Horseshoe Snakes Devour Ibiza's Unique Lizards

The horseshoe whip snake, an invasive species originating from mainland Spain, poses an existential threat to the unique Ibiza wall lizard. Researchers confirmed this threat in April 2024 with video evidence of a snake swimming to Santa Eulària islet, a new territory for the insatiable predator. This follows suspicions from local experts and anecdotal reports from fishermen and tourists.

Introduced to Ibiza about two decades ago, the snakes have rapidly spread, now present on at least 90% of the island. Their colonization is partly facilitated by the import of ancient olive trees, which provide transport for hibernating snakes and eggs. The Ibiza wall lizard, once abundant and culturally significant, has been drastically reduced, with its conservation status elevated to 'endangered' by the IUCN in October 2022.

This ecological imbalance has dire consequences. The lizards are a keystone species, controlling insect populations and aiding in pollination and seed dispersal. Their extinction on 10 islets, including Santa Eulària where populations dropped from 72 in 2016 to just three in 2023, represents a loss of unique evolutionary lineages. Predictions suggest snakes will inhabit 100% of the island by the end of 2027.

Efforts to combat the invasion include capturing and culling over 3,500 snakes last year and more than 16,000 since 2016. A captive breeding program for lizards has also been initiated. Despite these measures, the outlook remains grim, with researchers drawing parallels to the devastating impact of the brown tree snake on Guam's native bird populations.