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Sunday, December 2, 2001
Nature

They are the creatures of the caves
Nutan Shukla

DEEP in the world’s great cave systems, where light never penetrates, live a variety of animals to whom eyesight has become an irrelevance. These caves, over the eons, have been carved out by streams that wander through them. Water, too, ornamented the chambers inside these enormous caves. Charged with calcium as it seeped through roof over millennia, it created fantastically sculpted stalactites and stalagmites. Most of the larger animals, like cave racer snakes, that live in the dark environment of these underground galaries feed on cave swiftlets that nest and roost here by night and bats who come here for shelter during day.

Cave swiftlets are birds related to swifts, some of which are known for their great speed. Swiftlets are famous for their nest which they construct with their saliva. These nests are the main ingredient of birds’ nest soup, a delicacy in some of the countries of the Far-east.

Journeys in and out of the caves are always fraught with dangers both for swiftlets and the bats. Cave racer snakes take full advantage of rushing in and out by these flying creatures. Waiting on the cave walls, these reptiles are ever ready to pluck a flying-meal from mid-air.

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Fully equipped to navigate in pitch darkness, these snakes follow well-worn, rippled ribbons of polished bat-guano (bat excrement) into the deep recesses of the caves, and can climb the walls to reach bird nests, where they prey upon eggs and chicks too. More unexpectedly, they coil around stalactites, stalagmites and rocky projections at narrow points in the cave passages, places where traffic flow is restricted and flying animals must slow their flight. The snakes hang out into the void with mouths agape and snatch at anything that comes close. It is thought that air-pressure waves from the flapping wings are detected by the snakes, although the snakes have also been heard to make mewing sounds — an unusual thing for a snake to do—which might have something to do with echolocation, a common way in which cave animals find prey.

The caves are also home to hunting spiders, which, like many other troglodytes, are blind. They run about with their first pair of legs, which are covered with sensory hairs, held out in front like antennae. With these, they can detect the movements of the smaller cave crickets.

The cave crickets themselves grow to monstrous proportions, and one of the most spectacular predators is a giant with huge legs and muscular jaws that can tear a cave swiftlet chick apart, even in the nest high above the cavefloor. One specimen has been seen to take a swiftlet egg in its jaws and smash it against the rock and eat it.

In the cave streams that gouge rills and ridges between the bat dung, cave crabs and gaint toads battle for injured fledglings. Two crabs might tear a chick in half. A related species, deep in the caves, has lost all pigment, has reduced eyes and possesses long legs with which it can crawl about the caveslike an amphibious spider. Long-legged centipedes, multi-legged cave earwigs and shimmering golden cockroaches complete the horrible picture.

Outside the entrances of the caves are patrolled by bat hawks, dark peregrine-sized raptors that take advantage of the comings and goings at dawn and dusk. They, too, wait and watch, placing themselves at a point of plenty, ready to take advantage of the superabundance of prey. At dawn, the swiftlets leave en masse to feed by day and the bats return to roost. At dusk, it is the reverse, and the bat hawks are ready to pounce. They swoop in at an angle across the cave mouth and tear through the emerging and returning flocks. Every morning and evening there is a pandemonium as bats and swifts, both pursued by hawks, change shifts. At twilight, the bats stream out and the swiftlets, diving a spiral from a great height to avoid the waiting predators, fly in.

If it were not for the bats and the birds, this remarkable community would not exist. They collect from the surrounding forest and provide enough food to support a cave floor fauna that is most likely larger than that on the floor of the forest itself.

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This feature was published on November 25, 2001
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