5 Islands Where Invasive Snakes Caused Local Wildlife to Go Extinct

Written by Emmanuel Kingsley
Updated: December 31, 2022
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The ecosystem is an important natural system that supports life as we know it. While humans are now conversant with this fact, we weren’t always, allowing us continually make costly mistakes over extended periods. Consequently, many states, islands, countries, and even continents have reported losses of plant and animal species due to human intervention.

However, islands seem to be getting the worst of it, and there’s a perfectly good explanation for this. This article explores 5 islands where invasive snakes caused local wildlife to go extinct. If you’d also like to find out why islands are home to almost 40 percent of all critically endangered animals on record, this article has all you need to know.

Why Are Islands More Susceptible To Invasive Species?

An island is best defined as a piece of land surrounded by water. Consequently, it has limited resources such as territory, food, prey, and predators. As a result, many native island animals have evolved to feed on a small diet. Animals like these are called specialist species. Other species have also developed new survival skills, thanks to evolution. One such example is the marine iguana found on the Galapagos islands. These reptiles are known to dive into the water to look for food.

Due to islands’ limited resources and native/specialist species, they have remarkably fragile ecosystems. If, for example, a new species with a similar diet to any native specialist species enters the island, problems could ensue, especially if the island has no predators for this new species. Not only would there be less food and more competition for the native species, but the prey in question would be overhunted. This means that the native species and the prey are at risk of extinction.

On the other hand, most invasive species are generalists instead of specialists and simply move on to another species once they have hunted one into extinction. They do this until they hunt the entire island into extinction. Sadly, this happens pretty frequently. Research has shown that invasive species are the primary cause of the extinction of wildlife on islands. In fact, research has also shown that invasive species are responsible for about 42 percent of all threatened or endangered species.

This is a huge problem as many species found on islands aren’t seen anywhere else in the world. About 1189 highly threatened vertebrate species are situated on 1288 islands worldwide. This means that once an animal goes extinct on these islands, they are lost forever with all the knowledge that could be gained from studying them. You might wonder how these invasive species get onto islands, but it’s really straightforward; humans are largely responsible. So many animals that have now transformed into invasive species would never have been able to get to their new habitats without humans.  

5 Islands Where Invasive Snakes Caused Local Wildlife To Go Extinct

Ibiza, Guam, Mallorca, Canary, and Formentera Islands are 5 islands where invasive snake species caused local wildlife to go extinct.


Ibiza Island

Horseshoe whip snakes prey on Ibiza’s native wall lizards.


Ibiza is gaining popularity again, but not for great reasons. Horseshoe whip snakes have begun to wreak havoc on the population of Ibiza wall lizards, the last remaining endemic vertebrate on Ibiza. We know that these colubrid snakes are responsible for the population decline of these lizards because studies prove that Ibiza wall lizards make up at least 56 percent of their diet.

Earlier research showed that the snake entered Ibiza by hitching rides on ornamental olive plants transported to the island from other territories in the Iberian Peninsula. These snakes now inhabit up to 49.31 percent of the island, which encompasses about 43.04 percent of Ibiza wall lizards’ territory.



Brown tree snakes are responsible for eradicating two of Guam’s three native bat species as well as over half of its native bird species.


Guam is the largest island of the Mariana Islands and is located in its southernmost parts. The island currently has about 4 invasive animal species, with the brown tree snake causing the most devastating effects. According to the Invasive Species Compendium, it is responsible for eradicating two of Guam’s three native bat species as well as over half of its native bird and lizard species.

These snakes are extremely agile climbers and swift movers, causing them to remove native pollinators, which results in the decline of native plant species. Ecologists have also discovered that Guam has almost 40% more spiders than its surrounding islands because of the eradicated birds that would usually feed on them.

Mallorca Island

Mallorca Island

False smooth snakes are invasive on Mallorca Island and prey on the island’s native Lilford’s wall lizard.

©iStock.com/Balate Dorin

Mallorca is the largest of the Balearic Islands, an archipelago in Spanish territory. This territory was invaded by false smooth snakes, colubrid snakes that are now a relatively common sight in Mallorca. False smooth snakes were introduced in historic or prehistoric periods. Since quite some time has passed since their invasion, they are now commonly spotted despite how dangerous they are to Mallorca’s ecosystem. 

The species is believed to be responsible for the extinction of Lilford’s wall lizard, a lizard native to the Balearic Islands. Sadly, these are not the only invasive species as exotic pets that escape their owners also end up in the wild. These species end up spreading and ultimately become a threat to the ecosystem.

Canary Islands

Canary Islands

The California king snake preys on three major native reptiles on the Canary Islands.


The Canary Islands is a popular archipelago in Spanish territory off the coast of northwestern Africa. The California king snake was introduced onto Gran Canaria in 1998 and by 2009 had become a major problem. Despite efforts from the Canary Islands Government to stop their growth, the species has continued to expand.

A survey showed that this snake has had devastating effects on three reptiles native to the Canary Islands; the Gran Canaria skink, Boettger’s gecko, and the giant lizard of Gran Canaria. Two of these species are important parts of plant reproduction and dispersal, and all three species help keep the populations of certain invertebrates in check.

Formentera Island

Formentera Island

Ladder snakes are invasive in Formentera and are responsible for the decline in Ibiza wall lizard populations.


Formentera Island is the smallest of all islands in the Balearic archipelago. The island is known for its beautiful waters and is one of the top tourist hotspots. However, despite its beauty, the island of Formentera battles with ladder snakes, an invasive species threatening the populations of some of its native species.

It preys chiefly on the island’s native Ibiza wall lizard, as research revealed that these lizards make up to 40 percent of the ladder snake’s diet. They are regarded as an invasive species by the island government and many other surrounding island governments.

Final Thoughts

Invasive snakes are a major problem which is why other islands like Hawaii are already taking measures to eradicate their 7 invasive snake species before the fragile balance of their ecosystem is damaged. This is why it is important to carefully consider the long-term feasibility of owning a pet before purchasing one. While letting it out into the wild might solve a minor problem for you, it definitely causes a larger one in the long run.

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The photo featured at the top of this post is © mapman/Shutterstock.com

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