Are Frogs Cold-Blooded? (Surprising)

Frogs are cold-blooded and you may be surprised at how much of an advantage this can be for their survival in the wild. When I was a kid, I thought that being cold blooded meant that their blood was cold so they could survive the cold Winter temperatures, but that is not entirely true.

Frogs are cold blooded animals, or ectotherms, meaning that frogs rely on their environment to maintain their body temperature. Frogs generally require less food, can live in harsher environments, and are less likely to carry blood diseases compared to endotherms, or warm-blooded animals.

Although many people think that cold-blooded means frogs generally have “cold blood” this is in fact an incorrect interpretation of what “cold-blooded” means. Let’s have a much more precise look at the definition of cold-blooded, and what it means for frogs and their survival in the wild.

What Does Cold-Blooded Mean?

Cold-blooded animals are ectothermic, a word that derives from the Greek words “ecto” meaning “outer” and “thermic” meaning “heat.” Therefore, ectothermic or cold-blooded means that such animals rely on their environment to maintain their body temperature.

So the fact that frogs are cold-blooded does not mean they have cold blood or thrive in colder temperatures. It simply means that for cold-blooded animals, their environment is their main influence on their body temperature, and for endotherms, or warm blooded animals, their body temperature is maintained by their metabolism.

Therefore, warm blooded does not mean that mammals, like humans, are always hot, and cold-blooded animals, like frogs, are always cold. Being cold-blooded, warm-blooded, or both simply means that animals regulate their body temperatures differently.

The confusion that cold and warm-blooded engender is one of the reasons why scientists prefer the more precise terms ectotherm (“cold-blooded”), endotherms (“warm-blooded”) and heterotherm (presenting characteristics of both cold or warm blooded).

Why Are Frogs Cold-Blooded?

Generally, frogs being cold blooded, or ectotherms, is an advantage to their survival because they generally require less food, can live in harsher environments, and are less likely to carry blood diseases compared to endotherms, or warm blooded animals.

Cold-Blooded Frogs Need Less Food

Since frogs are cold-blooded, they generally require less food compared to warm-blooded animals. Warm-blooded animals need to eat often to maintain their body temperature, whereas a frogs’ body temperature fluctuates depending on the outside temperature.

When the weather is warm, frogs are more active and quick. They absorb the heat which gives their muscles the energy they need to spring into action, their metabolism speeds up, and they tend to be more alert. But when temperatures are low, frogs are more lethargic, they tend to be slower, and require less food to survive.

Nocturnal ectotherms like many frog and toad species that live in colder regions are generally ambush predators, meaning that they sit and wait for prey to come to them. This hunting technique requires little energy and frogs can catch prey from distances up to .33 times their body length thanks to their long tongues.

Cold-Blooded Frogs Can Live in Harsh Environments

Since frogs do not need to eat constantly to maintain their body temperature, they can live in harsher environments with less food. For example, North American frogs and toads hibernate all Winter and do not eat during multiple months. Many North American tree frogs even freeze 40% to 65% of their bodies’ water content during hibernation.

Certain fogs in the Southern Hemisphere also spend multiple months without food. During dry seasons, frogs estivate in environments where there is no water for long periods of time. Estivation is a period of dormancy similar to hibernation but in response to different conditions. Instead of getting out of the cold, frogs that estivate escape the heat.

Hot or arid conditions are not ideal for frogs that are cold-blooded and require water and humidity to survive, so estivation is key to survival for frogs in hotter climates depending on the Season.

Cold-Blooded Frogs Are Not Good Hosts to Sicknesses

Since frogs are cold-blooded and their body temperature fluctuates, their blood and organs are not good hosts to viral or bacterial diseases that prefer maintained, warm temperatures to thrive. Therefore, frogs and toads tend to carry less sicknesses in their blood compared to warm-blooded animals.

However, although frogs may not be the best hosts to viral or bacterial diseases in their blood, they can still carry such diseases on their skin. Although the mucus on frogs skin may contain chemicals that can kill certain viruses, bacteria, and fungus, these illnesses can still be transmitted to humans.

That is one of the reasons why wearing gloves is so important when handling frogs. Not only can they protect you from a potential viral or bacterial disease frogs can carry on their skin, it can also protect you from their poison if you are holding a poisonous species.

Being Cold-Blooded Can Be a Disadvantage to Frogs

Frogs being ectotherms present a disadvantage due to climate change. Certain frog species can tolerate temperatures beyond 40°C, however, climate change, loss of habitat and forest conversion is affecting frog populations around the world.

Temperature and the presence of water are two of the most important variables affecting frog and toad body temperature, evaporative water loss and metabolic rate (Mokhatla et al, 2019). When these are disrupted by climate change, loss of habitat, and forest conversion, the frogs may be able to adapt, or they may die.

“Amphibians that tolerate higher temperatures are likely to fare better in a world affected by climate change, disease and habitat loss, according to two recent studies from the University of California, Davis.”

The ambient temperature and energy availability are key factors that influence how well cold-blooded frogs can function. When the temperature is too hot, water evaporates and poses a risk for frogs’ health since their skin needs to stay hydrated for them to be able to breathe and drink.

How well frogs adapt to climate change are dependent on a variety of factors including the species and their temperature tolerance, how well they can alter their body size, energy demands, and how well their food (bugs, rodents, etc) also adapt to climate change within their environment.

Can Frogs Freeze to Death?

Frogs can freeze to death if directly exposed to the cold as toads are not freeze-tolerant and have been reported to die at temperatures between –1.5°C to –5.2°C (or 29°F to 23°F). Tree frogs are more freeze-tolerant since 40% to 65% of their bodies’ water content freezes during hibernation.

Toads hibernate on land, generally at depths of 1 m or 3 ft below the frost line. Toads that inadvertently expose themselves to the Winter’s chill may die. Toads are not freeze-tolerant and have been reported to die at temperatures between –1.5 to –5.2 °C or 29°F to 23°F (Swanson et al. 1996).

Like toads, aquatic frogs may die if exposed to temperatures below –5°C or 29°F. Aquatic frogs generally sit, float, or slowly swim at the bottom of ponds during Winter. Oxygen levels are high below 4°C or 39°F and provide a great environment for them to hibernate.

North American tree frog species are much more freeze-tolerant and generally freeze between 40% to 65% of their body’s water content during Winter. When a tree frog freezes solid, it stops breathing, its heart stops, and the frog appears dead.

When tree frogs hibernate, their liver produces large amounts of glucose, thereby increasing blood sugar levels. The elevated blood sugar acts as “antifreeze,” which prevents the formation of ice crystals in the body.

Learn moreo about how frogs hibernate in this dedicated guide on our blog.

Do Frogs Like Hot or Cold?

As a general rule, most frogs in the Northern Hemisphere thrive between temperatures of 0°C and 30°C, but some frogs can survive temperatures as low as -5°C and as high as 41°C. Frogs or toads may naturally thrive, adapt or perish due to temperature depending on the species and environment.

In one study, the frog that were examined had body temperatures ranging from 15°C to 21°C (59°F to 70°F) in the wild on a warm day. During lab tests, frogs hit their pique performance in a jumping test at 15°C (59°F), but were less performant below 6°C (43°F) (Köhler et al, 2011). Another study found that “energy ingestion, linear growth, weight increase and gross conversion efficiencies were all maximal at 27°C” (Bayard, 1979).

A study (King, 1903) found that the optimal temperature for one frog species’s eggs to develop is 20°C to 30°C (68°F to 86°F) depending on the stage of development and time of year, whereas the toad species in the study lays their eggs in shallow pools of water that heat up easier, so their eggs can withstand higher temperatures around 28°C (82°F).

Frogs thrive at different temperatures depending on the species, but overall they tend to select favourable, moist and cool habitats of intermediate temperature to reduce their water loss and reach their peak physiological and behavioural performance. Frogs hibernate or estivate when temperatures are too cold or too hot for them to handle for long periods (CTNF).

Frogs generally avoid the heat during the day by staying out of the sun. You can find toads burrowed during the day, and aquatic frogs submerged in water in the shade of abundant vegetation. Frogs tend to avoid full sun at all costs since they breathe and drink through their skin that needs to stay moist for many species to be able to survive.

More About Cold-Blooded Frogs

This blog is all about toads and frogs and you can learn more about them and how they live in the wild in the dedicated guides on our blog below:

Common Questions About Cold-Blooded Frogs

Do frogs come back to life? Frogs cannot come back to life if they are dead. However, tree frogs come back to life after being frozen with their vital organs like their heart and lungs stopped during Winter. 40% to 65% of tree frogs’ water content freezes during hibernation and they survive by producing glucose in their body.

How hot can frogs get? Generally, some frog species can survive temperatures up to 41°C, however such heat is not ideal for most frog species due to dehydration. Frogs generally prefer temperatures between 0°C and 30°C.

How cold can frogs survive? Many North American tree frog species can survive extreme temperatures below -7°C or 19°F. However, aquatic frogs avoid freezing temperatures by remaining in water above freezing yet below ice, and toads cannot survive temperatures below –1.5 to –5.2°C or 29°F to 23°F.

How cold is too cold for frogs? As a general rule, temperatures below freezing are too cold for aquatic frogs, –1.5 to –5.2°C or 29°F to 23°F is too cold for toads that die within and below such temperatures, but certain tree frog species can survive freezing.

Why can frogs freeze? Tree frogs like Gray Treefrogs, Cope’s Gray Treefrog, Boreal Chorus Frog, Spring Peeper, and Wood Frogs hibernate in cracks and under leaf litter at the foot of trees and generally freeze between 40% to 65% of their body’s water content to hibernate and survive Winter.

Are all amphibians cold-blooded? All amphibians are cold-blooded including frogs, toads, salamanders, newts and caecilians.

Sources

Bayard H. Brattstrom. 1979. Amphibian Temperature Regulation Studies in the Field and Laboratory, Department of Biology, California State University, Fullerton, California, 92634, AMER. ZOOL., 19:345-356.

Brooks, Stabler E. 1918. Reactions of Frogs to Heat and Cold. American Journal of Physiology-Legacy Content 1918 46:5, 493-501, https://doi.org/10.1152/ajplegacy.1918.46.5.493

King, H. 1903. The Effects of Heat on the Development of the Toad’s Egg. Biological Bulletin, 5(4), 218-232. doi:10.2307/1535737

Köhler, Angela & Sadowska, Julita & Maliszewska, Justyna & Trzeciak, Paulina & Berger-Tal, Oded & Tracy, Christopher. (2011). Staying warm or moist? Operative temperature and thermal preferences of common frog (Rana temporaria), and effects on locomotion.. Herpetological Journal. 21. 17-26.

Mokhatla M, Measey J, Smit B. The role of ambient temperature and body mass on body temperature, standard metabolic rate and evaporative water loss in southern African anurans of different habitat specialisation. PeerJ. 2019;7:e7885. Published 2019 Oct 22. doi:10.7717/peerj.7885

Swanson, D.L., B.D. Graves, and K.L. Koster. 1996. Freezing tolerance/intolerance and cryoprotection synthesis in terrestrially overwintering anurans in the Great Plains, USA. Journal of Comparative Physiology B 166:110–119

Science Daily, Frogs that can take the heat expected to fare better in a changing world

Climate change may outpace deforestation as habitat threat in tropics, July 7, 2016, University of California – Davis

Von May R, Catenazzi A, Santa-Cruz R, Gutierrez AS, Moritz C, Rabosky DL (2019) Thermal physiological traits in tropical lowland amphibians: Vulnerability to climate warming and cooling. PLoS ONE 14(8): e0219759. https://doi.org/10.1371/journal.pone.0219759