Can Ibiza's colorful lizards survive a snake explosion?

Guillem Casbas has a favorite spot to eat lunch on the Spanish island of Ibiza: a stone bench shadowed by an olive tree on a cliff overlooking the sea, with the neighboring island Formentera visible in the distance. Ibiza wall lizards—green on top, blue on the sides, white on the belly, and a little under three inches long—often visit him there. He enjoys giving them pieces of tomato from his sandwiches.

“I call them friends,” says Casbas, a herpetologist and doctoral student at CREAF, Spain’s Center for Ecological Research and Forestry Applications. “They are super, super friendly, innocent, and cheerful.”

The Ibiza wall lizard has long fascinated scientists because isolated populations of the species evolved markedly different colorations. While Casbas’ “friends” are green and blue, others are baby blue with orange on the belly. Some are all black. Dozens of small islets surrounding Ibiza and Formentera are each home to distinct-looking lizard groups—with greens, blues, indigos, and shimmery coppers represented in over two dozen different patterns.

It’s rare for a single species to have such a dazzling array of colors and patterns, particularly among vertebrates. How these lizards became so kaleidoscopically diverse is a longstanding scientific mystery.

“Within the small region, you find so many very, very distinct types of coloration—I think that makes them really special,” says Nathalie Feiner, an evolutionary biologist who works on the genomic analysis of the lizards at the Max Planck Institute for Evolutionary Biology in Germany.

Tragically, she says, this diversity may soon disappear. Six years ago, Casbas would take breaks further inland, where the lizards abounded by a mountain spring. Since then, an invasive predator called the horseshoe whip snake expanded into that area and there are no lizards in that spot anymore. “This was shocking for me,” Casbas says. In fact, some of the nearby islets have entirely lost their lizard populations to the snakes, too.

The lizards aren’t just aesthetically pleasing reptiles sniffing out food from human sunbathers. As pollinators, insect-eaters, and seed dispersers, Ibiza wall lizards are considered a keystone species, critical to their island ecosystems.

Scientists are in now a race against time to document the diversity of surviving lizard populations, and come up with solutions for safeguarding the species against the increasing snake threat. A 2021 analysis in Current Zoology found that Ibiza wall lizards could go extinct on their namesake island within a decade, as well as on many surrounding islets.  “We are witnessing the extinction of a species’ life—and not only a species, but probably one of the most striking cases of color biodiversity on Earth,” says Roberto García-Roa, an evolutionary biologist and photographer who also studies the lizards at the University of Valencia, Spain.

Longtime island residents

Ibiza wall lizards got their species name Podarcis pitysensis from the Pityusic Islands, a subset of the Balearic Islands, which is an autonomous community off the eastern coast of Spain. Ibiza, the largest of the Pityuses, is slightly smaller than the combined areas of Brooklyn and Queens, and widely known for its nightclub and beach scenes. Locally, the wall lizards are a kind of mascot. “They really are a cultural icon for these islands,” says Oriol Lapiedra, a biologist who runs a behavior and evolution laboratory at CREAF, and a National Geographic Explorer. Shops catering to tourists sell fridge magnets, coin purses, beach towels, and earrings that all pay homage to the colorful lizards.

But long before the first DJ started spinning electronic beats in Ibiza Town, lizards have inhabited these islands. Biologists believe the Ibiza wall lizard split off from its sister species, Lilford’s wall lizard (Podarcis lilfordi)—which today survives only on small islands near Mallorca and Menorca, to the east of Ibiza—over 2 million years ago, when it began its evolutionary journey to a kaleidoscope of color.

During the last several hundred thousand years, multiple cycles of rising and falling seas formed land bridges to merge some of the Balearic Islands and at other times, split land masses apart. These changes would have, in turn, connected and then isolated various wall lizard groups, and impacted the diversity of their appearances over time.

“You have this very complicated evolutionary history where sometimes they're in contact, sometimes they're isolated,” says Tobias Uller, evolutionary biologist at the University of Lund in Sweden and National Geographic Explorer. He hopes his team’s research into the lizards’ genetics will reveal clues as to when and why their different physical appearances emerged. “We're trying to understand where that extraordinary capacity for generating diversity and novelty comes from.”

Spanish herpetologist Eduardo Boscá formally described the Ibiza wall lizard in 1883, and in the 1920s and 30s, collectors captured Ibiza wall lizards for museums or for pet sales. Catalogs from Berlin pet seller Scholze & Pötschke in the early 1930s advertised over a dozen subspecies, according reports in the online lizard magazine L@certidae.

Both species of wall lizard have faced challenging circumstances. The sister species, the Lilford wall lizard, went extinct from the biggest islands of the Balearics, Mallorca and Menorca, possibly because of Romans bringing cats and other predators there 2,000 years ago—or there may have been a snake invasion at some point in the past, too. Today, Lilford’s wall lizard is listed as “near threatened” on the International Union for Conservation and Natural Resources’ Red List. But the Ibiza wall lizard’s situation is more dire, listed as “endangered.”

(This grumpy-faced lizard is under threat. Can its adorableness help save it?)

A colorful snack

Scientists trace the arrival of Ibiza’s horseshoe whip snakes to the winter of 2003, when olive trees were imported from the Spanish mainland for home landscaping purposes. "Having a very big olive tree, like, larger than your neighbor, is some sign of social status in a way,” Lapiedra explains. Snakes must have hid in tree trunk cracks and crevices in a hibernation-like state during cold weather, Lapiedra says, and then became active when the weather warmed after transportation. Some of the first snake sightings on Ibiza were recorded in plant nurseries in the villages of San Lorenzo and Santa Eularia.

For the first few years, the snake population remained stable. Then came the spread: Feeding on lizards, the snakes reproduced rapidly. According to the Current Zoology study, environmental officers and island residents started noticing lizard numbers dwindling beginning in 2010.

But the lizards faced a surprising conservation hurdle: Horseshoe whip snakes have a protected wildlife status on the Spanish mainland. Efforts to limit their spread could not begin on Ibiza unless the Spanish government designated the snake as invasive to the island. That didn’t happen until 2013, a few years after they had already begun expanding their territory and impacting the lizards, says Anna Torres, director general of natural environment and forest management of the Government of the Balearic Islands.

Since Ibiza wall lizards have largely lived without predators for millions of years, they were particularly vulnerable, exhibiting something scientists call island tameness. “They have evolved in a context where they didn't have to be afraid of anything,” says Lapiedra. And so they don’t necessarily flee when they see a snake coming.

Lapiedra’s group, which includes Casbas, is exploring if the lizards are adapting their behavior in the face of the snake threat. Their preliminary experiments, which involve putting lizards into a controlled setting with dry stone walls, have found that lizards that come from areas where they coexist with snakes tend to show more caution, taking more time to look around for predators, compared to lizards from areas without snakes. Further research will be needed to figure out whether individual lizards are learning to become more cautious and vigilant, or whether guardedness is an inherent attribute of many lizards that have survived being eaten so far.

Even in the most optimistic adaptation scenario, the snakes may still overwhelm the lizards. The horseshoe whip snake is normally a terrestrial reptile—yet scientists have seen them swim from Ibiza to other islets—as documented for the first time in a new study by Casbas and colleagues in the journal Ecology. Even one snake on a tiny islet can foreshadow the end of an entire lizard population.

Elba Montes, a biodiversity researcher at the Spanish Association of Herpetology, fully dove into studying the plight of the lizards for her doctoral work, kayaking and sometimes even swimming from islet to islet with only a phone in a plastic bag. She had found that on the small islet of S’Ora, where lizards were reported as of August 2017, not a single lizard roamed during her 2018 and 2019 visits; no lizard excrement or skin sheddings remained, either. She and colleagues think that the population had gone extinct in a matter of 10 months at most, given that a snake was recorded swimming in the sea nearby in April 2018.

“In light of our disturbing findings, a reassessment of this lizard’s conservation status needs to be done, and managers now have an urgent duty to improve snake management to avert its extinction,” she and her co-authors wrote in Current Zoology.

For humans, the snakes present no danger; Montes says she has been bitten many times. Their teeth are tiny, and they don’t have venom, so the most damage they can do to a human is a small pierce of the skin. Lizards, on the other hand, are so small and tame that they are akin to “gummies” or other snacks for snakes. 

“They catch them like nothing— it's like if they were, I don't know, popcorn,” Montes says.

Solving genetic mysteries before it’s too late

As the lizard populations decline, scientists are racing to study their remarkable biology—and get closer to solving the mystery of why they come in some many different colors.

“These lizards are a powerful system to address broader questions about how and why color variation arises in nature,” García-Roa says. These are similar questions to what Charles Darwin studied more than 160 years ago.

In pursuit of answers, García-Roa, collaborating with Uller’s laboratory, painstakingly documented the diversity of lizards on dozens of islets—both the Ibiza wall lizards and their sister species found near Mallorca—through photography, and clipped tiny sections of the tails of different groups to be used in genetic analyses. He completed this survey in several bursts from 2022 to 2025, including fieldwork in hard-to-reach rocky islets that can only be visited with a permit. Some lizard groups he photographed in that time have since gone extinct.

Collectively, the team that Uller oversees has collected DNA samples from nearly 2,000 wall lizards in the Balearic Islands. This effort is now feeding into the most comprehensive analysis to date of the lizards’ appearances and genetic variations. The team is working on putting it all together in a study that quantifies, for the first time, how much diversity—both in terms of how the lizards look and their genomes—would be lost if more of these groups of lizards disappear.

To date, the scientists have yet to find definitive answers about the origins of the Ibiza wall lizards’ distinct colorations and patterns. There’s not yet a one-to-one formula for predicting which genetic variations lead to which appearances.

“Even though we cannot yet provide a definitive answer, our expectation is that what we are seeing is a combination of genetic and environmental influences,” García-Roa says. “In other words, each population may express these color traits depending on environmental factors, within the limits set by their genetic backgrounds.”

Genetic factors may underly the regulation of pigment cells, which produce different hues and give rise to distinct patterns, Feiner says. Even in zebrafish, which are commonly studied in labs across the world, the genetic mechanisms underlying their stripes remain mysterious, Feiner notes. “In lizards, where the patterns are way more complex, it’s even more difficult,” Feiner says. “But that makes it exciting as well.”

(10 lizards were smuggled into Cincinnati in a sock. Now there are tens of thousands.)

Breeding new generations

Today, locals on Ibiza are keenly aware of the snake problem, and want to help preserve their local mascots. Citizen science reports have helped Casbas and colleagues track the snake expansion over time. Snake trap designs have improved since Montes first began work on a pilot trapping project in 2014, and many island residents have deployed them in their gardens, baited with mice. The concept is still being improved upon; in the future, there could be a chemical attractant for the traps instead of rodents, Montes says.

On mainland Spain, efforts are underway to breed more lizards to preserve their genetic diversity. In June 2025, the first dozen Ibiza wall lizard babies were born at the Barcelona Zoo, and a new program is set for Bioparc Valencia, Valencia’s zoo. Torres, from the Balearic Islands’ regional government, says the goal is to expand this breeding program with more partner institutions.

In the coming months, Lapiedra’s team will collect more lizards from the archipelago to take back for the zoos’ breeding program. The effort makes Lapiedra feel like he and fellow scientists are establishing the passenger manifest for Noah’s Ark.

“Because it's playing like, ‘Okay, you're the one who's going to survive, and you're not, because I didn't catch you,’” he says. “It's weird, honestly, as a human being, to have this feeling.”

Casbas, who lives in Barcelona, arrived in Ibiza last month for a season of fieldwork. He was relieved to see his lizard friends at his sea-view lunch hangout, and brought two graduate student collaborators to share the vista. “New students enjoying that beautiful spot makes me feel alive,” Casbas says. And with new students, comes hope. The more scientists that become entranced with these unique creatures, the better the chances at survival they might have.