Amphibians
Running Frog
Kassina · also called running frogs
A running frog breaks the one rule almost every other frog follows: it does not hop. Instead it walks and runs across the ground on alternating legs, like a small lizard, a gait shared by only a handful of frogs anywhere in the world. It can also inflate its lungs to adjust how it floats, holding perfectly still at a pond’s surface while it calls.
Overview
Running frogs are the genus Kassina, about 14 species of slim, long-legged frogs across the savanna, woodland, and wetlands of sub-Saharan Africa. They hunt ants, termites, and other small invertebrates at night, moving with a distinctive walking or running gait rather than the hop typical of nearly every other frog.
A float built in
Several species can inflate their lungs like a swim bladder to control buoyancy, letting a calling male sit almost motionless at the surface with just his head showing. Males give a range of clicks, whistles, and bell-like notes, and breeding is triggered by seasonal rain filling temporary pans and flooded grassland, with eggs and tadpoles racing to finish development before the water disappears.
Status
Least Concern — widespread and tolerant of disturbed and farmed landscapes as long as some seasonal wetland remains for breeding, with no broad decline documented across the genus.
Running Frog: common questions
Why do running frogs walk instead of hop?
The exact evolutionary advantage is not fully settled, but a walking or running gait, moving the legs alternately rather than pushing off together, may suit a frog that spends a lot of time moving deliberately through grass and low vegetation on the ground rather than making short, quick hops between cover, since it can be more energy-efficient for sustained movement and may make the frog less conspicuous by avoiding the sudden jerky motion of a hop. This alternating-leg gait is rare among frogs generally, found in only a handful of unrelated genera worldwide, making it a striking example of a different locomotor solution evolving independently in a group otherwise defined by hopping.
How does a running frog control its buoyancy in water?
Several running frog species can adjust the volume of air in their lungs, effectively acting like a fish's swim bladder, to control how much of the body floats and how high it sits at the surface. This lets a calling male hold a stable position at the surface of a pond with minimal effort and with just its head or throat exposed, rather than having to actively swim or cling to a support, and it may also help the frog control its depth or exposure when trying to stay hidden from predators while remaining able to breathe air.
Where do running frogs live and breed?
Running frogs are found across the savanna, woodland, and wetland regions of sub-Saharan Africa, generally favouring open or lightly wooded country rather than closed rainforest. They breed mainly in temporary or seasonal water, such as pans, ditches, and flooded grassland that fill after seasonal rains, with large choruses of calling males gathering quickly once suitable water appears, and their eggs and tadpoles are adapted to develop fast enough to complete metamorphosis before that temporary water dries up again.
Are running frogs closely related to reed frogs?
They are both African frogs often found in similar wetland and grassland habitats and are sometimes confused because of overlapping range and general size, but running frogs, genus Kassina, and reed frogs, genus Hyperolius and relatives, belong to different families within the broader group of African tree frog relatives, and running frogs are set apart specifically by their walking and running gait, which reed frogs, being typical hoppers and climbers, do not share.