The Nutrient Cycle - Soil: Reflections on the Basis of our Existence - page 93

My second visit, another hour later, revealed nothing new and when, after four
hours' observation, the only progress was the presence of a few large cockroaches, I
started to feel relieved I had not told my companions of my impromptu scientific probe.
Darkness falls quickly in the rainforest and you scarcely have time to register
that the light is fading before pitch blackness descends. I decided to make a final
visit to the dung heap and entered the forest with a torch. As I walked I heard
male tree frogs calling to attract a mate. The frogs sit high up in the canopy, where
females lay their eggs in the water-filled rosettes of bromeliads. When the tadpoles
become frogs they crawl out into the foliage in search of pools of their own.
At my feet, tiny fluorescent spots shone on the ground when I turned off my
torch, reminding me of old-fashioned light switches that glow so you can find
them in the dark. Carefully trying to avoid touching a bullet ant or, even worse,
a poisonous spider, I rummaged around trying to find out what they were. Earlier
that day, Meyer had pointed out a spider with a bite that can kill a man in three
minutes. Eventually my fingers located something, and when I turned on the torch
I saw it was a leaf—a leaf illuminated by florescent fungal mycelia. Why this par-
ticular fungus has developed an ability to shine in the dark is not known.
On reaching my vantage point I shone the torch on the dung heap and saw that
there was activity at last. Dung beetles were working hard to turn my faeces into
balls that they then rolled by kicking with their hind legs, like squirrels on a tread-
mill, while keeping their other legs on the ground. Balls of dung were being rolled
left and right, and after a few metres negotiating leaves and twigs the beetles
would start burying them in readiness for female dung beetles to enter the scene.
Males who lay the most and largest balls have the greatest chance of fertilising the
eggs that the female lays inside them. After fertilisation, females remain behind to
tend the balls, turning them regularly to prevent mould from forming, while the
males amble off in search of new dung deposits. More than fifty species of dung
beetle have been found in human dung in jungle environments according to
Tropical Nature , and I had seen just a fraction of these on my pile. When, the fol-
lowing morning, I took my colleagues to see the experiment, there was no sign of
either dung or beetles. But I contented myself with the knowledge that my pres-
ence had given the local insects a helping hand—for a few days at least.
The Swedish biologist and author Fredrik Sjöberg has a special interest in dung
beetles and in his anthology of essays Den utbrände kronofogden som fann lyckan
(“The Burned Out Debt Collector Who Found Happiness”), he describes a case from
Australia that highlights the vital role insects play in the ecosystem. When European
colonists settled in Australia, they brought with them cattle from home for beef farm-
ing. However, the indigenous dung beetles ignored the alien dung, which was left to
collect in the fields and became a magnet for the larvae of biting insects. The insects
reached plague proportions, rendering vast areas of land useless for livestock farming.
Farmers responded in the mid-twentieth century with a novel experiment: importing
dung beetles from Europe and Africa. The gambit proved successful and the cycle of
dung production and decomposition now functions well in the Australian outback.
Dung plays host to all sorts of interesting biological phenomena. When teach-
ing a distance course in microbial ecology, I tasked my students with studying