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Somebody has to clean this mess

June 6, 2013

By Piotr Naskrecki - A friend of mine once compared holding a dung beetle in your hand to kissing a dog on the snout – both feel kind of good, until you think of the last thing they have probably been rubbing against. At least with dogs there is some room for other options, but there is no such ambiguity with the beetles. Still, it is difficult not to be impressed with the incredible forms and colors of these insects, and I had to constantly remind myself to be careful while handling the gorgeous dung beetle specimens that Bruno de Medeiros, a Harvard coleopterist participating in our Cheringoma biodiversity survey, kept bringing for me to photograph. For you see, the best and most effective way to collect these beetles is to lure them with a tasty bait. And there is no better bait than dung of an omnivorous mammal, and none is more omnivorous than a human. Dung beetle specialists have long been searching for the Holy Grail of Scarabaeology – a synthetic bait that attracts a wide variety of species – but, alas, they have not yet found it. And so, Bruno, like an expectant mother, was forced to eat for two (or rather several hundred) in order to produce enough bait to fill the dozens of pitfall traps needed to sample dung beetles at each of our survey’s sites.


Photo: The Green dung beetle (Garreta nitens) is a pretty, diurnal species.


We still don’t know how many species of dung beetles came to Bruno’s carefully baited pitfalls – identifying tiny aphodiines and other cryptic forms will take some time – but in his estimation at least 100 species, perhaps more, are to be expected. This is really good news for the Gorongosa ecosystem. Although the park lost a large proportion of its mammal population during the civil war of 1975-1992 and, consequently, its dung beetles surely must have suffered from the sudden decline in availability of their food resources, all original elements of their fauna are probably still in place. This means that as the large mammals return, and populations of most herbivores already show quickly accelerating growth rates, dung beetles will be able to build up quickly and resume their thankless but invaluable services.


Photo: Bruno de Medeiros with one of the largest dung beetles found in Gorongosa, Pachylomerus femoralis.


Dung beetles are critically important members of savanna communities that dominate Gorongosa, and without them and their waste removal labor the place would quickly sink under layers of dung produced by thousands of mammalian grazers and browsers. Their ability to return nutrients trapped in dung into the soil also supports the positive feedback loop between rapid vegetation growth and herbivory. The ecosystem services provided by dung beetles thus carry actual, calculable monetary value – I am not sure what that value is in Gorongosa, but in the United States the dung removal services by beetles is estimated to save the cattle industry $380 million per year. In Australia dung beetles imported from Africa and other places saved the cattle industry from a total collapse after it became apparent that local insects were not adapted to processing manure of non-native mammal species; New Zealand is also considering a similar move to save itself from an ocean of cattle and sheep dung that threatens to engulf the islands.


Photo: Female Heliocopris sp. taking off, apparently not satisfied with the quality of the dung she found.


But dung beetles are not only useful and pretty, they are also supremely cool – a recent study demonstrated that they are the only insects known to navigate using the position of the Milky Way and other galaxies. Only humans (and possibly a few other animals, but it has never been conclusively proven) use the position of celestial bodies to find their way around.


Photo: Male Heliocopris andersoni, one of the largest and most impressive dung beetles in Africa.


And although I quickly learned that I should hold my breath and discreetly reach for a bottle of hand sanitizer every time Bruno brought me a new specimen, it was always a thrill to see a new animal. The high dung beetle richness we found on the Cheringoma Plateau shows that Gorongosa is well on its way to full recovery, and its cleanup crew is alive and well.


A time lapse movie spanning 10 hours of dung beetle activity, showing what happens to warthog dung in Gorongosa. (Click here for a high quality version of the movie.)


Photo: Plum dung beetles (Anachalcos convexus) do not display sexual dimorphism, and both males and females form dung balls; this species is also often seen feeding on dead insects.


Read more on Piotr’s blog The Smaller Majority