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OPINIONS

From Soil to Stars

Last Friday night, I treated myself to a moonlit walk on Ocean Beach. The atmosphere is amazingly clear in western San Francisco at this time of year (warmer weather brings daily fog and cloud cover), so even with a full moon and the glow of San Francisco’s night lights, the sky was liberally sprinkled with stars.

Although light pollution obscured the Milky Way, I was reminded of many similarly clear nights at sea, in the mountains, and especially in New Zealand, when the striking band of our galaxy arced gracefully across the night sky.

Of course, there are reasons besides pleasure to look up at the night sky. I come from a seafaring family, so the importance of stars to navigation has never escaped me. And we are hardly a unique species in our use of celestial beacons: honeybees use the sun, our closest star, as their guide; many migratory birds use the sun by day and stars by night to stay on track.

Last week, while I wandered the beach aimlessly, scientists added yet another animal to the stargazing ranks, this one from the humblest of lifestyles. The dung beetle, sewage treatment plant of the natural world, apparently looks to the Milky Way for guidance as it rolls its dung balls across the darkened landscape.

Alternately revered (the ancient Egyptians considered scarabs sacred) and eschewed (their lifestyle makes many squeamish), dung beetles nonetheless play a critical role in most terrestrial ecosystems because they specialize in processing, well, dung. They are particularly fond of herbivore waste, siphoning off the remaining nutrients and apportioning segments to feed their young. Some species roll up neat little balls of dung and wheel them off to new locales, others bury their findings nearby and a few just add their eggs to the top of the pile. But regardless of method, the dung beetle is crucial to both the dispersal of this waste and the redistribution and recycling of the nutrients hidden inside.

The beetles are so active, in fact, that they’re credited with doing $380 million in behind-the-scenes work for the United States cattle industry, whose meaty members produce up to a dozen dung piles each day. In some places, like Texas, dung beetles bury up to 80% of this waste, turning cowpats that would harden into smelly, grass-stunting lumps into tiny packets of fertilizer. And since every dung pile can spawn 3,000 flies, the beetles provide a big pest control service as well.

Dung beetles are found all over the world, their distributions mirroring that of mammals. Across the planet, they’ve adapted to deserts, mountains, and even tropical jungles, specializing on whatever fecal matter is available.

But in some areas where the mammals on which they depend are in decline, dung beetles are disappearing too. In many parts of the tropics, the bushmeat trade and subsistence hunting are dramatically reducing herbivore populations. Without fecal food and housing, dung beetle numbers are following suit, changing the nutrient cycling pathways of entire ecosystems.

In this regard, we North Americans have been lucky: Our dung beetles probably once made their living on bison droppings, making them particularly well-suited for cleaning up after the cows we’ve used to repopulate the plains.

In other parts of the world, though, animal husbandry has struggled to make a match with the local beetle brigade. Australia, for example, has several hundred native species of dung beetle, but none were up to the task of processing waste from its imported cattle industry. In an effort to clear pastures and suppress huge swarms of bush-flies, the Aussies have introduced 43 different species of dung beetle over the last 55 years, and are planning to add a French beetle to round out their cleanup crew.

In New Zealand, too, where the dairy industry has recently become the economic darling, scientists are auditioning dung beetles for possible introduction. Bringing any new species to the island nation poses risks, so the insects have to be quarantined and rigorously tested to avoid accidentally importing a disease or producing unexpected ecological side effects.

Having narrowly sidestepped many a dung pile during research and exploration in New Zealand, I’m sure that, should dung beetles be introduced to the country, the differences will be marked. And then, while wandering around at night with my gaze lifted to the Milky Way-lit sky, I will be in good navigational company – and won’t need to watch my step.

Holly welcomes questions, comments, and tips on celestial navigation via email at hollyvm@stanford.edu.

About Holly Moeller

Holly is a Ph.D. student in Ecology and Evolution, with interests that range from marine microbes to trees and mushrooms to the future of human life on this swiftly tilting planet. She's been writing "Seeing Green" since 2007, and still hasn't run out of environmental issues to cover, so to stay sane she goes for long runs, communes with redwood trees and does yoga (badly).