Most frogs are either nocturnal or crepuscular and are most active in the dark and twilight hours. When inactive, may frogs will burrow is soft soil or mud. But have you ever wondered why frogs burrow?
Frogs burrow for a variety of reasons, such as to cool off or stay warm, to hide from predators, to hibernate, and to ambush prey.
Many species of burrowing frogs have hardened knobs on their back legs which they use to dig themselves backwards down into the ground.
That said, it’s important to note that not all frog species have the ability to burrow.
Many tree frogs can not burrow at all, and will instead retreat to tree hollows and other cool, hidden locations in their habitat.
Frogs Burrow to Escape the Heat or Cold
Like all amphibians, frogs are ectothermic or “cold-blooded” animals. This means that frogs cannot generate their own body heat, so their body temperatures are close to the temperature of their environment.
In other words, their environment is the main influence on their body temperature.
For example, a frog swimming in 30°C (86°F) water has a body temperature very close to 30°C. In 15°C (59°F) water, the body temperature of the same frog is around 15°C.
This is in contrast to endothermic (warm-blooded) animals, like humans whose bodies can generate their own internal heat through their metabolism.
Being ectothermic means that frogs will have a reduced metabolism at lower temperatures, and can go long periods without food. However, it also means that they are more lethargic, and become less active.
Due to being cold-blooded, frogs are very vulnerable to temperature extremes.
If the temperature rises above a certain point, a frog can overheat and be killed or injured.
On the opposite end, If the temperatures drop too low, a frog can be harmed.
For this reason, many frogs burrow in soft soils or mulch to escape extreme temperatures and only emerge when the conditions are more favorable.
While burrowed, some frogs change their body positions to adjust heat exchange via conduction and radiation.
Frogs Burrow to Hide From Predators
Frogs are fairly small creatures and are preyed on by many animals, such as birds, snakes, certain, small mammals, fish, and even large spiders.
For this reason, frogs have developed many ways to defend themselves against predators.
Depending on the species, frogs may rely on camouflage, toxic skin secretions, mimicry, and other tactics to ward off predators.
Some terrestrial frogs may also burrow in to go unnoticed by predators.
Semi-aquatic frogs on the other hand often leap into the water and dive to the bottom to hide from predators.
Frogs Burrow to Ambush Prey
Frogs are generally not fast-moving creatures. This means they can not actively chase after prey as some other predators do. Instead, they wait for the prey to come to them, by using a passive ‘sit and wait’ hunting strategy.
This is an ambush-style technique where the frog hides in shady areas or burrows slightly in the mud and then pounce on any prey that passes by.
Frogs have sticky tongues that allow them to catch any moving insect that comes into range quickly.
Once a frog spots an insect, it launches its tongue to catch the prey. After catching the prey, the tongue wraps around it and coats it with sticky saliva.
The frog will then yank its tongue back with a force equal to twelve times greater than the force of gravity.
Once the insect is in the mouth, the frog will swallow it whole (although frogs have teeth, they do not use them to chew, but rather to maintain a grip on their prey as they swallow it whole).
A frog can shoot out its tongue, capture an insect, and pull it back into its mouth within 07 seconds; which is five times faster than the human eye can blink. This speed makes it effective at catching even fast-flying insects such as flies.
Frogs Burrow to Hibernate
During the winter, frogs in cold regions hibernate to protect themselves from freezing temperatures.
Many terrestrial frogs will hibernate underground, where the frost does not penetrate.
This could be in natural holes or abandoned mammal burrows that are deep enough that the frost does not penetrate all the way to the bottom.
However, some frogs will dig their own hibernacula (hibernating space).
They use their back legs to ‘knead’ their bodies into the soil, submerging themselves completely until they are below the frost line.
Frogs will die if they freeze, so they need to stay below the frost line all winter.
How deep they dig varies from year to year depending on the temperatures and snow cover.
For example, many toads will burrow anywhere from 6 inches to over 3 feet deep; they tend to stay a couple of inches of the frost line and will move up and down throughout the winter as the frost line changes.
Frogs Burrow to Escape Arid Conditions
Frogs have thin membranous skin that they use to breathe and absorb water.
Due to their permeable skin, frogs are very prone to water loss from the skin, particularly in arid conditions.
During dry periods, some frogs will burrow into the ground to reduce water loss.
Frogs such as the Northern Burrowing frog (Neobatrachus aquilonius) can burrow as deep as 3.9 feet (1.2 meters) to escape the arid conditions.
Once burrowed, frogs may estivate as they wait for the rain to come and the temperatures to drop.
Some frog species even form a cocoon of dead skin cells around their bodies to limit water loss.
Not All Frogs Burrow
While some terrestrial frogs may burrow, not all frog species will burrow.
For example, most arboreal frogs seek cover in trees and other vegetation, rather than borrow on the ground.
Other frogs will hide under logs, in rock crevices, the foundations of old buildings, piles of rubble, and other objects.
If you ever go around turning over large rocks, or logs during the wet season, there’s a chance you could find frogs or salamanders hiding underneath.
Conclusion
Many terrestrial frogs will spend some of their underground. This could be in natural holes or abandoned mammal burrows.
Some frogs will also dig their own burrows.
There are several reasons why frogs burrow, such as to cool off, to hunt, and to hibernate.
However, not all frogs have the tendency to burrow, and some frogs will never burrow at all.
Frogs are found are found in a wide range of habitats, and have adaptations suited for the kind of habitats they live.
Sources:
Reynolds SJ, Christian KA, Tracy CR. The cocoon of the fossorial frog Cyclorana australis functions primarily as a barrier to water exchange with the substrate. Physiol Biochem Zool. 2010 Sep-Oct;83(5):877-84. doi: 10.1086/656218. PMID: 20687829.
Burrowing Frogs: https://backyardbuddies.org.au/backyard-buddies/burrowing-frogs/