Lizards require water for survival, but the method by which they obtain it is incredibly diverse, often bypassing the typical “drinking” methods seen in mammals. Many species in arid environments have evolved specialized physical and behavioral adaptations to collect and process moisture. For some, active ingestion from a standing source is the primary means of hydration, but others rely on water from their diet or that is manufactured internally. The most ingenious methods involve collecting environmental moisture directly onto their skin and channeling it to the mouth.
Active Ingestion Methods
Many lizard species, particularly those living in temperate or tropical environments with available standing water, rely on active ingestion. This process is often less complex than the sucking or gulping motions of mammals, relying instead on the tongue and gravity. Species such as the European green lizard (Lacerta viridis) use their tongue to lap water from a surface in a coordinated four-phase sequence.
The lapping mechanism involves the tongue and gravity to move water through the buccal cavity and into the esophagus. Unlike many mammals, which create a liquid column or use suction, lizards typically dip the tongue into the water and then use coordinated head and tongue movements to draw the liquid back. This enables them to utilize water sources like dew drops on leaves, small puddles, or moisture collected on a vertical surface. For these species, actively drinking from a free-standing water source is the most direct way to replenish water lost through respiration and excretion.
Water Acquisition from Diet and Metabolism
For many lizards, especially those inhabiting deserts, the moisture contained within their food is the primary source of hydration, allowing them to survive long periods without drinking. Insectivorous lizards obtain a significant amount of water from their prey, as insects are naturally rich in moisture. Herbivorous species, such as iguanas, consume leafy vegetation like collard greens or bok choy, which can contain between 91% and 96% water by weight.
Beyond consuming water directly, lizards also generate metabolic water through the internal process of aerobic respiration. This is a biochemical reaction where the oxidation of fats and carbohydrates from food breaks them down for energy, producing water as a byproduct. Fat stores are particularly efficient for this purpose, yielding more than twice the amount of metabolic water per gram compared to carbohydrates. Highly desert-adapted species, like the desert iguana, rely heavily on this process, utilizing large fat reserves to sustain their water balance when external sources are unavailable.
Specialized Surface Collection Techniques
Some remarkable adaptations involve collecting water directly onto the skin and channeling it to the mouth, effectively bypassing the need for a water dish. The Australian thorny devil (Moloch horridus) is a prime example, using a complex network of microscopic channels between its scales to collect moisture. These channels operate by capillary action, drawing water from rain, dew, or even moist sand over the entire body surface and transporting it passively to the corners of the mouth.
The Texas horned lizard (Phrynosoma cornutum) employs a similar system, though its skin channels direct the flow toward the mouth, particularly when the lizard adopts a specific posture. When moisture reaches the mouth, the lizard uses repeated jaw movements to ingest the water collected from its skin. Certain geckos and chameleons also exhibit specialized scales that maximize the condensation of fog or dew, allowing them to absorb the moisture through the skin’s surface or channel it toward their mouths. These mechanisms allow lizards to exploit trace amounts of environmental moisture, enabling their survival in extremely arid climates.