Amphibians
Eastern Banjo Frog
Limnodynastes dumerilii · also called eastern banjo frog, pobblebonk, four-bob frog
The eastern banjo frog is a stout, burrowing frog of southeastern Australia, and it is far more often heard than seen. Its call is a single deep, twanging “bonk” — exactly like a plucked banjo string — and when a whole pond of males calls together, slightly out of step, the burbling result gives the frog its other name: pobblebonk.
Overview
Eastern banjo frogs live across southeastern Australia, in woodland, grassland, heath, farmland, and suburbs, anywhere with still water nearby. They are 5–8.5 cm long, robust and rounded, mottled olive and brown with a pale side-stripe and a bright yellow or orange flash in the groin and thighs.
The call
Males give one short, sharp, resonant note. It carries a long way, and a chorus of males calling out of time produces the rolling, plunking sound the frog is named for. They call from the water’s edge, often partly hidden.
Life underground
The frog digs itself backwards into soft soil using spade-like bumps on its hind feet, and waits out dry spells buried for weeks or months, emerging to feed and breed when rain softens the ground.
Breeding
The female whips mucus and air into a floating foam raft at the surface and lays her eggs inside it, keeping them moist, oxygenated, and hidden. The tadpoles are large — up to 6–8 cm — and can take many months, sometimes over a year, to develop.
Defence
Grabbed, the frog exudes a thick, sticky, milky secretion that tastes foul and can gum up a snake’s mouth or a bird’s bill. It is harmless to people.
Status
The eastern banjo frog is Least Concern, common, and tolerant of farm dams and suburban ponds.
Eastern Banjo Frog: common questions
Why is it called a banjo frog or pobblebonk?
Both names come from the call. A male eastern banjo frog produces a single short, deep, twanging note that sounds remarkably like someone plucking one string of a banjo, so banjo frog is a straightforward description. Pobblebonk is an onomatopoeic name that captures what a whole chorus sounds like. When many males call from a pond, each slightly out of time with the others, the overlapping bonk notes run together into a burbling, plunking rhythm, and pobblebonk imitates that collective sound. The name four-bob frog comes from the same idea, an old rendering of the call as the phrase four bob.
How does the eastern banjo frog survive dry weather?
It goes underground. Using hardened, spade-shaped bumps on its hind feet, the frog shuffles backwards into soft soil, drawing the earth over itself until it is completely buried. There it sits in a chamber, greatly slowing its metabolism and losing very little water, and it can remain like this through weeks or months of dry conditions. When heavy rain finally soaks the ground, the frog digs its way back to the surface to feed and, if conditions are right, to breed. This burrowing habit lets the species live in areas that are dry for much of the year and only briefly wet.
What is the foam nest for?
The floating foam raft protects the eggs during their most vulnerable stage. The female creates it by paddling her forearms to whip her egg-laying fluid together with air into a stiff meringue-like mass at the pond surface. Inside the foam the eggs stay damp even if the surface dries and forms a crust, they are held near the oxygen-rich surface, and they are largely hidden from fish and aquatic insects that would eat exposed eggs. As the embryos develop, the foam gradually breaks down and the hatching tadpoles are released into the water below to continue growing.
Is the eastern banjo frog poisonous?
It is not dangerous to humans, but it is chemically defended. Glands in its skin, particularly along the back and around the parotoid region behind the head, can release a thick, sticky, milky secretion when the frog is grabbed. The fluid tastes foul and is an irritant, and its stickiness can physically foul the mouthparts of a predator such as a snake, giving the frog a chance to escape or making the attacker spit it out. Handling one is harmless as long as you wash your hands afterwards and avoid touching your eyes or mouth.