Attack of The Alien Invaders

Attack of the alien invaders? Aliens are among us. Invasive alien species are a threat to human health and to every ecosystem on our planet. Sound like hyperbole? It’s not. 


I am still tempted to write about unidentified aerial intrusions aka Chinese spy balloons, the physics of how they stay aloft & their potential capabilities, but the news is too fresh for me to engage.

balloons w Ian hiding
Do you see me?

What is not fresh is the pervasive existence of invasive alien species. Not spy balloons, but invasive plants & animals not native to an ecosystem. And we don’t need to look up to find these alien invaders. Aliens are among us.


Invasive alien species are among the most damaging environmental forces on our planet. They’ve traveled with humans, colonizing even more places than we have.

Yet you may not know these alien invaders even exist! 

Kevin looking at a white board of Louie

The National Invasive Species Information Center, working under the US Department of Agriculture

defines invasive species as...

non-native (or alien) to the ecosystem under consideration and, whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

Definition of IS here

Before researching this article, I didn’t even know there was a National Invasive Species Info Center!

boys with pets

United Nation’s (UN) Intergovernmental Platform for Biodiversity and Ecosystem Services (IPBES) projected that about one fifth of the Earth’s surface, including the global biodiversity hotspots, are at risk due to attack of the alien invaders.

boys acting scary
We aren't afraid of alien invaders

Maybe those boys aren’t afraid of attacks by alien invaders, but I am, for our ecosystems.

These species can threaten the health of plants and animals, including humans. And they cause extensive economic harm. 

Let’s have a look at 10 of the most harmful invasive  species.


You could easily argue which 10 most harmful invasive species should be in the top 10. I had difficulty narrowing this down. I wanted diversity, & so I looked at plants, insects, mammals, amphibians, fish…well, you get the idea.

Alice and the lizard
Nope, that's a native species

1. YELLOW CRAZY ANTS (Anoplolepis gracilipes)

The yellow crazy ant has colloquially been given the modifier "crazy" because of the ant's erratic movements when disturbed. It is one of the largest invasive ant species in the world
The native crab population is under threat
Since 1990, yellow crazy ants have been responsible for the death of 10-20 million red land crabs on Christmas Island, Indian Ocean.
YCA & Crabs
The ants can temporarily blind nesting seabirds and injure chicks.
They are particularly harmful to young animals, such as small mammals, reptiles, amphibians and hatchling birds.
These ants affect humans, too.
The species has been known to occupy such agricultural systems as cinnamon, citrus, coffee and coconut plantations.
Because yellow crazy ants have generalized nesting habits, they are able to disperse via trucks, boats and other forms of human transport.
Yellow crazy ant aliens are among us & spreading
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Invasive alien species have had a profound impact on ecosystems all over the world. Their presence can lead to fundamental changes in the biodiversity of a given ecosystem as well as the extinction of native species, like the threatened Christmas Island Crabs. (Gecarcoidea natalis)

christmas island map


Islands are especially vulnerable to attacks by alien invaders
Island Ecosystem overview
Islands are more prone to invasion by alien species because of the lack of natural competitors and predators that control populations in their native ecosystems.
Islands often have ecological niches that have not been filled because of the distance from colonizing populations, also increasing the probability of successful invasions.
Many island species evolved in the absence of predators, meaning they don’t have defense mechanisms that other species might have, such as flight, camouflage, poison, or weaponry.
If invasive predators enter an island species’ habitat, the native species are not equipped to cope with the new threat.
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2. CANE TOAD (Rhinella marina )

Cane toads have successfully invaded ecosystems in many parts of the world where people have intentionally introduced them.
cane toad facts
Cane toads were introduced to Australia in the 1930s to control sugar cane pests.
Packed with poison, in glands above their eyes and, in the males, throughout their skin, these toads have made short work of some of Australia's native carnivores.
The bufadienolides in the toxin are cardiac glycosides that cause heart arrhythmias
Ultimately complete loss of normal myocardial electrical function occurs.
I can't say I'm a fan of crocodiles but
the goanna -- a big lizard; the carnivorous northern quoll -- a marsupial; & the freshwater crocodile have all fallen victim to the invasive alien species, losing substantial proportions of their populations to the toads.
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The toads have been run over with cars, bikes and lawn mowers, whacked with cricket bats and golf clubs, and frozen to death in fridges and freezers.

If you see one of these alien invaders, here is a guide to euthanize a cane toad.

Obviously this is a personal decision. I am only providing information.


In Australia, cane toads are a common sight in yards, golf courses, and school campuses.

Dogs and cats that attack or try to eat this highly toxic toad can be poisoned.

Dogs like terriers that readily attack small animals are especially vulnerable.


3. CATS (Felis catus)

Let's hope these beauties don't eat a cane toad, either. But...
On the flip side, cats kill ~ 2.4 billion birds every year in the U.S. alone
Cat as an invasive species
and cats kill 466,000,000 reptiles /yr in Australia
cats & reptiles
In California, 67% of rodents, 95% of birds, and 100% of lizards brought home by cats were native species, and native birds were twice as likely to be seen in areas without cats
USDA paper on free-ranging cats
Cats are a definitive host species of the parasite Toxoplasma gondii which causes toxoplasmosis.
Consequences of T. gondii infection in people, wildlife, & livestock vary but may include behavioral changes, blindness, & even death.
toxoplasmosis in humans
A single cat may excrete in its feces hundreds of millions of infectious T. gondii oocysts into the environment where any bird or mammal (intermediate host) may ingest or inhale them and become infected
Any cat that spends time outside is also at risk for contracting & spreading various parasites to livestock & pets. For example, outdoor cats have been implicated in the spread of plague & typhus via the proliferation of fleas.
parasitic infections from outdoor cats
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In 1894, a pregnant cat named Tibbles traveled with her owner to an untouched island south of New Zealand.

She was a non native = an invasive alien species. This island was the home for the Stephen Island wren (Traversia lyalli), a small flightless bird found only there.

Tibbles single-handedly caused the extinction of this wren.

Tibbles and the wren
Stephens Island of New Zealand
No more Stephens Wrens


Yes, another island vulnerability example w/ cats as our invasive alien species.

Louie coat
I'm wearing an alien clothing item but I am not an invasive alien species.
The only human inhabitants on Marion Island are the South African National Antarctic Program’s staff at a research station.
In 1949, when the new research buildings suffered a mouse infestation, five domestic cats were imported to dispatch the unwelcome rodents.
But someone forgot to have them neutered.
Within 30 years there were 2000 + feral cats on Marion Island, feasting not on mice but the very birds the scientists were there to study.
Feral cats were killing an estimated 450,000 seabirds each year, resulting in the local extinction of four species of storm- petrels and diving-petrels.
What did they do about the cats, aka an invasive alien species?
Major conservative action
The introduction of a feline panleucopaenia virus halved the number of cats by 1979. Sustained hunting & trapping over the next decade saw cats finally eradicated by 1991.
What can we do about invasive species ? Specifically feral cats?
PETA ideas for feral cats
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Looney Tunes may have profited with Tweedy Bird besting the cat, but in life, this is not the case.

Birds lose.

Check out a feel good post about how the robins in our backyard ruled!


Invasive alien invaders that are mammalian predators are arguably the most damaging group of alien animal species threatening global biodiversity. Thirty species of invasive predator are implicated in the extinction or endangerment of 738 vertebrate species—collectively contributing to 58% of all bird, mammal, and reptile extinctions.

With those stats, it makes me wonder how any other animals aside from mammals made my list of 10 most harmful invasive species!

alex afraid on a zip line
I hope there isn't an impeding attack of the alien invaders


Let’s look at another mammalian invasive alien species that isn’t quite as beloved at cats.

large group

4. RATS (Rattus rattus)

This invasive alien species of rodent inhabits every continent except for Antarctica.
Black rats, originally from the Indian subcontinent, spread to North America through marine shipping and hold a steady spot on the International Union for Conservation of Nature’s list of 100 World's Worst Invasive Species.
100 Worst Invasive Species List
Now you know why I had a tough time paring it down to the 10 most harmful invasive species
Rats transmit disease such as the plague bacterium
Obviously not good for humans!
Black Death
According to the Nature Conservancy, rats are responsible for 40-60 % of all bird and reptile extinctions on islands.
Nature Conservancy
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An unsettling photo below displaying a non-native rat, or an attack of alien invaders. In this example, the victim is a helpless New Zealand fantail chick.

I couldn’t be a wildlife photographer if I had to document the demise of a baby chick, even if it raises public awareness about alien invasive species. (Hm…I am posting the pics on this post, however!)

Rat attacking a new zealand fantail nest
Rat attacking a New Zealand fantail nest
New Zealand Fantail
New Zealand Fantail

5. AMERICAN MINK (Neogale vison)

The American Mink may seem like a random inclusion in my 10 most harmful invasive species post. I agree, but it tickled me that the decision by humans to farm minks for their coats ended up backfiring in such a spectacular fashion!

Again, these photographers must have strong stomachs. I'd be trying to help this chick.
American Minks were introduced to Great Britain in 1929 for use in fur farming
Individuals began to escape from farms and breed in the wild.
American minks are semi-aquatic, like the European water vole. You can guess what happened next...
Since the introduction of the American mink, the native water vole (Arvicola amphibius) has experienced one of the most rapid & serious declines of any British wild mammal during the 20th century.
Water voles under threat
There has been a decline in as much as 94 % in the number of water vole sites.
Predation by the invasive alien species --American mink-- is a key factor in this decline.
more on water voles here
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coral reef

6. LIONFISH (Pterois volitans & Pterois miles)

Native to the Indo-Pacific oceanic region, lionfish are quickly spreading throughout the coasts & coral reefs of the East Coast of the US.
Tracking Lionfish
Lionfish are voracious eaters.
The Lionfish’s stomach can expand up to 30 times its normal volume.
A 2008 study in the Bahamas calculated that lionfish arriving at a new reef can eliminate more than eighty per cent of other species within five weeks.
In addition to eating native reef fishes, they prey on crabs, shrimps, juvenile octopus, lobsters, sea horses, and squid, which are key to their ecosystems.
Octopus Facts!
Their venomous dorsal spines have helped to protect them from any natural predation in the Atlantic.
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When my family went diving in Grand Cayman, the instructors had pole spears with them. The dive instructors received ~ $6 for each lionfish they collected.

If you’re interested in helping with the removal of invasive alien species, the organization ENNDS, has training and outreach programs, along with links to learn more about invasive species in your area.

Pool work before the first ocean dive
Or we could donate?

Or we could eat them!

Lionfish are higher in heart healthy Omega 3 fatty acids, lower in saturated fats & mercury than many fish served in restaurants such as snapper, grouper, and tuna.

Here’s a list of a few restaurants that serve fresh lionfish!


seared lionfish dinner

I haven’t eaten lionfish but I’m willing! What I’m unwilling to eat is another water-based alien invasive species, this one in fresh water. 

7. ZEBRA MUSSELS (Dreissena polymorpha)

courtesy NOAA
Zebra mussels (Dreissena polymorpha) are small, freshwater, bivalve shellfish likely brought to the U.S. as stowaways in the ballast water of ships.
They are native to the Caspian and Black Seas south of Russia and Ukraine, and have since become widespread in both Europe and the U.S.
Zebra mussel summary
Zebra mussels are armed with root-like threads of protein, called "byssal threads," that allow them to firmly attach themselves to hard surfaces such as rocks, native mussels, docks, or boats.
Zebra mussels will also attach to native mussels!
In large enough numbers, zebra mussels can prevent the natives from moving, feeding, reproducing, or regulating water properly.
The zebra mussels outcompete the natives for food and space, & because of their fast reproduction can quickly overwhelm a water system.
Examples of non-agricultural economic impacts include blocking intake pipes for power generation and water treatment facilities, causing all manner of economic impact.
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I live near Lake Michigan and stepping on one of these mussels is no fun.

For more on the Science of Touch, click on the link below

Science of Touch

WHAT CAN WE DO ABOUT INVASIVE SPECIES? (in this case zebra mussels)

Once a population of zebra mussels has become established in a water body, there is very little to be done to remove them.

boys playing laser tag

This post may be getting a little too grim, so here is a success story about how research & a concerted effort by farmers and the authorities did stop an attack of the alien invaders. One invasive alien species erradicated!

balloon & Louie

8. PINK BOLLWORM (Pectinophora gossypiella)

In 2018, U.S. Secretary of Agriculture announced that U.S. cotton is free of the devastating pink bollworm.
In this case, fighting the attack of the alien invaders took 100 years!
This eradication of an invasive alien species took rigorous control & regulatory activities carried out by the USDA, state departments of agriculture, the U.S. cotton industry & growers.
PDF about pink bollworm
The pink bollworm was first detected in Texas in 1917.
arriving from northern Mexico through infested shipments.
Adults lay eggs on cotton bolls; once hatched, the larvae eat the seeds and damage the fibers of the cotton, reducing the yield and quality.
Bye bye pink bollworm!
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Our final two invasive alien species belong in the plant kingdom. Many invasive plants are still widely available in garden centers across the U.S.


Poor legislation!

louie smells the azaleas
Azaleas are not an invasive species
Results of a new study by ecologists at the University of Massachusetts Amherst show that 1,330 nurseries, garden centers and online retailers still offer 100s of invasive plant species as ornamental garden plants. This includes 20 species that are illegal to grow or sell nationwide.
States generally do a good job limiting sales of their own regulated plants, but there are major inconsistencies of what's being regulated across state borders.
Study of plant invaders still for sale

Aliens are among us! These alien invasive species don’t have any legs but they are attacking just the same. 

world map of Global threat of alien plant invaders
2016 PNAS study of countries threatened by plant invaders

9. WATER HYACINTH (Eichhornia crassipes )

Gorgeous, right?
My first search for the water hyacinth brought me lovely photos like that one, with descriptions such as Large Beautiful Purple Flowers! Provides Shade & Protection!
Sure, H2O hyacinths provide shade, but too much shade.
These invasive species block the sunlight & oxygen levels in water systems, which results in damaging water quality & seriously affecting various lifeforms in an ecosystem
H2O hyacinth facts
Their shade creates a favorable environment to produce snails & mosquitoes that cause diseases like Bilharzia & malaria.
In Lake Victoria, Uganda, H2O hyacinths grew so thickly that boats could not get through it. .
Some ports were closed.
In Lake Tana, the largest lake in Ethiopia, the H2O hyacinth infestation is a threat to the ecosystem.
attack of the alien invaders indeed!
H2O hyacinth Ethiopia
What can we do about invasive species like the water hyacinth?
Control strategies for established populations of invasive alien species can be costly and complex endeavors
One thing is certain: Don't plant them in your water garden!
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Invasive Plants success reasons


10. COGONGRASS (Imperata cylindrica)

Cogongrass is labeled one of “the world’s worst invasive weeds” by the USDA
Cogongrass facts
It is native to Southeast Asia & is a widespread invader in many subtropical and tropical regions
Cogongrass fact sheet
The sale of ornamental nonnative plants is a primary pathway of invasive plant introduction into the US.
invaders for sale
Cogongrass is a warm-season perennial grass considered among the worst invasive plants in the world.
IFAS facts
The ‘Red Baron’ cultivar of Imperata cylindrical has bright, showy, blood-red leaf edges.
It is frequently sold across the U.S. in plant nurseries and is widely available over the Internet for ornamental use.
It is often described as being non-invasive, although published proof of this claim is lacking.
What can we do about invasive species in this case cogongrass
Control of Cogongrass requires an integrated and well-timed strategy which includes herbicide application.
details here
Establishment of competing vegetation has been successful in controlling the spread of cogongrass.
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What can we do about invasive species ?

Referring now to invasive alien species of the plant variety?

Plant natives!

I understand! Ornamentals are so tempting & in the past, I've succumbed to the lure. Be strong!
Audubon guide to native plants

ALIENS ARE AMONG US! Watch a 2 minute youtube video produced by the Nature Conservatory w/ ideas to fight invasive alien species.

All my joking aside, the materials contained on these websites are provided for general information and educational purposes only and do not constitute professional advice on how to deal with alien invasive species.

If you have any questions, please contact your local wildlife authority. 

Which invasive alien species do you battle in your part of the world?

Have you eaten lionfish?


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Amy Laundrie
February 27, 2023 6:39 am

Hi Sue,
My area of Wisconsin deals with invasive garlic mustard. It was fascinating to learn about the invasive acquatic plants, toad, and ant–all of which were new to me. I’d forgotten about the mink. One attacked one of my pet ducks, so I’m not a fan of them.

Thanks for the great post again. I always enjoy your graphics and content.


February 27, 2023 7:52 am

I always learn so much from reading your posts! Alien species seem to be everywhere. Great post!

February 27, 2023 8:20 am

I would love to try lionfish. No more picking wildflowers for me. I don’t want to spread the seeds.Thanks for the helpful links for things we can do to combat invasive species!

Becki Kidd
Becki Kidd
February 27, 2023 8:34 am

Alligators & Pythons in areas they aren’t meant to occupy pose issues too. Hope you’re feeling better.

Eva Apelqvist
Eva Apelqvist
February 27, 2023 8:57 am

Sue, another great post. I really recommend Cane Toads: An Unnatural History about our role in spreading invasive species. It is excellent. Thank you again.

February 27, 2023 9:57 am

That cane toad is enormous! I would hate to have a poisonous anything in a public park. Great post, thank you!

Fransic verso
February 27, 2023 10:01 am

The Chinese spy balloon caused trouble and people were freaking out lol

Mummy Conquering Anxiety
Mummy Conquering Anxiety
February 27, 2023 1:10 pm

Such an interesting post, as always. it’s so fascinating reading about eco systems and how one tiny element can totally disrupt it all!

Thrift Plan Enjoy
Thrift Plan Enjoy
February 27, 2023 1:57 pm

Thank you such an informative post. I hadn’t heard of some of these creatures before!

Unwanted Life
February 27, 2023 3:36 pm

I really think cats should be required to wear bells on their collars by law to protect local wildlife. A species that didn’t make your list was catfish. I saw a documentary a few years back about how a river (I think it was in France) that has been taken over by nonnative catfish. The catfish have also learnt to hunt birds

February 27, 2023 7:03 pm

This is such an interesting post! As usual, I learned a lot from it. Thanks so much for sharing!

February 28, 2023 10:17 am

Very interesting as usual. Really liked the part about the plants since we have many of them in Wisconsin. Not real happy about the cat portion though the truth hurts at times. Can’t wait for the next posting.

Fadima Mooneira
March 1, 2023 5:25 am

It’s interesting to learn about these creatures. Thank you for sharing.

Lisa's Notebook
March 1, 2023 10:27 am

I’ve never considered cats to be an invasive species, but I can see how that poor little wren colony would disagree! I guess our invasive species (not that I have any in our garden, thankfully) is Japanese knotweed, which is capable of destroying building foundations, apparently, eek!

Baby Boomer Super Saver
Baby Boomer Super Saver
March 3, 2023 4:49 pm

This is an important topic that definitely needs more attention. I’ve known about the zebra mussels and the efforts to slow their progression to other bodies of water in the Midwest by checking boats & other measures. But it takes education & effort by boat owners & water enthusiasts to stay on top of this. In California, we are overrun by the invasive broom plant. The yellow flowers may look pretty, but the plant chokes out all the other native species.

March 4, 2023 2:45 pm

This was really interesting post. I haven’t eaten Lionfish before x

Susan Berk Koch author

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