If you search the word “frog” on the internet, you will likely find a nearly endless number of photos of plump, round frogs.
It seems like many, if not most, frogs are fat. But why is that the case?
Many animals, frogs included, become dormant during colder months. Since they do not eat during this time, fat stores in their bodies are their main source of energy to keep them alive until the weather warms up and they become active again (Wygoda et al. 1987).
Fat frogs may be adorable, but their fat serves a purpose!
As long as a frog is not being intentionally or unintentionally overfed by a human caretaker, being fat is not only okay for frogs, it is in fact critically important.
How Do Frogs Become Fat?
Fat reserves, the storage of fat that causes an animal such as a frog to appear “fat” visually, are accumulated through eating excess food.
Fat is used as energy in place of food when the frog is dormant and therefore not eating. So, by eating more before their brumation, the frogs allow themselves to go without eating during their brumation.
Fat accumulates in an animal’s body when the amount of calories consumed is more than the amount of calories burned.
Therefore, animals that brumate or hibernate, such as frogs, snakes, and bears, must eat very large quantities of food to consume the amount of calories needed to establish sufficient fat deposits.
Some frogs may eat hundreds, or even thousands, of insects to accumulate their fat stores.
Since frogs are opportunistic hunters, any bug that is unfortunate enough to cross a frog’s path is likely to become dinner, and help the frog build the fat stores that will carry it through brumation.
Are Fat Frogs Unhealthy?
Wild frogs may often look “fat” to people viewing them. In reality, the appearance of fatness is caused by fat stores being accumulated to help the frog survive months without eating during brumation.
Typically, a fat wild frog is a healthy frog! A thin frog could potentially be suffering from parasites or some other ailment preventing it from reaching a normal, healthy weight.
Of course, it is possible for diseases, parasites, or other ailments to cause swelling or bloating in wild frogs, creating an appearance of excessive, unnatural fatness, but this will likely look different from a normal, healthy, fat frog.
In captivity, a frog may become overweight to the point of being unhealthy if it is overfed and/or not given sufficient ability to exercise.
Captive frogs will also typically not brumate the way their wild counterparts would, and therefore excess fat stores will typically not be necessary in captive frogs.
That does not mean that pet frogs should be kept thin or allowed to be thin – pet frog keepers should research the optimal body condition for the species they keep and strive to achieve that.
How Is Being Fat Good For Frogs?
When a frog brumates, or becomes dormant during the colder months, they do not hunt or eat. Therefore, the frog needs another form of sustenance.
This is why the frog will have spent the warmer months preceding brumation eating every bug it can catch. The frog will have accumulated fat reserves to keep it healthy through brumation.
Fat reserves are essentially energy storage. Instead of getting energy from the food it eats, a brumating frog gets energy by utilizing the fat storage in its body.
The fat is converted to energy, which allows the frog to remain alive throughout brumation, until it wakes up when the weather warms.
A frog that is dormant needs much less energy than a frog that is active. This allows the fat reserves to last much longer than they would in the case of an active frog that cannot find food and must resort to using its fat storage outside of brumation.
When the frog wakes back up at the end of its brumation, it will look much thinner than it did a few months prior. However, the newly active frog will quickly get to work eating and rebuilding those expended fat storages.
Can A Frog Be Too Fat?
It is important to keep in mind that frogs evolved over millions of years to live in a specific way. Becoming fat naturally to survive brumation is a normal, healthy thing for a frog to experience.
However, it is absolutely possible for a frog to become too fat and overweight. Typically, this will not occur in wild frogs, but is common in captive frogs.
Captive frogs may become too fat due to being given too much food, having too little activity, not brumating due to constant indoors temperatures, or any combination of possibilities.
Many owners over-feed their pet frogs, believing that if a frog keeps eating, it must need more food.
Remember that frogs are opportunistic feeders who are meant to create fat stores for brumation.
A frog in captivity will also typically not brumate, preventing it from utilizing the fat storage it has accumulated.
Frogs in small enclosures may also become overweight due to limited ability to move and burn calories from the food they have eaten.
The proper weight and body condition for a frog vary from species to species, and vary based on age and gender within the same species.
It is critically important for any pet frog owner to do the necessary research to know the proper body condition for a healthy frog.
Learn more about how safe foods and how to keep frogs healthy on our blog.
Wygoda, M. L., Garman, R. H., & Howard, C. E. (1987). Cutaneous and subcutaneous adipose tissue in Anuran amphibians. Copeia, 1987(4), 1031. https://doi.org/10.2307/1445569
Brenner, F. J. (1969). The Role of Temperature and Fat Deposition in Hibernation and Reproduction in Two Species of Frogs. Herpetologica, 25(2), 105–113.