17 Jul Giant bullfrogs
Imagine a predator that can weigh over two kilograms, spends most of the year underground cocooned in layers of dry skin but emerges after heavy rain to breed, and then carefully looks after its babies when they hatch but occasionally resorts to eating the selfsame offspring?
It sounds like something from a sci-fi tale but it is not, it is a male Giant bullfrog.
Giant Bullfrogs occur in many parts of southern Africa including South Africa, Zimbabwe, Botswana and Namibia. There are two species – the Giant bullfrog, Pyxicephalus adspersus, and the Bushveld bullfrog, Pyxicephalus edulis, but they are difficult to tell apart and herpetologists have to rely on their calls and breeding behaviour to differentiate between the two.
Bullfrogs spend most of the year underground, where possible they use the same burrow year after year, wrapped in a cocoon of dead skin that helps prevent them from drying out before emerging at the start of the rainy season, usually late October or early November, to breed in shallow pans of water.
The males, which are bigger than the females, are very aggressive during the mating period, fighting with anything they believe to be a threat to their breeding success. This includes humans and many a person has backed away in surprise when attacked by one of these intimidating frogs.
Once the frogs have bred, territorial males are larger than non-territorial males and try to select the females they want, the newly hatched tadpoles are looked after by the frog that dominates the territory.
They are ferocious in the defence of the tadpoles and also use their hind legs to create channels that allow the tadpoles to get to deeper water if it appears they are being isolated. Unfortunately, if food is scarce, the bullfrog may decide to eat the tadpoles he has so carefully nurtured. The tadpoles take about 30 days to mature into “froglets”.
The females usually avoid contact with territorial males unless mating. Smaller males also steer clear because fights can sometimes result in death and researchers report that many of the bigger males carry scars from fights.
Giant bullfrogs kill and eat anything they can catch including insects, reptiles, other amphibians and small rodents. Researcher Caroline Yetman noted that “Bullfrogs eat any animal ranging in size between a fly and a small chicken.” And their own tadpoles.
Giant bullfrogs themselves are eaten by birds such as herons.
In Limpopo Province in South Africa and other parts of Africa they are considered to be a delicacy and in some are sold at informal butcher shops.
Urbanisation poses a major threat to the giant bullfrogs and the shallow pans essential to their breeding cycle are often drained to allow the building of housing, shopping centres and industrial complexes.