Caverns of darkness

aves Рthe cradles of humankind Рare home to many fascinating creatures highly adapted to their environment. But enter them at your own risk, writes Abr̩ J Steyn.
Issue date 23 January 2009

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Caves – the cradles of humankind – are home to many fascinating creatures highly adapted to their environment. But enter them at your own risk, writes Abré J Steyn.

As my head broke the surface of the water, I could not see a thing. It was pitch black like I’ve never seen before and I knew, then, what it must feel like to be blind. Suddenly the water splashed as my friend Ben also surfaced. He called out to me, but I could not determine his location as the resounding echo of his voice bounced off the cave walls all around us. There was a strange smell and the air was warm and humid.
Feeling disorientated, I wanted to get out of there and return through the hole in the rock wall, through which we had swum. Our torches, being non-waterproof, had been left behind on the other side. I turned around, but could not even find the wall, let alone the hole.
No matter how far I swam, there was just water in front of me. I turned again and eventually swam headlong into a wall. Searching for a long time along it, I failed to find the hole, which was about 1m under the surface. Getting tired, I started to reflect on how stupid we were and how we were going to die in that underground lake, deep in the belly of the earth. As I started to panic, Ben found the hole, waited for me and, holding on to each other, we swam back to the other side, greatly relieved to see the headlamps of the rest of our party again.
What we did was quite irresponsible and dangerous, but we were young, adventurous students at the time on a bat-ringing expedition to one of the many caves in the Makapansgat Valley, north of Potgietersrust. The caves are of great importance, having yielded thousands of fossils dating back as far as 3,3 million years, and providing a record of hominid occupation from before ape-men discovered stone tools and used bone, teeth and horn instead, right through the Stone and Iron Ages, up to the present day. Nowhere else in the world has such an extended and complete record of hominid occupation been found.
However, we were not there to look for fossils, but to ring bats in Ficus Cave, which got its name from the many fig-tree roots curtaining its entrance. It contained a deep subterranean lake, but the steep and dusty way to it had a 45º slope littered with boulders, over which I battled to get with my crutches. The lake’s water was so clear that, with no reflection from the other side, it was invisible and one could easily stumble into it.
However, in the light of our headlamps, we could watch a rock thrown into the water for half-a-minute, until it reached the bottom far below. Ben and I saw small, translucent shrimp-like creatures in the water and went in, trying to collect some, but without the right capturing equipment, we had no success. Then we saw the hole in the wall, decided to investigate and almost became fossils ourselves.
The cave was full of all kinds of life and also home to an enormous colony of millions of migratory long-fingered bats, Miniopterus schreibersii. Starting to fly out at sunset, it took almost an hour for all of them to leave the cave. It was impossible to put up a net in the entrance at dusk, as their sheer weight would tear it to pieces. Instead we caught them during the day inside the cave and ringed them at leisure. They are still there today, but their numbers have been greatly reduced by pesticides.
After my experience of disorientation in the darkness, I greatly respected the wonderful ability of bats to navigate by their thousands through those dark tunnels without colliding into each other. We know that by constantly emitting supersonic clicks, they use echolocation, but that does not explain how they recognise their own clicks among thousands.
Nor do we know how they determine exactly from which direction their own clicks bounce back so as to react in a fraction of a second. Nor how a female bat recognises her baby’s squeak among a million others. These things fill me with speechless wonder.
Bats do not spend all their time in the darkness of caves, but other creatures do. Their eyes are just as useless in darkness as mine were and that’s why they have lost them. There are many totally blind shrimps, crickets, beetles and fish which live permanently in caves and which have lost all pigmentation, leaving them with a pinkish-white, ghost-like appearance.
In the Aigamas Cave near Otavi in Namibia, a critically endangered white cave catfish, Clarias cavernicola, occurs. There are probably less than 150 left. Initially somewhat reduced by aquarists, they’re now severely threatened by the depletion of groundwater in local aquifers, which has caused lake levels in Aigamas Cave to drop by about 20m over the years. They grow to 16cm, have very small eyes, are probably effectively blind and feed largely on bat droppings, which may be good for them but not for us – they caused a potentially fatal sequel to my cave adventure.
Several weeks after our visit to Ficus Cave, both Ben and I fell seriously ill. Medical tests revealed we had been infected by a fungal disease called histoplasmosis, which thrives in dry and dusty bat guano in caves inhabited by Miniopterus schreibersii, as well as in droppings of domestic birds like chickens and other birds which nest around houses. If not treated, this microscopic fungus can be fatal to humans, so, if you do go into a cave, be aware that it can be dangerous. Protect yourself as well as the caves, because, after all, they were the cradles of humanity.
Contact Abré J Steyn on 083 235 4822 or e-mail [email protected].     |fw