“Snake-proof bunker” created to protect the Ibiza wall lizard

The Regional Ministry of Agriculture, Fisheries and Natural Environment presented the first “safe refuge” for the conservation of the Ibiza wall lizard (Podarcis pityusensis) today at the Can Marines agricultural estate in Ibiza. The new protection measure will allow populations to be kept safe from the growing threat posed by invasive snakes.

The refuge’s security is based on “scientific criteria and long-term monitoring”, as well as “planned management and genetic control”, according to explanations given to the media at an event attended by the regional minister for Agriculture, Fisheries and Natural Environment, Joan Simonet; the director general for Natural Environment and Forest Management, Anna Torres; the head of the Species Protection Service, Tomeu Moragues; and the service’s senior biology technician, Irene Garneria.

It is a “snake-proof bunker” built from conglomerate material and standing around 170 centimetres high. At its highest point, it has overhanging panels that fold outwards, creating an obstacle that snakes are unable to overcome, according to the technicians. Lizards outside the refuge, or even those already inside it, are also unable to cross this barrier.

One of the technicians explained to this newspaper that similar systems are built in Texas to protect people from rattlesnakes as their numbers increase, although in that case they are designed to protect human lives rather than lizards.

It has outward-folding overhangs, an obstacle that snakes are unable to overcome

A bulky structure covered in snails

The installation, a fairly imposing rectangular structure, covers an area of around 100 square metres and has been specifically designed to prevent invasive snakes from entering while providing the best possible conditions for the lizards’ survival.

It contains native vegetation, including a fig tree, a strawberry tree, lavender, marigolds, thyme, mastic trees and rockroses, as well as rock structures, natural shelters made from logs, a supply of water in the form of a small pond and suitable habitats to encourage the presence of invertebrates, which are the lizards’ main source of food.

What it does not prevent is the arrival of snails, which cover the walls. “It is another sign that there are few lizards. There is a plague on the island because they are not being eaten when they are small”, the technician explains.

In addition to the refuge presented this Wednesday, the Regional Ministry plans to build three more safe refuges in Ibiza. Another will be constructed at the public estate of sa Coma and, “depending on the results, the possibility of building” two more will be considered: one at the agricultural experimentation estate and another at the former military barracks.

CREAF researcher Oriol Lapiedra developed the design of these refuges, which has been incorporated into the project under the collaboration agreement between the Regional Ministry of Agriculture, Fisheries and Natural Environment and the Barcelona Zoo Foundation.

The refuges represent a new phase in the conservation strategy jointly promoted by both institutions, following the positive results achieved through the ex situ breeding project for the Ibiza wall lizard. This infrastructure will be able to house specimens from that programme and from particularly vulnerable populations in the Pityusic Islands, with the aim of creating new stable populations in safe environments.

Private individuals warned not to create their own refuges

During the presentation of the safe refuge, Simonet, Torres, Moragues and Garneria all warned that this type of facility can only be created by the Balearic Government because “the breeding of protected species, such as Podarcis pityusensis, must always be carried out under scientific supervision and by the competent administration”, in this case the Balearic autonomous community.

They stressed this point several times because they have received reports that at least one private individual has already created something similar. “We are hearing things”, they said.

The Natural Environment department warns that, rather than helping, closed lizard populations of this kind could first create a problem of inbreeding and would also fragment the habitat, thereby “cutting off gene flow”.

“This must be planned by the administration. We understand that people want to help, but...” they insisted.

“This must be planned by the administration. We understand that people want to help, but...”

The snake capture operation has been progressively strengthened in recent years. Last season alone, more than 4,400 invasive snakes were captured in Ibiza and Formentera.

However, the Regional Ministry is aware that these traps could be made more effective, something it believes could be achieved, for example, by using pheromones to attract the snakes. In this regard, the Natural Environment department is applying for a LIFE project worth around five million euros, which also includes safeguarding the phenotypic and genetic diversity of the endemic lizards and the use of whole-genome sequencing.

The project will also create new lines of research, including the genetic selection of lizards capable of escaping snakes, which they do not yet recognise as predators because the invaders are relatively new to the islands, and the possible coexistence of lizards and low numbers of snakes in controlled areas.

In theory, in mainland areas where ladder snakes, the most common species in Formentera, or horseshoe whip snakes, the most widespread in Ibiza, are present, lizards do not become extinct. The difference is that on the mainland both snake species must contend with their natural predators, which do not exist in the Pityusic Islands.