‘This is a tragedy’: swimming snakes open new front in battle with Balearic lizards The horseshoe whip snake, introduced to Ibiza two decades ago, has become an existential threat to the native Ibiza wall lizard, with populations dwindling rapidly on many islets. The snakes’ ability to swim has allowed them to colonize new territories, leading to the extinction of unique lizard lineages on 10 islets. While captive breeding programs and culling efforts are underway, the situation remains dire, with researchers likening it to ecological disasters like the introduction of the brown tree snake to Guam.

• The horseshoe whip snake, an invasive species, has become a major threat to the Ibiza wall lizard.
• Snakes have been observed swimming to nearby islets, leading to the extinction of unique lizard populations on 10 islands.
• The lizards are a keystone species, controlling insect populations, pollinating flowers, and dispersing seeds.
• Invasive snakes were likely introduced through imported ancient olive trees and have spread rapidly across Ibiza.
• More than 3,500 invasive snakes were captured on Ibiza last year, and over 16,000 culled since 2016.
• Despite conservation efforts, including captive breeding programs, the future of many lizard populations is uncertain.
• Ironically, some urban areas of Ibiza have stable lizard populations because snakes are run over or killed by humans.