Gauteng’s elusive giant bullfrogs, which lurk underground for most of the year, have emerged in their numbers in Heidelberg, southeast of Johannesburg, after days of heavy rains.
Bullfrogs often emerge if more than 20mm of rain has fallen over three days or more, which creates marshy conditions in shallow water that are ideal for breeding, North West University environmental sciences and management professor Ché Weldon explained.
Weldon said bullfrogs only breed once or twice a year, between December and January, and are selective in their breeding, only doing so when weather conditions are right.
But the reason we often do not see this phenomenon is because they bury themselves, up to 20cm, below the soil’s surface, a few hundred metres away from breeding sites, researcher Caroline Yetman found.
Here, they lay dormant, sometimes for 11 months at a time.
Endangered Wildlife Trust threatened amphibian programme manager Dr Jeanne Tarrant said bullfrogs are “explosive breeders”.
Although not a rare event for the species in the past, rapidly declining numbers make such sights all the more special.
The Heidelberg SPCA, and many residents, have been snapping up pictures of frolicking frogs over the past few days, with many saying the soothing croaks are a welcome sound.
They, however, warned people to refrain from disturbing the frogs, who are hard at work, breeding up a storm.
Due to their lazy lifestyle, areas teeming with giant bullfrogs are often misidentified during construction ventures as not having any wildlife to pay attention to during conventional surveys, the North West University found in a research paper exploring using sniffer dogs to help with amphibian conservation.
This, combined with the lack of monitoring of giant bullfrogs, makes this species particularly vulnerable.
“We simply cannot keep placing so little value in intact ecosystems while viewing destruction of these habitats as ‘progress’ or ‘development’,” Tarrant said.
Pyxicephalus adspersus is a protected species that is currently threatened due to habitat loss as a result of land development. Infectious disease is also adding to the giant bullfrog’s woes.
They also migrate between ponds or wetlands, and are often killed while crossing busy highways.
Sewage and pollution also contributes to dwindling bullfrog numbers.
Weldon said due to Giant Bullfrogs’ wide distribution, they are listed as Least Concern by the IUCN red list.
But due to the limited areas where they thrive, they are “unofficially regarded as threatened”.
“Having one locality undisturbed, but the adjacent one destroyed could be detrimental to that particular frog population,” Weldon explained.
Tarrant said the Gauteng Department of Agriculture and Rural Development also considers the Giant Bullfrog as a Species of Concern.
These frogs are found across South Africa, from Diepsloot to Viljoenskroon, as well as in Zimbabwe, Botswana and Zambia. Waldon said they tend to stick to areas with sandy soils with seasonal lakes or ponds.
Residents have a big part to play in raising awareness when it comes to the presence of these underground amphibians.
In Heidelberg, for example, Tarrant said residents have cordoned off areas when they are breeding.
Male giant bullfrogs are particularly aggressive during mating periods, and have known to give humans a nasty bite.
They will attack anything threatening their eggs or tadpoles, which they guard for the 30 days it takes for eggs to turn into froglets.
Male bullfrogs also dig channels through the shallow mud pans, to make sure that tadpoles stay in the water to complete their development, Tarrant explained.
Bullfrogs reportedly eat anything from a fly to a small chicken, and tadpoles, froglets and adults have known to be cannibalistic – but only when there is a high population density, or when there is very little food available.
If you are lucky enough to find a giant bullfrog in your garden, it is best left alone. It eats nasty bugs and is not poisonous.
But if you must move it, for fear it will be attacked by a pet or run over by cars, Yetman suggests catching the frog, placing it in a bucket with 1cm of water, and relocating it to the biggest veld area you can find, no more than 10km from where you originally found it.