6 Unusual Invasive Species Around the World

Read on to learn about 6 species that are invasive in parts of the world.

Aug 25, 2023By Michael C., BA Fisheries and Wildlife
unusual invasive species

As humans have spread throughout the world, various other animal species are also taken along, whether accidentally or intentionally. Many species, such as feral hogs, rats, and cats, are notorious for their catastrophic effects on ecosystems worldwide. However, some invasive species around the world may be a shocker to many. Read on to learn more!

1. Gemsbok – New Mexico

gemsbok standing in scrubland
Image credit: Sharp Photography/Wikimedia Commons

The gemsbok is a large oryx that is native to the arid, dry savannas and deserts of Southwestern Africa. In 1969, the New Mexico State Department of Game and Fish introduced gemsbok throughout the Tularosa basin for hunting purposes along with a few other large game species. Considering that New Mexico is very similar in climate to its native range in Africa, this species has flourished, especially in the absence of predators. Coyotes and cougars, unlike lions and hyenas, are ill-suited to take down gemsbok, and therefore oryxes can thrive and reproduce without any problems.

As their numbers increase in the thousands, conservationists fear that the gemsbok could compete with native ungulates, such as pronghorn and mule deer. There are also fears of disease transfer. Livestock ranchers view the gemsbok as a pest, competing with cattle for forage. Currently, New Mexico’s gemsbok population is being controlled through hunting programs, and some hunting charters even sell licenses to permit the hunting of the antelopes.

2. Jackson’s Chameleon – Hawaii

chameleon on stick
Image credit: Martin J. Whiting

Back in the 1970s, a shipment of Jackson's chameleons was imported on the island of Oahu to be destined for the pet trade. Having been distressed by the rough conditions during transport, a pet store owner decided to let these unique lizards outside for fresh air. From this, some of the animals escaped, and since then, the chameleons have spread throughout the island. Populations of feral chameleons have also been reported in nearby islands, such as Maui and Hawaii.

Hawaii is home to many endangered invertebrate species, from insects to snails. A study conducted in 2009 has shown that the critically endangered tree snail, Achatinella mustelina, has been discovered in the guts of chameleons. Control efforts are underway to ensure that these reptiles don't cause further ecological damage in Hawaii’s fragile ecosystems.

3. Greater Rhea – Germany

rhea in foliage
Image credit: Michael Plaster/eBird

Distantly related to the ostrich, the Greater rhea is a large, flightless bird native to the pampas and grassland regions throughout the South American continent. This bird, however, can also be found in grassy meadows and fields around Northern Germany. Back in the 1990s, a small flock of rheas escaped from a small zoo, and since then the population has exploded to around 500 individuals.

Fortunately, rheas have very little ecological impact in areas where they’re found, and they were even protected by law at one point. However, they’ve become a major agricultural pest, causing considerable crop damage. Egg manipulation by drilling or using paraffin wax to suffocate developing embryos inside is one method used, but more recent efforts have focused on hunting adult birds.

4. Red-Necked Wallaby – UK and New Zealand

wallaby mother with joey in zoo
Image credit: Tierpark Stadt Haag

Wallabies, including the Red-necked wallaby, have been introduced into a few countries outside their native land of Australia, including Ireland, Great Britain, and New Zealand. In New Zealand, five species, including the red-necked wallaby, have been brought over both intentionally and accidentally. Some were released for hunting purposes, while others have escaped from private zoos (as in the case of the United Kingdom).

Wallabies have no predators in either country, allowing them to flourish and populate with ease. In the case of New Zealand, these marsupials feed on native plants, altering and even destroying forests as they feed on the underbrush. This, in turn, displaces native species and alters habitat composition. They also have a major impact on agriculture, destroying crops and competing with livestock. Fortunately, the New Zealand government is working proactively to control the invasive wallaby population through hunting.

In Britain, wallabies don’t pose as much of an ecological impact as plant communities are more adapted for grazing herbivores, though control efforts are underway.

5. Reindeer – South Georgia Island

reindeer and penguins in snowy environment
Image credit: Brian Gratwicke/Flickr

Located over a thousand miles away from the South American continent, the island of South Georgia is almost inhospitable due to its subarctic temperatures and unforgiving environment. Yet, a Norwegian commercial whaling operation was established on the island in the late 1800s despite these treacherous perils. Along with the whalers came the reindeer, which were introduced on the island for food and hunting purposes.

When humans left the island, the reindeer were left behind, allowing them to breed uncontrollably. Even through harsh conditions, the reindeer thrived as the environmental conditions of their native Scandinavian homes were vastly like those of South Georgia Island. A few heads of animals became thousands, and from this, they have impacted the island's ecosystems negatively. A lot of the island’s native plants have been decimated, in turn altering soil quality and displacing habitats for various native bird species.

Eventually, thanks to an organized collaboration by Sami reindeer herders, hunters, and researchers, most of the invasive reindeer population has been eradicated. As of 2017, only a few animals have been spotted.

6. Hippopotamus – Colombia

hippo yawning in water
Image credit: Bernard Gagnon/Wikimedia Commons

Hippos are iconic animals, and it may be surprising to some that these beasts are invasive in Colombia. The hippopotamus is the world’s largest invasive species, and how they got there is rather interesting. The notorious drug lord Pablo Escobar owned a private zoo on his massive property back in the 1970s, keeping exotic animals of all kinds. After Escobar’s death, all of the animals were moved out except for the hippos. The four hippos were left to stay as they were deemed too dangerous to relocate, and they eventually escaped to the nearby Magdalena River.

Eventually, their population exploded, and as of 2019, there are around 90-120 hippopotamuses living in the Magdalena River Basin. As they eat copious amounts of native vegetation, the hippos can potentially displace suitable habitats for many native species, such as otters, turtles, and caimans. An important study published in 2020 revealed that lakes populated with hippos contained higher amounts of cyanobacteria, which can create toxic algal blooms.

Hippos also pose a danger to local communities, as attacks have been reported among fishermen and farmers. There is a management plan being created to control hippos, mainly through chemical sterilization.

Michael C.
By Michael C.BA Fisheries and Wildlife

Michael holds a BS degree in Fisheries and Wildlife from Michigan State University. He formerly worked at a pet store as an animal care associate and is the former president of the MSU Herpetological Society. Michael currently owns three snakes (a corn snake, a Kenyan sand boa, and a checkered garter snake) and a leopard gecko. Interests include almost anything animal-related. Michael enjoys drawing, gaming, and having fun in his free time.