The Pitiusan lizard.

An island species

The Ibiza wall lizard lives naturally only on the Pitiusas: Ibiza, Formentera and the small islets around them. It is a protected species.

It is often bright green, turquoise or blue, especially males in the breeding season.

Different on every islet

Populations on small islets have been isolated for a long time and can differ in colour and pattern from those on the main islands.

Scientists have described many distinct forms, which is part of why the islets matter for conservation.

Each islet has its own lizards, slightly different from the next.

How they live

They eat insects, fruit, flowers and seeds, and help pollinate some plants. They shelter under stones and in dry-stone walls.

In the hottest hours they hide; mornings and late afternoons are the best times to see them.

The threat from snakes

Snakes arrived on the Pitiusas in recent decades, thought to have come with imported ornamental trees. They prey on lizards, and populations have declined where snakes have spread.

Control programmes are under way, and the islets remain refuges.

How to help

Don't move stones or build stone stacks; they destroy shelters. Don't feed lizards or try to catch them.

Report snakes to the authorities if you see one, and never move plants or soil between islands.

Where to see them

Almost anywhere with stone walls and sun: villages, paths, lighthouses and beaches.

Sit still and they will come close.

The wall as habitat

Formentera's fields are divided by dry-stone walls, parets seques in Catalan, built without mortar from the flat limestone the island gives up easily. Every wall is a stack of gaps. To a lizard, a well-built wall is a cliff turned sideways: warm stone on the sunny face, cool crevices behind, and a hundred routes out of sight. Where the stones still sit tight, the wall holds the day's heat into the evening. Where it has collapsed into rubble, the lizards move down and carry on at ground level.

The plots the walls enclose are small and mostly worked lightly, which suits a species that wants cover within a short dash. A wall facing east catches the first sun and is busy early; one under fig trees stays quiet until the afternoon. Thick walls, with two faces and a rubble core, beat thin ones: more depth, steadier temperature, more places to disappear. A rendered and painted wall offers almost nothing, which is why the island's newer buildings hold far fewer lizards than the old stone ones.

The walls run for many kilometres across the island, linking one small field to the next, and each length of stone is a corridor as much as a boundary. Lizards use them to move between feeding ground and refuge without crossing open ground, where birds and cats patrol. A wall repaired in the traditional way, stone on stone, keeps working as habitat. One replaced with concrete block, or left to be swallowed by rubble and dry weeds, does not.

Reading a lizard's day

Lizards are ectotherms: their body temperature follows the stone they sit on, so the day is a schedule of moving in and out of the sun. On a spring morning the first animals appear on east-facing surfaces, flattened and dark, taking heat through the back. Once warm enough to move quickly they hunt, stopping every few paces to look. The wall is not decoration in this: it is the thermostat, the larder and the escape route in one structure.

By mid morning in summer the schedule changes. Heat that is useful at nine is dangerous at one, and the walls empty as lizards retreat into crevices, under loose stones or into the shade of a fig. The same animals reappear in the late afternoon, often in the same few metres of wall, because a good territory is worth keeping. A tail shorter than it should be, regrown in a duller colour, was shed to escape a predator.

Movement is easy to read once the pattern is clear. A male in breeding condition may hold his ground, flatten, and bob his head or push up on the front legs: a display aimed at another male, not at a passer-by. A female or a young animal slips away at the first shadow. Moulting lizards look patchy, as if the skin is peeling in flakes, which it is. None of this requires patience beyond standing still for a minute.

When the walls are busiest

Spring, roughly March to June, is the best window. Days are warm enough for activity but not so hot that the walls empty at midday, and the animals have other business: courtship, disputes over territory, feeding after the slow winter months. A mild morning after rain brings them out in numbers, though spring rain on Formentera is never guaranteed. Late summer is quieter by day, and the smallest lizards, quick and thin-tailed, usually appear then.

August is the month to adjust expectations. Between late morning and late afternoon the walls can look lifeless, and the animals are there all the same, a hand's depth into the stone. Walking the minor lanes at either end of the day shows a different island: low light on limestone, lizards on the top course of the wall, geckos not yet out. Geckos take the night shift on the same buildings, so the walls are never truly unoccupied.

Winter is quiet, and much of the island's tourist business closes from November to April, so a visit then is not a lizard trip. On mild, sunny days a few animals come out to bask, dark and flat against warm stone, and a wall facing the low sun is the place to look. Otherwise the population sits dispersed in crevices and under stones, waiting. On a cold wall in January the whole summer's activity is hard to imagine.