Reptiles
Desert Iguana
Dipsosaurus dorsalis · also called desert iguana
The desert iguana is a pale, unassuming lizard of the North American deserts, and its trick is heat. When the ground is hot enough to cook an egg and every other reptile has bolted for a burrow, the desert iguana is often just getting started — foraging on creosote leaves at a body temperature approaching 45°C, one of the highest any lizard willingly tolerates.
Overview
The desert iguana lives in the Sonoran and Mojave deserts of the south-western United States and north-western Mexico, on sandy flats with creosote bush. It is about 40 cm long, half of that tail, pale grey to tan with a fine reticulated pattern and a low back crest. It is one of the few mostly plant-eating lizards, favouring creosote leaves, buds, and yellow flowers.
Built for heat
It stays active at body temperatures of 42–45°C, briefly tolerates close to 48, and has one of the highest preferred body temperatures of any lizard. In summer it is often most active around midday, climbing into bushes for cooler air and fresh leaves above the scorching ground — hours when it has the desert largely to itself.
A specialised gut
To live on tough, resinous desert plants it relies on fermenting gut microbes, which themselves work best at the high temperatures the lizard maintains. It digs a burrow to retreat to at night and in extreme conditions, and can sprint on its hind legs when chased.
Status
The desert iguana is Least Concern, common and stable, with no significant threats beyond localised habitat loss.
Desert Iguana: common questions
How does the desert iguana tolerate such high temperatures?
It combines behaviour, physiology, and biochemistry. Behaviourally, it shuttles between sun, shade, bushes, and its burrow to fine-tune its temperature, and it can simply operate at a hotter set point than most lizards, preferring a body temperature that would be dangerous to many reptiles. Physiologically, its cells and proteins are more resistant to heat damage, it produces protective heat-shock proteins readily, and it can lose some heat by panting. It also gains an advantage by being active when few predators and competitors are, effectively having the hottest part of the day to itself.
Why does it eat creosote bush, which most animals avoid?
The creosote bush is one of the most abundant and reliable plants in the North American deserts, but its leaves are coated in resins and compounds that deter most herbivores. The desert iguana has adapted to tolerate and digest it, drawing on a gut full of fermenting microbes to break down the fibre and, to some degree, cope with the plant chemistry. Being able to use a food that is always there, when the flush of annual wildflowers it also relies on is seasonal and unpredictable, is a big advantage in a harsh, variable environment.
Is the desert iguana related to the green iguana?
They are both iguanas, in the family Iguanidae, and both are largely plant-eating lizards, but they are not close relatives and they live very different lives. The green iguana is a large, tree-dwelling animal of Central and South American rainforest. The desert iguana is a much smaller, ground-dwelling, burrowing lizard of the arid North American southwest, and it is the only species in its own genus. Its scientific name, Dipsosaurus, means thirsty lizard, a reference to how well it copes with a dry, hot habitat.
Is the desert iguana dangerous or kept as a pet?
It is harmless. It has no venom, a small mouth, and a shy disposition, and it will flee into a burrow rather than confront anything. It is kept occasionally by reptile hobbyists but is considered a challenging species, because it needs very high basking temperatures, intense UV light, a deep substrate to dig in, and a specialised largely herbivorous diet, and wild-caught animals often settle poorly. Most people encounter it as a pale shape darting between creosote bushes on a hot desert afternoon.