Lizards rely on external temperatures for survival. Unlike mammals, they are ectothermic, meaning their body heat comes from their surroundings. This reliance makes them susceptible to temperature extremes, both high and low, which can quickly become lethal.
Understanding Lizard Thermoregulation
Lizards are ectothermic, absorbing heat from their environment rather than producing it internally. This also makes them poikilothermic, meaning their body temperature fluctuates with ambient temperature. While this allows lizards to conserve energy, it also makes them vulnerable to environmental temperature shifts.
To manage their body temperature, lizards employ behavioral strategies. They bask in sunlight or on warm surfaces to absorb heat, and conversely, they seek shade, burrow underground, or adjust their body posture to cool down. These behaviors are important because their physiological processes, including metabolism, digestion, and immune function, are directly dependent on maintaining a suitable body temperature.
Lethal High Temperatures
A lizard’s body temperature exceeding its optimal range can lead to severe consequences, culminating in death. When lizards overheat, their bodies experience protein denaturation, enzyme dysfunction, and organ failure, which can affect the kidneys, liver, and heart. Dehydration and heat stroke are also significant risks.
General lethal high temperatures for many common species are often above 100-110°F (38-43°C). For example, lizard embryos have been observed to die when exposed to 110°F (43°C) for just a few minutes. Signs of overheating include lethargy, decreased activity, loss of appetite, rapid panting or gaping, restlessness, disorientation, and a wobbly gait. In severe cases, seizures and unresponsiveness can occur.
Lethal Low Temperatures
Temperatures that drop too low can also be deadly for lizards. When a lizard’s body temperature falls below its tolerance level, its metabolic rate slows significantly, leading to organ shutdown and an inability to move or digest food. This state, known as hypothermia or cold-stunning, can result in tissue death or even complete freezing of the body.
While some species can tolerate near-freezing conditions, many lizards become helpless when temperatures fall below 45°F (7.2°C). This differs from brumation, a natural winter dormancy where lizards intentionally slow their bodily functions to survive cold periods. In cold-stunning, lizards lose control of their limbs and become unresponsive, a condition that can be fatal if they are not warmed appropriately. Observable signs of a lizard being too cold include lethargy, unresponsiveness, inability to move or right themselves, sunken eyes, and wrinkled skin.
Factors Influencing Temperature Tolerance
There is no single “death temperature” for all lizards, as their tolerance to temperature extremes varies widely based on several factors. Different species have evolved specific adaptations to their native climates; for example, desert-dwelling lizards generally tolerate higher temperatures than those from tropical or temperate regions. This species-specific adaptation means their ideal temperature ranges differ considerably.
Lizards can also exhibit a degree of acclimation, gradually adjusting their temperature tolerance over time if exposed to slowly changing conditions. A lizard’s age and overall health also play a role, with younger, older, or sick individuals often more vulnerable to temperature fluctuations. Hydration status is another important factor, as dehydration significantly reduces a lizard’s capacity to withstand high temperatures. Furthermore, larger lizards typically heat up and cool down slower than smaller ones, and environmental factors such as available shelter, humidity levels, and wind can all impact a lizard’s ability to regulate its body temperature.
Protecting Lizards from Temperature Extremes
For pet lizards, providing a controlled environment helps prevent temperature-related fatalities. Enclosures require proper heating elements, such as heat lamps, ceramic heat emitters, or heat mats, to create a thermal gradient with warm basking areas and cooler zones. Thermometers and thermostats are important tools for monitoring and maintaining these precise temperatures. Direct sunlight on an enclosure should be avoided, as it can quickly lead to dangerous overheating. Providing constant access to fresh, clean water also aids hydration, and misting can help maintain appropriate humidity levels for species that require it.
In the wild, lizards face increasing challenges from climate change and habitat destruction, which limit their ability to thermoregulate naturally. Human actions like providing shade or water sources in extreme conditions can offer some relief. Recognizing the signs of temperature stress in any lizard, whether pet or wild, is important. These signs include lethargy, heavy panting, disorientation, unresponsiveness, and a loss of appetite. When a lizard shows these symptoms, controlled cooling or warming is necessary, as rapid changes in temperature can cause further shock and harm.