By John Kerr 14/06/2017

New Zealand conservation researchers have assembled a rogues’ gallery of the worst invasive species for islands around the world.

In a new article in Environmental Conservation, published this week, Dr James Russel from the University of Auckland and colleagues review the challenges of holding invaders at bay on small island states.

Invasive species can have a detrimental impact on biodiversity, write the authors, but also wreak havoc with agriculture, health, tourism and the economy.

“Islands such as New Zealand have long been known to be vulnerable to the impact of invasive species introduced to them, the classic example being the introduction of mammalian predators driving many bird species to extinction,” said Dr Russell in a media release.

“However, although every island in the world fights its own battles against invasive species, this study provides a global overview of trends in the impact and distribution of invasive species across all islands for the first time.”

Read more about the research on

Island nations’ top invaders

The authors canvased the extent of species invasions across small-island developing states, covering a total of 33 self-governing, wholly island nations around the world. Data was drawn from the Global Register of Introduced and Invasive Species (GRIIS), a massive database of expert-verified invasive species detections.

Outlined in the paper, the top 15 list of invasive alien species on islands includes some expected classics like mice and rats but also a number of plants that do not have the same infamy in the public eye:

island invaders
Alien invaders, from top: house mouse, tilapia, purslane and ghost ants. Credit: public domain; Greg Hume; ZooFari; Sarefo /wikimedia.

White leadtree


Longhorn crazy ant

Black rat

Red bead tree

Common guava

Quick stick

Air plant

Ghost ant

Southern house mosquito

Little ironweed

Barbados nut

House mouse



Managing island invaders

When it comes to battling incursions the best offence is a good defence, say the authors; prevention of biological invasions in the first place is by far the most cost-effective management strategy. Effective quarantine, surveillance and response biosecurity efforts can prevent invasive species gaining a foothold on small islands. Failing that, control of the species – keeping population numbers down and limiting its spread – is needed to keep it in check and protect native flora and fauna. This will make any future eradications efforts much easier.

Eradication of invasive species on islands is possible, and the authors highlight a large number of successful eradication efforts worldwide.

From the Database of Island Invasive Species Eradications (DIISE), over 1200 eradication attempts have been made on over 800 islands worldwide, with a success rate of c. 85%. The majority of these eradication attempts (60%) have been in the Pacific Ocean (with half of these being in New Zealand).

Study co-author Dr Nick Holmes from the Island Conservation NGO says invasive species are a key threat to plant, animal and human communities dependent on islands.

“But there is hope. There are many examples of invasive species prevention, control and eradication leading to positive conservation outcomes. We should strive to replicate these successes, and improve our knowledge of how to tackle bigger challenges on islands across the globe.”