Mystery of the legless frogs is solved

THREE cheers for the farmer I saw pulling ragwort in a sloping field, just south-west of Bandon.

Three cheers, too, for the dozens of cinnabar moths and the hundred of their black-and-amber caterpillars I saw in the dunes at Inchydoney, stripping the ragwort to the bone. It looks nice now, with its bright yellow flowers, but in a month’s time it will look like a miniature forest after a nuclear bomb. It feeds bumble bees, and red soldier insects like to copulate on it, but it is lethal if inadvertently cut-and-dried with hay, and fed to horses.

A correspondent tells me that she and a colleague spend their lunchtime, cameras in hand, chasing damselflies near her Dublin workplace, in East Point Business Park.

“Some of the younger people in the park were rather amused at us lying in the grass, and me wading into a pond (office skirt hitched up totally unprofessional but happy!). One bright spark said ‘Oh, look they’re chasing frogs!’ Well, it’s another good reason for occasionally wearing ‘crocs’ to work, say I!” And it also goes to show how even city lunch breaks can be replete with joys of discovery and visions of shimmering creatures. As the Good Book says, “They do not labour or spin.

Yet I tell you that not even Solomon in all his splendour was dressed like one of these.” I believe the reference was to the lilies of the field, but for sheer dazzling apparel, one could hardly better damselflies.

The same correspondent directed me to research aired on a BBC news bulletin, which highlighted a less attractive aspect of the ‘shimmering creatures’ or, at least of their cousins, the dragonflies. Scientists have found them responsible for the curious case of the missing frogs’ legs. Around the world, frogs are found with missing or misshapen limbs. The mystery became one of the most contentious environmental issues of all time.

Many researchers believed it was caused by chemical pollution, or UV-B radiation caused by the thinning of the ozone layer.

Tests have revealed that the deformed frogs are victims of the predatory habits of dragonfly nymphs, which eat the legs of tadpoles. The mystery was solved when Professor Stanley Sessions, an amphibian specialist at Hartwick College, in Oneonta, New York, teamed up with Professor Brandon Ballengee, of the University of Plymouth, UK. For a decade, they collaborated and spent the summers of 2006 to 2008 surveying the occurrence of deformities in wild amphibians at three Yorkshire ponds.

They were surprised to find so many metamorphic toads with abnormal limbs, as it was thought to be a North American phenomenon.

A range of natural predators was investigated, including stickleback fish, newts, diving beetles, water scorpions and predatory dragonfly nymphs.

They tested how each predator preyed upon the tadpoles, by placing them together in fish tanks in the lab. None did, except three species of dragonfly nymph.

The nymphs rarely ate the tadpoles whole.

They would grab the tadpole and chew at a hind limb, often removing it altogether. Remarkably, many tadpoles survive this ordeal.

If attacked when very young, they often regenerate their leg completely, but this ability diminishes as they grow older. Adult amphibians with one hind limb appear able to live for quite a long time, explaining why so many deformed frogs and toads are discovered. So, it would seem the case of the unfortunate legless frogs has been solved.

But now, for another natural history puzzler. One sunny Sunday, watching the lazy meandering of three basking sharks in the bay in front of his coastal home, in west Cork, my pal, Peter (recently called to the Bar), thought one shark was in trouble. It had stopped moving.

Knowing that sharks must keep swimming all the time or they drown, he began to think that it had gone to sleep.

He suggested to his female companion that he should go and wake it up. He was starting to don his swimming gear when his girlfriend says, “Peter, it is called a basking shark. Presumably it is, simply, basking…” And, indeed, it was. Five minutes later, it flicked its giant tail and moved on. But the question arises: is it entirely true that sharks must keep moving or they drown?