Like humans, frogs need water to survive. Water plays a vital role in the regulation of frogs’ body fluids, and allows their bodies to keep up with important functions, such as getting rid of wastes and bringing nutrients to cells. But how do frogs drink water?
Frogs do not drink water through their mouths like we do. Instead, they rehydrate by absorbing water across their permeable skin, in a process known as ‘cutaneous absorption’.
Many frogs have a specialized area of skin located in the ventral pelvic region known as a ‘drink patch’, which is responsible for as much as 70 percent of their total water uptake.
That said, most frogs will occasionally swallow small amounts of water when they submerge their heads in water. Still, most of their fluid uptake will be across the skin.
Do Frogs Drink Water?
Frogs need to consume water to survive. Dehydration can be harmful, and even potentially lethal to most frogs. Their need for water is as critical as their need for food or oxygen–it’s an essential substance, that keeps their bodies working normally.
Frog bodies need a steady supply of fluids to transport nutrients, eliminate waste, and perform many other important functions.
As earlier mentioned, frogs generally acquire water by absorption across their skin rather than by oral drinking.
Amphibians have unique skin compared to that of many other vertebrates. Their skin is composed of thin membranous tissue that is quite permeable to water and contains a large network of blood vessels.
This permeable skin distinguishes them from mammals, birds, or reptiles.
Permeability relates to how easily a gas or liquid molecule can pass back and forth from the environment into the animal and vice versa.
Typically, the larger the molecule, the more difficult it is to enter the animal through its skin. Amphibian skin is more permeable than that of other vertebrates.
Their membranous skin allows water and respiratory gases to readily diffuse directly down their gradients between the blood vessels and the surroundings.
Many toads are even known to rehydrate by absorbing moisture from moist soil, through their skin.
How Do Frogs Drink Water?
Although most of a frogs’ skin is permeable to water, many frogs have a specialized area of skin located on their belly and the underside of their thighs (the ventral pelvic region), known as the ‘drink patch’, ‘drinking patch’, or the ‘seat patch’. This area of skin is responsible for most of their water uptake.
The drink patch has a very large network of small blood vessels called capillaries. Water absorption across this skin is driven by the osmotic gradient that develops as a consequence of solute transport.
In simple words, the skin acts in concert with the kidney and urinary bladder to maintain fluid balance
During periods of rehydration, frogs adopt a posture known as “water absorption response” (WR) – in which they thrust their hindlimbs backwards and press the belly surface onto any surface containing water.
Even though the drink patch skin only constitutes about ten percent of the total skin area, it is responsible for over 70 percent of the total water uptake by many dehydrated frogs.
Do Frogs Feel Thirsty?
In mammals, thirst motivates water seeking and consumption. It involves the stimulation of the thirst center in the hypothalamus as a result of a decrease in the volume of the extracellular fluids.
Some amphibians appear to seek water in which to lie in order to rehydrate.
This has led some researchers to suggest that this process may constitute a ‘primeval thirst’, which is quenched by the absorption of water across the skin, instead of by oral drinking.
What Sources Do Frogs Use to Rehydrate?
Frogs generally seek out bodies of fresh water in which they can soak and lie – to rehydrate. Many frogs love to hang around ponds and other freshwater bodies where they can rehydrate, and keep their skins moist.
In rainy weather, it’s common for frogs to come of out their retreats, and soak in rain puddles on the ground. While they soak in water, they absorb some of the water through their skin and rehydrate.
Many frogs also rehydrate by absorbing dew, and those that live in very humid environments can hydrate by absorbing the moisture in the air through their skin.
In addition, some frogs and toads also rehydrate by absorbing moisture from moist soil, or any other moist material, such as damp leaf litter.
Toads can absorb moisture through their skin even when they are underground. This is especially useful because they spend a lot of their time tunneled under the soil to escape the drying heat of the sun.
To avoid the hottest summer days and freezing winter cold, they also shelter in deep burrows made by other animals such as rodents.
Some Frogs Can Survive for Several Months Without Direct Access to Water
Most tree frogs live in environments where they can easily rehydrate by absorbing moisture in their surroundings, through their skin.
If the humidity levels around them are low, some tree frogs have a more creative way to hydrate.
Researchers from Charles Darwin University in Australia found that Australian green tree frogs (Litoria caerulea) survive the dry season by ‘fogging up’ like a pair of glasses.
On cool nights, Australian tree frogs sit down outside – and when they return to their dens, condensation will form on their cold skin.
This is similar to the condensation that happens when you take a cold drink out of the refrigerator.
The researchers conducted a series of experiments to see if the frogs could collect enough moisture through condensation to compensate for what they lost being in the cold.
They found that a cold night out cost a frog as much as .07 grams of water – but a frog could gain nearly .4 grams, or nearly 1 percent of its total body weight, in water upon returning to the warm den.
The researchers also found that as much as 60 percent of each water drop could be absorbed – proving that frogs can use condensation to rehydrate themselves.
Frogs Occasionally Swallow Small Quantities of Water
Although frogs generally do not orally drink water to rehydrate, many frogs are known to occasionally swallow small quantities of water. This can happen when they submerge their heads in water.
In one study, northern leopard frogs (Lithobates pipiens) were dehydrated until they had lost water equivalent to about 30% of their body weight.
When placed in tap water, the frogs rapidly regained this lost water, and 1·4% of the total water uptake was taken up by drinking.
In the same study, African clawed frogs (Xenopus laevis), were also dehydrated until they lost water equivalent to about 26% of their body weight.
When placed in fresh water, they regained their lost weight very slowly and after 2 hours in tap water, had only reaccumulated one-fifth of the water which they lost – with drinking making up 8% of the total water uptake.
According to the same study, this drinking was not in response to dehydration (primary drinking), but appeared to constitute ‘secondary’ drinking, which was not directly related to osmotic need.
Little scientific research has been done on this topic, and it’s not clear why some frogs occasionally orally drink small quantities of fluid.
Commonly Asked Questions
Do frogs drink water? Like humans, frogs consume water to keep their bodies functioning normally. However, frogs do not drink water through their mouths, but rather by absorbing it through their skin. Many frogs have a specialized skin area located in the ventral pelvic region known as a ‘drink patch’, which is responsible for most of their water uptake.
How do frogs drink water? Frogs do not drink water through their mouths as we do. Instead, they absorb it through their permeable skin. Many frogs have a specialized area of skin located on their belly and the underside of their thighs known as a ‘drink patch’, which is responsible for most of their water uptake.
Sources:
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Fitzsimons, J.T. (1975). Thirst and Sodium Appetite in the Regulation of the Body Fluids.In: Peters, G., Fitzsimons, J.T., Peters-Haefeli, L. (eds) Control Mechanisms of Drinking. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-61907-6_1
P.J. Bentley, K. Schmidt-Nielsen, Acute effects of sea water on frogs (Rana pipiens), Comparative Biochemistry and Physiology Part A: Physiology, Volume 40, Issue 2, 1971, Pages 547-548, ISSN 0300-9629, https://doi.org/10.1016/0300-9629(71)90047-8.
U. Katz; NaCl adaptation in Rana ridibunda and a comparison with the euryhaline toad Bufo viridis. J Exp Biol 1 December 1975; 63 (3): 763–773. doi: https://doi.org/10.1242/jeb.63.3.763
Malcolm S. Gordon, Vance A. Tucker; Osmotic Regulation in the Tadpoles of the Crab-Eating Frog (Rana Cancrivora). J Exp Biol 1 June 1965; 42 (3): 437–445. doi: https://doi.org/10.1242/jeb.42.3.437
The American Naturalist 2011 178:4, 553-558
