicals they might give off, to understand as many potential interactions with the environment as possible. Scientists may also use models to predict what populations may look like years down the road and follow up with post-release monitoring to confirm. That is not to say the process is now foolproof.
In the 1960’s, a type of weevil was introduced to Canada to try to control an invasive thistle. Scientists thought these weevils were specialists, but it turned out they’re not and it began to attack native thistles as well. The scientists had tested the weevil before, but blind spots in how they set up the tests meant they didn’t realize there was a problem until it was too late. So mistakes can still be made. Systems must still be refined.
And that leaves us with a question: is biological control a good idea? Well, I mean, ideally, we’d just stop introducing invasive species, period. But some are already here, and we cannot go back in time.
Proponents of biological control say it’s better than letting invasive species wreck things. And they do appear to have helped save Hawai'i from a few invasive species. We have examples that they can point to where things seem to have worked out.
What’s more, modern examples of biological control have a much better track record than the days of doing whatever popped into your head. But it requires a lot of study to get this right. And if you don’t, it is usually a mistake that you are never able to take back, as those mongooses know very well. This SciShow video is supported by Brilliant. Brilliant is an interactive online learning platform with thousands of lessons in science, computer science, and math, starting with their course on Mathematical Fundamentals and going literally to Infinity, like a course about infinity.
And those mathematical fundamentals can help you calculate and wrap your mind around how many animals Hawai’i could end up with when an invasive population goes unchecked. This course uses puzzles and treasure hunts to guide you through variables, rates, and sequences. So you can learn middle school math concepts in a way that a middle schooler, or anyone else for that matter, would actually enjoy.
Brilliant is giving these learning tools to you for free for 30 days! After that, you can take 20% off an annual premium Brilliant subscription by clicking the link in the description down below or going to Brilliant.org/SciShow. Thanks for watching! [♪ OUTRO]
As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. [♪ INTRO] Look at this cute, adorable, fuzzy little mongoose. It is a horrendous pest and a nuisance and anyone who lives in Hawai’i will tell you: Do not be fooled by those beady little eyes. Mongooses are not indigenous to the islands, but they live there now thanks to a failed attempt at pest control.
And yet, today, despite many catastrophic and well-publicized failures, some people say that using invasive animals as pest control is cost-effective, self-sustaining, and preferable to pesticides. Even in Hawai’i. To call this debate controversial would be an understatement. But at the end of this video, you should understand why anybody would advocate for doing this.
So let’s take a careful look at the successes and failures of this strategy, called biological control, the arguments for and against, and what we have learned that can help us do a better job of it. The term biological control covers a broad category of techniques. It can refer to things like conserving native predators to keep pests down.
But we’re going to focus on what people generally mean when they use the term: an attempt to control a particular pest species, usually an invasive one, by introducing new predators to the ecosystem. You see, humans have had this habit of introducing new pests to different areas, on purpose or accidentally. Rats, for instance.
We’ve brought rats to many islands via ships, including Hawai’i. Now in the places they originally evolved, rats might not have been a big problem. “Pests” is, after all, a word with a lot of human judgment attached. In those places, rats were part of a whole ecosystem, complete with predators to keep them in check, like owls or foxes or cats.
But in a new place, like the islands of Hawai'i, those naturally rat-eating predators aren’t present. And without the pressure those native predators put on the rats’ numbers, their population can explode and start really messing things up. Humans might dislike rats because they eat the food we’re growing, but rats also are a danger to many of Hawai'i’s native birds.
They’ve caused plants to disappear by eating all their seeds. They even eat sea turtle eggs. And rats are just one example. There are plenty of invasive species out there. Now, we can try to control rat numbers with traps, or hunting, or even poison, but these can be difficult to use.
Rats are often pretty good at avoiding traps, for instance, and putting rat poison all over the forest would be difficult, expensive, and, you know, there are other animals out there who we definitely don’t want to poison. So one idea to control rat numbers is to bring in some of those rat-eating predators instead, since not having them around kind of led to the problem in the first place. This is the basic idea behind biological control, as we have defined it. The predator, or sometimes a disease-causing pathogen, puts pressure back on the introduced species.
That’s a key point, since predator-prey interactions in nature basically never wipe out the prey species. Think of it more like a thumb on the scale, where the predator can manage the prey population enough that it’s no longer a problem. To be fair, it doesn’t always work out that way. One study, looking at using insects to control other insects, found that only 11% of attempts achieved complete control. Most of the time, the control agent couldn’t establish itself well enough in the ecosystem to work and just kind of died off.
But when it does work, biological control can be very effective. And, better yet, it can be self-sustaining, meaning you only have to do it once. If you were using rat poison, you might have to hire a bunch of people every year to go out and spread bait.
But predators can just kind of refresh the program themselves every time they have babies, with their numbers expanding and contracting as prey populations change. Now, that might all sound really nice. You’re restoring balance by having both prey and predator, right? But as elegant as this may sound, if you ask Hawai'ians about it, well, they may have some other ideas.
In fact, let’s talk about Hawai'i in depth real quick. Because Hawai'i has some of the biggest history with this whole scheme, for both good and bad. Now, Hawai'i, of course, is an island chain. Very far out in the ocean away from everything else, and it consequently has a lot of really unique species there. Endemic species, or the kind of things that aren’t found anywhere else.
You’ve got birds like the i’iwi and the pueo, mammals like the Hawai'ian monk seal, and a ton of different plants like the koa tree or the hāpuʻu tree fern. These islands may in fact be home to more than 10,000 unique forms of life. But, notably, none of those species are mongooses, which are originally found in Africa, Southern Europe, and the southerly parts of Asia. They are never found in the middle of the Pacific Ocean.
The story goes that, back in the 1880’s, there were a bunch of plantation owners on the Big Island who were all in an association together. They were upset about rats in their sugar cane fields and got the idea from basically some dude in the Caribbean to introduce mongooses to their fields. So they did. And the idea spread to other Hawai'ian islands. But then the whole idea backfired.
Mongooses don’t just eat rats. They eat a lot of things, including some of those really cool native species. And once the mongoose was out of the bag, so to speak, there wasn’t any putting them back.
They spread and went off into the wild and had little mongoose babies and they are now just kind of there, even today. And at the time it was totally legal to do this! No regulations existed until 1890, when King Kalākaua of Hawai'i passed some laws, but by then it was too late.
And this wasn’t the only example. One person, William Hillebrand, privately introduced the mynah bird to Hawai'i in 1865 to control army worms. Today, they compete with native birds for food.
And of course, Hawai'i isn’t the only place this has played out. Cane toads in Australia may be the most famous example of biological control gone wrong. Introduced from South America to control beetle infestations, they instead killed a bunch of native creatures.
They didn’t even eat the beetles. In fact, they may have made it worse by eating the few species that were eating the beetles already. So yes, there’s a lot of examples of biological control going bad, often due to the hasty introduction of generalists, species who are able to eat or affect multiple prey species.
Cane toads are often said to eat anything they can fit their mouth around. And today, we know in hindsight that even without direct predation for a control agent to mess up an ecosystem. For example, the control agents themselves might end up as unexpected food sources for nearby predators.
There was a case where scientists introduced a type of fly to an area, only for the nearby deer mice to end up developing a taste for them. The influx of new food made mouse numbers more than double, much to the dismay of everything else that the mice liked to eat. It’s also possible that, even though a certain agent might be fine here and now, that things will change in the future.
Critters can spread beyond the original release area, or climate change may force them to move. Today, some of the worst invasive species anywhere were introduced as biological control agents. So it makes sense that people would be hesitant.
But in kind of a mid-episode twist, it has worked sometimes. Even in Hawai'i. For instance, one of the invasive species that’s come to Hawai'i is the prickly pear cactus.
Prickly pears are native to the American tropics. They were likely introduced to Hawai'i sometime around 1809, and quickly took over large areas in some of the drier parts of the islands. In the 1940’s and 50’s, scientists looked at a couple of different species to try to control the cactus, including the cactus moth Cactoblastis.
This time they actually tested a bunch of candidate species before picking one to release, which is nice since it turned out some of the candidates also liked eating pineapple. Which aren’t native to Hawai’i either, but we like them because it’s pineapple, but I digress. The cactus moths worked and they’ve been keeping prickly pear in check ever since. They’ve even been used in other places too, like India.
Another invasive plant, strawberry guava, was controlled after a 2005 release of a scale insect. In that case, researchers took a whole 15 years to investigate it before daring to release the insect. Elsewhere, ladybugs and a type of fly have been credited with saving the California citrus industry from a pest called cottony cushion scale.
Then there’s cassava, a staple food that feeds 200 million people in sub-Saharan Africa. 50% of it was wiped out by the cassava mealybug, until the bug was brought under control by a biological control agent. So there are examples of biological controls seeming to work fairly well, and without major negative consequences to the rest of the environment. So the question then becomes, what made these biological controls work where the others didn’t?
For one thing, unlike those early releases in the 1800’s by just, like, anybody who felt like doing it, biological control is now usually subject to regulation and enforcement. In the United States, there were major laws passed in the 1970’s, such as the National Environmental Policy Act. Many countries require risk assessments now before signing off on any real-life experiments.
We’ve gotten much pickier about what makes a good biological control agent as well. Do not use generalists, for one thing. Today, scientists need to do some sort of test with relevant native species to see if the agent will affect them.
If you’re looking for something to control a plant, for instance, you’d need to do tests where you give candidates the option to feed, lay eggs on, or grow on the target plant. You’d also give them the option to choose other plants that are present in the area, and hope they don’t. This may mean looking at several dozen candidates.
Some scientists have also suggested expanding this process to include examining things like how the critters behave, or the chemicals they might give off, to understand as many potential interactions with the environment as possible. Scientists may also use models to predict what populations may look like years down the road and follow up with post-release monitoring to confirm. That is not to say the process is now foolproof.
In the 1960’s, a type of weevil was introduced to Canada to try to control an invasive thistle. Scientists thought these weevils were specialists, but it turned out they’re not and it began to attack native thistles as well. The scientists had tested the weevil before, but blind spots in how they set up the tests meant they didn’t realize there was a problem until it was too late. So mistakes can still be made. Systems must still be refined.
And that leaves us with a question: is biological control a good idea? Well, I mean, ideally, we’d just stop introducing invasive species, period. But some are already here, and we cannot go back in time.
Proponents of biological control say it’s better than letting invasive species wreck things. And they do appear to have helped save Hawai'i from a few invasive species. We have examples that they can point to where things seem to have worked out.
What’s more, modern examples of biological control have a much better track record than the days of doing whatever popped into your head. But it requires a lot of study to get this right. And if you don’t, it is usually a mistake that you are never able to take back, as those mongooses know very well. This SciShow video is supported by Brilliant. Brilliant is an interactive online learning platform with thousands of lessons in science, computer science, and math, starting with their course on Mathematical Fundamentals and going literally to Infinity, like a course about infinity.
And those mathematical fundamentals can help you calculate and wrap your mind around how many animals Hawai’i could end up with when an invasive population goes unchecked. This course uses puzzles and treasure hunts to guide you through variables, rates, and sequences. So you can learn middle school math concepts in a way that a middle schooler, or anyone else for that matter, would actually enjoy.
Brilliant is giving these learning tools to you for free for 30 days! After that, you can take 20% off an annual premium Brilliant subscription by clicking the link in the description down below or going to Brilliant.org/SciShow. Thanks for watching! [♪ OUTRO]