Top 10 Invasive Species Found in New Zealand

Updated: Aug 7, 2021

New Zealand has been known for having no natural predators. At least this was like that before the humans settled. It was populated by Polynesians around 700 years ago. Then it was colonized by Europeans who brought new culture, language, and social order.


With the Europeans came some of the nastiest pests. They were brought in the hopes to establish better trades. In this article, I will tell you more about these nastiest pests, what they are, and what damage they cause.


New Zealand Magpie

Australian magpies are robust birds, 37 to 43 cm in length. They are very sedentary and territorial. They can be very aggressive at protecting their nests and competing for food. Not every other native species can confront a magpie. That is why magpies are viewed as New Zealand's invasive species.


Over 1000 Australian magpies were introduced into New Zealand from 1864 to 1874. They are treated as pest species by many regional and local councils. They are thought to displace other native species of New Zealand.


A Magpie
A Magpie

Rats

Rats are known for their destructive eating habits throughout the world. In New Zealand, it is no exception. The so-called Ship rats and Norway rats are two major pests that were introduced by Europeans. The other species is called Kiore. It is known for having a cultural and spiritual significance to Maori people.


All three species pose a threat to native plants, bird eggs, flowers, birds, seeds, lizards, and frogs. Their eating habits make them strong competitors in finding and securing food sources. Rats are good climbers and can climb up a tree to prey on nests. They also eat large flightless invertebrates such as snails and weta.


The image displays the following rats in sequence from left to right: the Ship rat, Norway rat, and Kiore rat.


Argentine Ants

Argentine ants pose a serious threat to New Zealand's biodiversity. They are found in urban and natural areas.

Ants are very aggressive and territorial. Their unique attribute is the ability to cooperate. They can connect many colonies forming a huge network of ant workers. Their increased appetite makes them even more dangerous to local trees, flowers, and plants.


They are also major household and garden pests, usually found in warm, dry soil. They kill native invertebrates that otherwise would feed native species. They can threaten endangered populations by eating lizards, bird eggs, and hatched chicks. During Spring and Summer, they prefer to feed on nectar and honeydew.


Because of their diverse diet, they displace indigenous populations of Kiwi. They also compete with nectar-eating birds such as Tui and Bellbirds. They also tend to eat lizards, skinks and geckos, and other native invertebrates.




Possum

The common brushtail possum is the greatest threat to New Zealand's natural environment. Its size and teeth make it one of the most destructive pests in New Zealand. It was introduced from Australia in 1837 to establish a fur trade. The first release was unsuccessful. But the second release, which was made in 1857, 20 years after, was successful.


The threat posed by possums is their omnivorous and herbivorous diet. They tend to eat carrion, bark, crops, eggs, plants, leaves, and everything of nature origin. Their only predator - the feral cat, is much smaller in size so it does not hunt down possums in large enough numbers to guarantee good control measures for possum population size.


The plenty of food that possums can eat in New Zealand makes them reproduce very fast. As of today, around 30 million possums are inhibiting the native lands of New Zealand. This has massive implications on native flora and fauna.


Besides the mentioned destructive dietary habits, possums are also carriers of several diseases. Most problematic of which is Bovine Tuberculosis. BV, for short, affects cattle and causes trouble to farmers.


Feral Cat

A feral cat looks like an ordinary one except it lives in the wild. It also does not rely on humans for the provision of food and shelter. In contrast to stray cats, wildlife feral cats are completely separated from humans. They have their needs provided by themselves.


European explorers brought the first cats to New Zealand in 1769. Those cats helped control the number of rats aboard more than 50 years after cats were introduced to New Zealand. A feral cat population was established and was expanding around the country.


Feral cats have a major impact on native and non-native species. They are considered invasive predators. They prey on birds, rabbits, bats, lizards, mice, and insects.


Feral cats prefer to live near coastal areas and riverbeds. This makes their predation impact skink populations in these places.


On offshore islands, cats feed on forest and sea birds, which has major consequences as well.


Their habitats usually consist of forest areas, farmland, riverbeds, and coastal areas. So if you go out for a bushwalk, be prepared to meet a feral cat in the wild!


Rabbits

Rabbits are a significant agricultural and economical threat. European rabbits were among the first mammalian animals introduced to New Zealand. They were distributed throughout drier regions of the mainland and many offshore islands. They populate those environments at an extreme pace resulting in large numbers of them.


Domestic rabbits were carried on sailing ships as potential food. They were imported in the 1860s to establish the domestic fur and meat trade. Increased farming, later on, assisted their growth in numbers. By the 1880s rabbits became a serious threat to the fragile New Zealand economy.


Rabbits are agricultural pests. They compete with livestock for pasture, consuming the grass and vegetation on land. They also destroy native plants and flowers by browsing.



Invasive Plants

Seaweed Undaria
Seaweed Undaria

There are many plants unique to New Zealand such as tree ferns, kauri, pohutukawa tree, and Kauri tree. There are also introduced species that include pest plants as well. Weeds are the most common pest plants in New Zealand:

  • Seaweed Undaria, which is a threat to Fiordland's marine environments,

  • Carnivorous weeds in Auckland such as Cape sundew and bladderwort. They are two invasive plants introduced from South Africa. They wreak havoc on New Zealand’s native vegetation.

  • Freshwater weeds. These are African oxygen weed Lagarosiphon major, alligator weed Alternanthera Philoxeroides and clasped pondweed Potamogeton Perfoliatus. These weeds pose a threat to the native freshwater plants as they degrade the quality of New Zealand’s wetlands.

  • There is also golden dodder, which is a threat to Waikato wetlands and lakes. It damages flora and fauna on Matiu/Somes Island in Wellington Harbour and Wilding conifers. These are invasive weeds that are in danger of altering the unique landscapes of New Zealand.


Stoats, Weasels, and Ferrets

Both stoats, weasels, and ferrets are members of the mustelid family. They are considered New Zealand's largest pest animals. They were introduced to New Zealand as early as 1879 to control rabbits that damage pastures. They cause harm to the natural world of New Zealand.


Stoats

The stoat is an enemy for New Zealand's native birds as it hunts them down in large numbers. They live and prey in any habitat as long as there is a food supply. They can be found on beaches and in the countryside, forests, scrub, dunes, and farm pastures.


Stoats are dexterous climbers and hunt during the day as well as at night. They are agile swimmers.

A stoat
A stoat


Weasels

Weasels are found in low numbers in most habitats around New Zealand. It poses a threat to New Zealand's ecosystem. Farmers introduced them in the mid-1870s to control the number of rabbits. Despite the protests of bird experts, weasels, stoats, and ferrets, were released into the pasture. Soon after they populated the forests west of Lake Manapouri.


Like stoats and ferrets, weasels prey on native birds, their eggs, lizards, and insects.

A weasle
A weasle


Ferrets

Although ferrets hunt for rabbits, they also prey on and kill other native species. They pose a threat to wildlife. They were introduced with stoats and weasels in the 1880s to control rabbit populations but became a nuisance to the ecological environment. They tend to breed fast and kill birds like Kiwi, weka, blue duck, and kakapo - a large, flightless, nocturnal, ground-dwelling parrot.

A Ferret
A Ferret

Stoats, weasels, and ferrets are the only mustelids present in New Zealand. Apart from them, there are also minks and otters of the same mustelid family. But they live in other countries.


Other Pests

Despite mentioning the most obvious pests, some unobvious pests impact New Zealand's flora too. These are:

  • Wild deer. It damages forests by feeding on native plants, trees, and seedlings. This causes a restructuring of the composition of plants in the forest. This also leaves many animals without food and shelter.

  • Feral goats destroy vegetation and damage the forests.

  • Wasps that consume massive amounts of honeydew.


Control Methods

The primary organization responsible for pest control in New Zealand is the Department of Conservation (DOC). It organizes events and programs on the eradication of serious pests in New Zealand. These programs involve distributing poison throughout the pest's living areas, applying bait and traps, and providing a reward for mass shooting and killing of the most dangerous pests.


The DOC organization is also responsible for maintaining reservations throughout New Zealand. They do it by keeping them enclosed in fences and not allowing pests to leak in on reservation entry points.


Final Thought

New Zealand has been known as a predator-free land for many years until European colonization brought their species. Many New Zealand predators are now considered pests since they prey on indigenous plants and animals. Many of them are not an integral part of New Zealand fauna. The Department of Conservation handles the reduction of the number of such pests in New Zealand. It tries to mitigate the risks of their impact on the ecological and agricultural sectors of New Zealand's industry.


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