Invasive/Introduced organisms in a very localized place

Recently here in North Georgia I came across a spider which I assumed to be a native golden silk orbweaver, but another naturalist confirmed it was a Jorō spider. I later found out that this species is actually native to Japan and the Southeast Asian coast…but only within the last few years did a population establish itself entirely in this one relatively small, localized part of Georgia. That struck me as very interesting.

What other organisms have you observed that share this characteristic?


The Asian Shaggy Digger Bee is a species that is established in the US only in the Washington DC metropolitan area and nearby areas. I’m trying to think of a few other species (there are tons of localized invasives in places like south Florida, mostly lizards, but I’m trying to think of others from other areas).


I’ve been studying Kalopanax septemlobus, a tree from East Asia that is very rarely planted as an ornamental in botanical gardens and in the gardens of eccentric gardeners here in the US. It takes many years (10 - 20?) to get large enough to set seed, but when it does, birds eat the berries and spread them around, resulting in numerous seedlings. One specific park in my area has just countless trees of this species of all ages, and for the longest time I was trying to figure out where they had come from. Turns out a single old estate near the park has two enormous specimens, probably planted in the early 1900s. If you look at the map for this species, you can see “hotspots” all over the Northeastern part of the US. Each spot has a story, usually connected to a single tree planted at an Arboretum or Botanical Garden. Boston in particular is overrun, as the Arnold Arboretum was one of the first places in the country to acquire the species, and they had several large specimens for many years. They’ve since removed all but one to stem the spread. I created a project to monitor the plant in my area.


Interesting that the recent spread of Joro Spiders looks quite similar to the spread of kudzu bugs which seemingly started out in the same region of Georgia. Not localized anymore, though.


The harvestman species Dicranopalpus ramosus has only been established in North America in the town of Cannon Beach, Oregon. Similarly, Opilio canestrinii is established only in the vicinity of Tsawwassen and Ladner in British Columbia, although I suspect this species may quickly spread to other areas in the PNW. On the west coast, Nemastoma lugubre is established only within the Iona Island regional park, near the Vancouver airport, although there are more populations in the eastern US and Canada. There are also 2 introduced species of Cosmetid harvestmen established in Miami. All of these populations were first (and so far only) documented by iNat observations.


Florida is full of these. Leiolepis belliana is one of my favorites, established in a 6 by 6 block radius in the neighborhood of Sunset, Florida. Most of our chameleon species are also known from extremely localized, introduced populations. Phelsuma laticuada is another fun one, known from an approximately one acre plot in Key West, Florida, though other equally tiny populations have been noted on the peninsula. I am currently studying localized millipede populations, though these are very clearly new introductions that are in the process of expanding and increasing in density. Any new introduction has a few different models it could follow and you never know when things might get out of control (if the species finds appropriate habitat).

My millipede research is in desperate need of funding, by the way, so…that’s my plug. Study into new millipede introductions in tropical and subtropical United States has been sorely lacking since the death of Rowland Shelley in 2018 and new introductions have been spreading fast, something I have data for and want to study but have no ability to justify within my job since we have no assigned funds, currently.


Some isopods have really local distributions, Tommy Thomson park in Toronto has the only seemingly extant population of the European Androniscus dentiger, although there’s old reports from New York and Newfoundland that I can’t find specifics for.

Hawaii has a ton of really weird local introductions, including Nagurus sundaicus being introduced to Pearl and Hermes (a very remote atoll) and seemingly nowhere else somehow.

Florida probably has a ton of tiny introduced isopods that no one’s found yet, recently I was sent a photo of what’s probabaly the first Gabunillo in North America from FL, so if anyone in FL’s interested in finding first continental records you can dig around in urban areas to find some really weird stuff!


There’re many like this, e.g. Larerannis orthogrammaria which is out of its native Asia is now found on the North border of Moscow and Moscow Oblast.

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Black-tailed Prairie Dog is established in Wisconsin only immediately and around a safari park in Marquette County where they escaped from some time ago.

A crazy hybrid of two Spiny-tailed Iguana species is established in Arizona only in and around the Arizona-Sonora Desert Museum, a zoo and botanical garden a few miles west of Tucson.

As for areas that are a bit bigger, the Great Tit is found in North America only in and around the city of Sheboygan, Wisconsin. The Red Junglefowl has some large introduced populations in Florida, but outside of Florida the only introduced population in North America are found in a small rural town in Georgia and the grounds of a university in Texas.


Many animals (and sometimes plants), such as Green Anoles in Michigan, are found only in a single greenhouse.

Convict Cichlids, swordtails, and guppies are established in a hotspring inside Grand Teton National Park.

Mexican Gray Squirrels are established on the small Elliot Key off southern Florida.

Black-and-green Poison Dart Frogs are found in a small patch of rainforest on Oahu (and also Maui apparently).

Greater Rheas are found in a small area of Germany.

Brush-tailed Rock Wallabies are found on a small area of mountain slope on Oahu.

Red-necked Wallabies are found on a small island off of Ireland.

The UW-Madison Arboretum in Madison, WI is home to several introduced plant species found nowhere else in the state.

African Clawed Frogs are established in Arizona only on a single golf course on the north side of Tucson.

Ensatina are established in a small area in northern Arziona.

Sockeye Salmon are introduced in Wisconsin only on one small isolated lake in the northeast part of the state.

There’s a species of scorpion (forget which one) established on a few acres in England.

Common Hippos are established in a small area of Colombia.

Eastern Chipmunks are established in ard around the grounds of the Wuppertal Zoo in Germany, where they escaped from several years ago.

Green Iguanas are found in the Jurong area of Singapore, also originating from zoo escapees.

Common Wall Lizards are established in Cincinnati, Ohio, they were released in the 70s.

Green Monkeys are found in and around the Miami airport.

Patas Monkeys are established on a small island off the coast of Puerto Rico.

This is one of my favorite subjects.


Silver Pheasant is found in Canada only on a small area of Vancouver Island.

Indian Palm Squirrels are established on the grounds of Perth Zoo in Australia, another example of zoo escapees establishing populations.

There’s a small population of Stump-tailed Macaque introduced on an island in a lake in Mexico.

Black-tailed Jackrabbit is also established in Florida only in and around the Miami airport.

Giraffe Cichlid is found in a single lake in Utah.

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Northern Cardinal in the Whittier Narrows area of Los Angeles

Black-throated Magpie-Jay in the Tijuana River Valley in San Diego

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Small Balsam is within North America only found in and around Eau Claire, WI.

For how long? It’s so agressive, I don’t believe it can stay at one place without work to exterminate it. Oh, btw iNat has more valid observations in different parts of NA.

I wasn’t aware of it being anywhere else, but I suppose it might be. Regardless the Eau Claire population is the only one in Wisconsin. It’s only been there for a few years, it will probably spread into other areas sooner or later.

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Has anyone found any interesting species found introduced within a specific greenhouse? I found Teddy Bear Cholla spreading on their own inside the Desert Dome at the Omaha Zoo, making it a very small and local introduced population.

We have Himalayan mountain tahr on Table Mountain.
Thanks to a pair that escaped from Cecil John Rhodes private zoo.
Some years ago the tahr were culled so klipspringer could be reintroduced.

But a few tahr have evaded culling

And these are the locally indigenous klipspringer

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I’m worried about Kalopanax septemblobus. I think that species has high invasive potential and I strongly suspect that the only reason it is not more widespread is that it is so rarely planted. It seems to have escaped into the wild very commonly on the few sites where it has been planted. I saw it escaping around where it was planted in Cleveland, Ohio once.

Also, ecologically, it has a lot of factors that could give it potential to invade intact ecosystems, like it is shade-tolerant, and it tolerates a wide variety of conditions as long as the site is not too hot and dry, and it produces large quantities of fruits that are attractive to native birds, who help spread it. Furthermore, none of the closely-related species (Schefflerieae) are native to eastern North America (Oplopanax horridus is native to the northwest and that is the only one) which may make it hard for native insects to adapt to eat it.

I would urge arboretums to completely remove this species for this reason.

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So on the original topic here, with birds the classic example is the Eurasian tree sparrow, Passer montanus, which is established mainly around St. Louis and north for a short distance along the Mississippi river. It’s peculiar in that it got well-established there but has not spread much beyond there, unlike the House Sparrow which is not only common but often dominant in anthropogenic habitats, coast to coast.

With plants, there are tons of examples and if you look through species listings on BONAP you notice the disturbing pattern that many of them are established around the most famous arboretums, including St. Louis county, and many in the Philadelphia area, some around other cities. All of this points to the horticulture industry, especially the focus on growing “exotic” plants in gardens, being a major driving factor in the establishment of new invasive plant species, althogh it is certainly not the only factor, there are plenty of plants that became invasive that either were introduced as food plants, or just came as “weeds” by seeds hitching a ride somewhere.

Some examples of these, including the field maple Acer campestre, which is primarily established around the Philadelphia area but also has spotty introductions across the continent, including one in the bay area in CA even:

One that I also find kinda funny is the sweet potato:

It seems sorta weird to me that it has established a population in upstate NY! I didn’t realize it could survive in such a cold place. Most of its populations are where you’d expect, Louisiana mainly, where it is both warmer and widely cultivated.

Another plant example that I’ve been following is Cephalotaxus harringtonia, a slow-growing Asian conifer, in the area in and around the New York Botanical Garden. There are at least 65 plants in a 300 acre area per this study, all born from a single breeding pair at the NYBG. It is now in its second generation, as some of the seedling females are also setting crops. This plant takes at least 5 years to reach sexual maturity from seed, is dioecious, and it’s also marginally hardy in New York, but none of that has stopped it from spreading anyway. You can check the map here. @danielatha wrote the paper, and he’s been using iNaturalist to record his observations, which is very cool!