There are a couple of ways to think about a monkey turd. You can look at it as a packet of undigested monkey food, which has passed through a monkey gut and collected a bunch of bacteria in the process. Alternatively, you can look at it, to borrow the phrasing of San Francisco State scientist Jennifer Jacobs and colleagues, as "an ephemeral resource in high demand by many organisms."
One beast's trash is another beast's treasure, and a poo pile in the woods provides food for flies, fungi, and other nutrient seekers. Dung beetles are perhaps the archetypal example of these ecologically important decomposers. Sacred to the ancient Egyptians, these insects eat, nest, or even live in dung pats, sometimes rolling outsized dung balls great distances.
The fundamental challenge facing dung beetles is, unsurprisingly, finding dung. This can be challenging in complex habitats where feces-producing mammals are scarce, such as tropical rain forests. Time is of the essence--arrive late and you might find that another poo pirate has stolen the prize. Success in the shit-eating business requires efficiency in locating the stuff.
Most forest dung beetles scan the understory for droppings, aided by a keen sense of something akin to smell. But a recent paper by Jacobs et al. in the journal Neotropical Entomology describes an entirely different and far more straightforward strategy, the logic of which is as follows. A turd is like a cigarette butt: if it's on the ground, that's only because some asshole dropped it there. If you want to be the first to find it, then just hang out next to the nearest asshole.
Jacobs et al. report this behavior in the dung beetle Canthon aff. quadriguttatus, which they observed "sitting and waiting" around the anal and genital regions of the brown titi and bald-faced saki monkeys. When the monkeys take a dump, the beetles drop to the forest floor and begin rolling the conveniently sized poo pellets away. This ass-riding behavior, called phoresy, has been described in other dung beetles, but the Jacobs paper notes a new case and provides visual evidence in the form of stunning full-color photographs.
At this point, you might be feeling as appalled as the young woman sitting next to us on the airplane as we type this, who keeps glancing sideways at our computer screen, then up at the flight attendants, then back at the computer screen, and who seems ready to reach for the air-sickness bag
any second. So try to see this from the beetle's perspective. You have six tiny feet, a set of wings, and a penchant for poo. Suddenly, you're no longer a puny bug clinging to the hair on a monkey's butt, no sir. Now you're a chocoholic hobo riding the Fudge Train to Fudgetown. Or one of those creepy self-righteous munchkins from Charlie and the Chocolate Factory, living alongside a fudge river as wide and brown as the mighty Mississip.
Other fudge-related metaphors might also be appropriate; we invite you to post them in the comments section.
In any event, this is a winning paper. It's cool evidence for an evolutionarily adaptive strategy
to the classic ecological problem of finding food, but it's also more than that. It's an elegantly written research communication in an era when elegance in formal scientific writing seems to have gone the way of the dodo. In places, it's almost poetic: "From a distance, the beetles attached to the monkeys appeared as jewels or shiny water droplets." Emily Dickinson would be proud (we're not sure what Emily Post would think).
Elsewhere, we hear of a research assistant who "reported that a fecal pellet from a bald-faced saki monkey, with dung beetles attached, fell directly into his shirt pocket as he was observing monkeys in the canopy overhead." Fieldwork doesn't get any better than that, y'all.
As always, new findings raise new questions. Reconstructing the evolutionary history of the beetles, for example, would help us estimate when this behavior evolved, and how many separate times it has arisen in different beetle groups. Someone should get on that. But for now, check out the paper, enjoy the photos, and maybe take a minute to savor the fact that you're not a brown titi monkey. Or a dung beetle.