Else Beekman
The giant lizard of Gran Canaria and the lizard of the Pityusic Islands (including Ibiza and Formentera) are facing severe threats from invasive snake species. The situation has become so dire that the International Union for Conservation of Nature (IUCN) has announced an update to the Red List, now classifying these reptile species as endangered.
These unique lizards are under threat from two invasive snake species. These snakes, which arrived on the Spanish islands about 25 years ago, are relentless predators. Today, the IUCN announced that the giant lizard of Gran Canaria is now critically endangered. Meanwhile the Canary Island lizard is classified as endangered. Both species have lost half of their populations since 2014. Similarly, the lizard of the Pityusic Islands has declined at the same rate since 2010. It is now also considered endangered.
Origins of the threat
The first invasive snake to decimate island species is the California kingsnake (Lampropeltis californiae). Native to the United States and northern Mexico, this snake was first captured in the wild on Gran Canaria in 1998, likely having escaped or been released as a pet. By 2007, the species was considered established on the island.
In the Balearic Islands, the greatest threat is the horseshoe whip snake (Hemorrhois hippocrepis), which was accidentally introduced. This predator arrived hidden among the root balls or trunks of large olive trees, popular for garden decoration. The first specimen was discovered on Ibiza in 2003, marking the start of a silent invasion that has led to the current disastrous situation.
Impact on local ecosystems
Elba Montes, an expert in biological invasions with the Herpetological Association, has studied the expansion of the horseshoe whip snake and its impact on lizards in Ibiza. Her findings, submitted to the IUCN, predict that by 2028, the horseshoe whip snake could colonise the entire island, likely leading to the extinction of the lizard. Local governments, such as Santa Eulària des Riu, are creating urban refuges for the lizards to support their habitats.
The disappearance of these lizards is not just an anecdote; it has far-reaching consequences for the ecosystem. Oriol Lapiedra from the CREAF research centre at the Autonomous University of Barcelona explained in El País that the presence of the snake leads to local extinctions of the lizard, altering the ecosystem. For instance, insect populations increase as their primary predator disappears. Moreover, lizards play a crucial role in pollination and seed dispersal.
Possible solutions
Lapiedra states that there is no magical solution to this problem. Although the invasive snakes have abundant food now, this will eventually decline, but by then, it will be too late for the lizards. A potential plan could involve breeding the endangered lizards in captivity.
On Gran Canaria, campaigns are underway to capture and reduce the population of invasive snakes. Since 2007, 18,356 California kingsnakes have been captured, with 2,389 caught in 2023 alone. Last year, 2,007 invasive snakes were captured on Ibiza. Preventive measures are crucial to avoid these situations, as native animals often suffer the most.
Despite the bleak outlook for many reptile species, there are success stories. The giant lizard of La Gomera has improved from critically endangered to endangered status thanks to breeding and reintroduction programs.
Also see: Invasive California kingsnake in Gran Canaria is advancing on the city