It's a lucky day for amphibian enthusiasts at Glen Austin wetlands: The giant bullfrogs of southern Africa are having sex. The mating ritual occurs...

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GLEN AUSTIN, South Africa — It’s a lucky day for amphibian enthusiasts at Glen Austin wetlands: The giant bullfrogs of southern Africa are having sex.

The mating ritual occurs just one day a year, after the first downpour of the Southern Hemisphere summer. The shallows of the wetlands north of Johannesburg become a splashing commotion as bullfrogs attack and toss each other about like pint-size wrestling stars.

The giant bullfrog is no cute little Muppet. When it lunges — and South African frog expert Vincent Carruthers has seen it attack horses — it’s a fearsome sight, squinting and baring the two fanglike front teeth in its gaping, shovel-like jaw.

Right now one giant bullfrog, slightly smaller than a dinner plate, is busily trying to procreate with a female, perhaps a tenth his size. But before the deed can be consummated, another male swaggers up and launches himself in toothy attack.

Orange limbs fly and bullfrog No. 1 almost loses his lady, but manages to clamber back on. Again his rival attacks. And again. And again.

And if the skirmishing doesn’t kill these frogs, man almost surely will: The creatures are endangered by the housing developments multiplying around Johannesburg and Pretoria, wiping out the shallow wetlands that are their breeding grounds.

Paul Fairall, 70, a retired farmer and bullfrog aficionado, has been rescuing the giant frogs for 20 years. He grew up with pet crows and snakes and boxes with lizards and toads in his bedroom, out of bounds for his mother.

He tells of one snake breeder who put a bullfrog in the cage as a meal for the reptile. The bullfrog ate the snake.

Alarmed at how often they got squashed by cars, he took on the role of a one-man frog rescue service two decades back. When he sees a bullfrog by the road, he picks it up and tenderly deposits it on the other side.

“If he’s going in one direction, help him in that direction, don’t try to turn him around. Pick him up and take him across the road,” Fairall advises.

He takes dozens of calls during the early summer rains from people all over Johannesburg who find bullfrogs stranded behind garden walls, in their swimming pools or car parks, trying to get to the wetlands.

He’s bought dozens from township people who had caught the bullfrogs to eat.

The frogs have a boring life, most of the time. Carruthers, the frog expert, says they spend about 11 months burrowed under the soil in a state approaching suspended animation. They secrete fluid that sets around their body in a keratin shell, with two small holes for their nostrils. In a drought, they might stay buried for two years.

When the rain comes, they make their way to their breeding grounds. After mating, females retreat to their burrows, but males stay by the fertilized eggs and the tadpoles, turning their aggression against any predators, greatly increasing the tadpoles’ survival chances.

Most extraordinary of all, says Carruthers, is the bullfrogs’ behavior of herding the tadpoles to safety should their water start to dry up. The frogs dig a channel to lower water and herd the tadpoles down the channel, emitting noises like a motorcycle in a low gear.

The bullfrogs, muddy olive with lurid orange underarms and creamy bellies, can live to 45 years in captivity and theoretically to about 20 years in the wild.

But Caroline Yetman, a doctoral student who has been studying the frogs’ behavior since 2002, says that because of habitat loss, frogs in Midrand (between Johannesburg and Pretoria) were surviving only five years and were significantly smaller than they had been in the early 1990s.

“With all this development, the frogs are getting hit by cars or they’re being trapped behind walls and can’t get to their breeding sites or back to their burrows. They’re just not getting old. You don’t see the big, old bullfrogs around anymore.

“Here in Midrand their days are certainly numbered. I don’t see them surviving here beyond the next 20 years, if it’s that much.”

For Fairall, the most wonderful sight — as good as, if not better than, the mating — is the march of the newly transformed tadpoles-turned-frogs from the wetlands shallows en masse, unless of course they happen to be marching up your driveway. (And yes, they do march, or waddle, rather than hop.)

Last year he got a panicky call from a company whose manager was about to call a pest control firm about a baby bullfrog infestation.

Fairall rushed to find thousands of them swarming across the lawn, clogging drains. He estimates he rescued 4,000 of them.