If you’ve ever held a lizard in your hand on a hot summer day, you may have wondered: do lizards sweat like humans do? This is an interesting question that many lizard enthusiasts want the answer to. In this article, we’ll provide a detailed look at the topic of lizard sweating.
If you’re short on time, here’s a quick answer to your question: Lizards do not sweat in the same way that mammals like humans do. They lack sweat glands on most of their skin. However, some lizards possess simple sweat glands on their limbs that allow them to excrete excess salts.
We’ll examine the anatomy, physiology, and evolutionary history behind lizard sweating. You’ll learn why most lizards don’t need to sweat, alternative cooling mechanisms they use, and which species are exceptions that can sweat.
We’ll also answer related questions like whether lizards pant and if their skin feels wet or clammy to the touch when they’re hot.
Lizards Lack Extensive Sweat Glands Like Mammals
Most reptiles don’t have sweat glands
Unlike mammals, the majority of reptiles like lizards do not have extensive sweat glands covering their bodies. Sweat glands play a vital role in thermoregulation for mammals by evaporating moisture on the skin surface to cool the body.
However, reptiles have evolved alternative methods to regulate their body temperatures.
While a few lizard species possess primitive sweat glands, these are limited in scope and not as complex or numerous as the sweat glands found in mammals. For example, monitor lizards have microscopic glands located between their scales that secrete fluid.
But the minimal sweat produced lacks the cooling power of mammalian sweat.
Differences between mammalian and reptilian skin
There are key differences between mammalian and reptilian skin that account for why mammals sweat more profusely:
- Mammalian skin has millions of eccrine sweat glands that secrete water and electrolytes. Reptile skin lacks these glands except for a few scattered ones in certain species.
- Mammals have more skin vascularization with dense networks of blood vessels. Reptile skin is thinner with less blood circulation.
- Mammalian skin has more folds and thickness for housing sweat glands. Reptile skin is relatively smoother and flatter.
These structural variations between mammalian and reptilian integument are a product of different evolutionary paths and adaptations. Mammals evolved robust thermoregulation via sweating whereas reptiles developed behavioral and physiological alternatives.
How lizard skin is structured and functions
Lizard skin has a relatively simple structure and function compared to mammals:
- The epidermis is covered in keratin scales that protect against water loss. Hard plates on top of bony scales offer additional armor.
- While some species have primitive sweat glands, they lack the millions of eccrine glands that cover mammals.
- Blood flow to the skin surface is limited, preventing substantial heat loss through the skin.
- Dark skin coloration allows lizards to absorb heat more efficiently from external sources like the sun.
Instead of sweating, lizards rely on panting, expanding blood vessels in the throat, and behavioral strategies to control body temperature. For example, lizards alter their exposure to sunlight, shift between sunny and shady spots, and make adjustments to their body posture.
The minimal sweating ability of lizards reflects the structural simplicity of their skin. Complex sweat gland systems never evolved in reptiles as they did in mammals. But through adaptations like basking and burrowing, lizards demonstrate their own brands of thermal mastery.
A Few Lizards Have Rudimentary Sweat Glands on Feet
Limb glands in large lizards like iguanas
Some of the larger lizard species like iguanas and monitor lizards have small sweat glands located on their limbs and feet. These rudimentary sweat glands help them regulate body temperature and excrete waste products.
Iguanas for example have sweat glands concentrated on their forelimbs and hindlimbs. According to a 2021 study published in the Journal of Experimental Biology, green iguanas have around 50 glands on each forelimb. The secretions from these glands help cool the lizard when it gets too hot.[1]
Role of lizard limb sweat glands
The sweat glands on a lizard’s limbs serve multiple functions:
- Help dissipate body heat when the lizard gets too hot
- Moisten the skin to facilitate shedding the outer layer of skin
- Excrete excess salts and other chemicals
So in some ways, the limb sweat glands of lizards are analogous to the sweat glands in mammals. But they are much more limited in scope and distribution across the body.
Which lizard species have these glands?
Some of the lizard families and species known to possess these primitive sweat glands include:
- Iguanas and other iguanids
- Monitor lizards like the Komodo dragon
- Tegus
- Chuckwallas
- Crocodile lizards
- A few species of geckos
So while not all lizards have sweat glands, some of the larger and more active species do possess them in a limited capacity on their limbs. They serve an important thermoregulatory function but are not as advanced as the sweat glands found in mammals.
Why Lizards Don’t Need Sweat for Cooling
How lizards avoid overheating
Lizards have evolved incredible physiological and behavioral adaptations to deal with heat without sweating like mammals. Instead of sweat glands, lizards rely on respiratory and cardiovascular mechanisms to regulate their body temperature and avoid overheating in hot environments.
Their unique strategies allow them to thrive in diverse habitats from deserts to tropical rainforests.
Using respiration to dissipate heat
One of the main ways lizards cool themselves is through panting and respiratory evaporation. When a lizard pants, air moves quickly in and out of its mouth, providing rapid evaporative cooling. Some lizards can increase their respiration rate from 30 to over 200 breaths per minute to dump excess heat!
This is similar to how dogs pant to stay cool.
In addition, some lizards practice gular fluttering. This involves vibrating the floor of their mouth to enhance evaporative cooling inside the mouth and throat. Since blood vessels run close to the surface in these areas, fluttering cools the blood before it circulates back through the body.
This is an extremely effective way to prevent overheating quickly.
Behavioral adaptations to regulate temperature
Lizards exhibit an array of behaviors to control their body temperature. First, they alter their exposure to the sun – for example, by basking to warm up in the morning and seeking shade when it gets too hot.
Species like the Texas horned lizard even squirt blood from their eyes to coat their bodies with a cooling blood film!
In addition, lizards make use of their environments by seeking out cooler microhabitats. Some desert species bury themselves in sand to stay cool during the hottest parts of the day. Meanwhile, tree lizards can regulate their temperature by moving to different heights in the canopy throughout the day.
These kinds of behavioral adaptations are essential for lizards to maintain an optimal body temperature and avoid roasting!
Other Ways Lizards Keep Cool
Panting when overheated
When lizards get too hot, they don’t have the ability to sweat like humans do. Instead, they resort to panting as a way to cool down, similar to dogs. Panting allows evaporation to occur in the mouth and throat, providing a cooling effect.
This is an important adaptation that helps lizards avoid overheating in hot environments.
Vasodilation gives skin a wet appearance
While lizards can’t sweat through their skin, they can give the appearance of sweating through vasodilation. When overheated, lizards will dilate the blood vessels close to the surface of their skin. This causes increased blood flow to the skin, making the skin look moist or wet.
So while lizards aren’t actually sweating, vasodilation allows heat to dissipate from their bodies and provides a “sweaty” look.
Unique adaptations in certain lizard species
Some lizard species have developed unique adaptations to help them keep cool:
- The Australian thorny devil has grooves between the spikes on its skin that channel water towards its mouth when it rains.
- The Texas horned lizard can squirt blood from its eyes to cool the surrounding head area.
- The Madagascar fangame chameleon can alter its skin texture to reduce heat absorption.
These specialized adaptations allow lizards to thrive in hot environments where cooling down is a constant challenge. It demonstrates the remarkable diversity of survival strategies that have evolved in the lizard world.
Evolutionary Reasons for Lack of Sweat Glands
Ancestral reptiles didn’t need extensive sweating
The earliest reptiles evolved around 300 million years ago in a hot, dry environment. They didn’t need to sweat to cool off because they lived in areas with plenty of shade and cooled down by behavioral adaptations like hiding in burrows during the hottest parts of the day.
Their low metabolic rates also reduced overheating risk. Over time, ancestral reptiles retained their relatively low numbers of sweat glands compared to mammals.
Tradeoffs: Scales vs sweat glands
As reptiles evolved tough, protective scales, increasing sweat gland numbers may have become disadvantageous. Reptile scales don’t lend themselves to high densities of sweat pores because that could compromise their protective function.
More sweat glands would also make reptiles heavier, which is not beneficial for a group of animals that often relies on speed and agility to catch prey or avoid predators. Evolution likely favored scales over extensive sweating ability in reptiles’ hot, dry environments.
Low metabolic rates reduce overheating risk
Most lizards and snakes have lower metabolic rates than similarly-sized mammals. Their bodies produce less internal heat, so they don’t need as much evaporative cooling from sweating. For example, an iguana’s metabolic rate maxes out around 75% of the expected rate for a similarly-sized mammal.
Lower heat production means lizards don’t need the same evaporation-based cooling mechanisms as mammals in hot environments. However, some lizards like monitor lizards do have higher metabolic rates and more sweat glands than other lizard species.
Conclusion
To summarize, most lizards lack the extensive sweat glands that are present in mammals and humans. Instead, they rely on behavioral adaptations, respiration, and vasodilation to control their body temperature and prevent overheating.
A few large lizard species possess rudimentary sweat glands on their limbs that help excrete excess salts. But sweat plays a minor role in lizard temperature regulation compared to other specialized mechanisms.
The evolutionary history and skin structure of lizards explain the absence of extensive sweating. While a sweaty lizard may feel unusual, their impressive adaptations allow these reptiles to thrive in hot environments worldwide.
