In addition to being one of the great European tourist destinations, the Pitiusas Islands have a unique jewel of nature: the pitiusa lizarda unique reptile in the world that only lives there. By living in isolation, the lizard populations on each islet have evolved independently, giving rise to 28 different subspecies.
This biological jewel today has a direct and truly terrifying threat: the horseshoe snake, a foreign species that was accidentally introduced to Ibiza in 2003, probably through ornamental olive trees imported from the Iberian Peninsula. Or so they thought: spotting a horseshoe snake is no longer something occasional, but they can even be seen swimming in the open sea. Spoiler: they are terrestrial snakes.
what’s happening. The Center for Ecological Research and Forest Applications (CREAF) has published an academic article that covers the origin and invasion status of the horseshoe snake. The expansion map is conclusive: in 2010 the snake was present in less than 5% of the Ibizan territory, in 2016 it already occupied 40% of the island and in 2025 it had reached 90%. As stated by the research team led by Guillem Casbas and researcher Oriol Lapiedra, when it conquers a new area, it can take less than three years to eradicate the entire population of lizards. The speed of expansion is unprecedented among invasive snakes in Europe.
What has never been seen is also the most disturbing: they have documented how snakes swim between islets, that is, they carry out active colonization. In 2024 they recorded a snake crossing 430 meters of open sea to the islet of Santa Eulària. The same sea that has served over the years as a barrier to the evolutionary isolation of the pitiusa lizard is no longer enough to protect it from its predator.
The unstoppable advance of the horseshoe snake. Ecology
Why is it important. The extinction of a species is always bad news from the point of view of fauna diversity, but this one is unique: its goodbye means that a unique and irrecoverable evolutionary lineage disappears, and according to the IUCN It is already cataloged as threatened, which means that population models predict a severe and continued reduction in the short and medium term. Beyond taxonomy, this eventual extinction would have its effect within an ecosystem as particular as the island and its balance, which could end with more extinctions due to a domino effect. In the case of the pitiusa lizard, it has pollinating and seed dispersal functions and if it does not do so, it puts the reproductive success of plants in check.
On the other hand, and although its importance is more relative, the Pitiusas lizard is one of the great cultural and identity icons for those who are from Ibiza and Formentera: this amphibian is deeply rooted in the collective local imagination and popular mythology.
Context. The magnitude of the problem is best understood within the biology of the islands. Islands are especially vulnerable ecosystems to invasive species because the loss of a single species can trigger cascading effects throughout the entire biological community. Invasive species enter the islands like an elephant enters a china shop: they compete for resources (more limited), alter habitats (smaller) and disturb ecological processes.
The Pitiusas lizard is a critical node for the islands: however, was For millions of years it was the only terrestrial vertebrate in the archipelago and did not develop anti-predatory behaviors against snakes. A parallel case studied in depth is that of the brown tree snake on the island of Guamwhich decimated native bird and lizard populations, causing an increase in insects and altering forest dynamics.
tragic consequences. The immediate ecological consequences are severe and quantifiable: there have already been local extinctions of lizards on at least 10 islets, and the snake has colonized between 12 and 15 of them through active swimming. And unfortunately, it’s just the beginning: this global study highlights that the impact of invasive vertebrate species on seed dispersal in island ecosystems is even greater than that caused by the extinctions of native fauna. Or what is the same, there may be a disruption in the plant regeneration of these islets. Likewise, its disappearance can take its toll on agriculture indirectly, as the lizard regulates the insect population.
Is there a solution? The most urgent and important shock measure is to actively control the snake invasion. In 2025 the Balearic Government surpassed the 4,400 captures of invasive snakes in the Pitiusas and has already opted to leave the traps throughout the year. In 2026 the device will continue to expand with more resources. Of course, with a presence of 90% already in Ibiza, total eradication is unfeasible in the short term: the most realistic thing is to contain the advance and protect refuges.
On the other hand, the conservation of the pitiusa lizard is also a priority objective, with several breeding lines of pitiusa lizards with genetic criteria in collaboration with the Barcelona Zoo. In the long term, the only structural solution is to combine the control of the snake with the conservation of the lizard’s genetics for a later reintroduction into its territory.
Cover | Albert Masats and Swimming Snakes Wipe out Endemic Lizards from Mediterranean Islets, Oriol Lapiedra
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