Invasive horse snakes are swimming between islands around Ibiza, posing a significant threat to the region's native wildlife [1].
This biological invasion is critical because the snakes target endemic species that exist nowhere else on Earth. The spread of these predators disrupts the fragile ecological balance of the Balearic Islands, potentially leading to the extinction of local fauna.
The horse snake, known as the couleuvre fer-à-cheval, was introduced to the area approximately 20 years ago [2]. While many snake species are terrestrial, this particular population has demonstrated the ability to navigate the sea to expand its territory [1].
Researchers have documented 14 confirmed observations of these snakes swimming over a 10-year period [3]. These reptiles are formidable predators that can exceed two meters in length [3]. Their mobility allows them to move between islands, bypassing natural geographic barriers that previously protected native species [1].
The primary victim of this invasion is the Pityus lizard, a species endemic to the islands [2]. The snakes predate on these lizards and outcompete other native fauna for resources [1]. This predation creates a cascading effect on the local food web, threatening the overall biodiversity of the archipelago [1].
Local concerns have grown as the snakes become more visible to both scientists and tourists [4]. The ability of a large predator to cross open water means that no island in the chain is entirely safe from colonization [1].
“The horse snake was introduced to the area approximately 20 years ago.”
The presence of swimming invasive predators in the Balearic Islands highlights the vulnerability of island ecosystems to non-native species. Because endemic species like the Pityus lizard evolved without these specific predators, they lack the natural defenses to survive a sudden population surge of horse snakes. This situation underscores the difficulty of containing invasive species once they acquire the ability to bypass marine barriers.
