Photograph by Yannick Lowery
words by jason p. dinh
Guided by celestial bodies in the sky, dung beetles fertilize the land, nourishing their surroundings and engineering flourishing ecosystems.
For insects, dung is pretty close to ambrosia—the nectar of the gods—according to Dr. Doug Emlen.
“If you’re a larval stage insect, pretty much all you’re doing is eating and growing,” said Emlen, an evolutionary biologist at the University of Montana. Building proteins and tissue requires nitrogen, which scat is brimming with. Feces are far more nutritious than leaves, which are mostly fibers and starches, or sap, which is mostly water.
That’s why some insects—most famously, dung beetles, which belong to the larger family of scarab beetles—have specialized on scat to feed their young. Ranging in size from half a grain of rice to a tennis ball, dung beetles can home in on the smell of a freshly laid pat in mere minutes, and competition is fierce. Emlen recalled one particularly riotous elephant dung in the Serengeti: “We probably had 100,000 beetles come in. It was just pouring down our shirts… It was like a hailstorm.”
Like the cornucopia in The Hunger Games, it’s a free for all, each beetle grabbing what they can and booking it. Of the more than 7,000 species of dung beetles, a subset, called rollers, carve balls of stool and beeline away from the melee before burying it. Others, called tunnelers, burrow beneath the scat and cache their bounty directly below the action.
The adults consume the liquid portion of feces, but it’s mostly for their young. Once dung is secured, beetles lay their eggs directly into the stool, rationing out meals for when the larvae hatch.
For insects, dung is pretty close to ambrosia—the nectar of the gods.
Dung beetles have, in desperate pursuit of an overlooked resource, adorned themselves with magnificent traits—exquisite senses of smell and powerful flight muscles used to scan for freshly laid pats, a celestial compass that rollers use to maintain pin-straight bearings, and massive horns that tunnelers wield to defend their nests. They also engineer their surrounding ecosystems. They decompose and disperse scat, fertilizing the soil they roll over and dig into, and structuring the topsoil to allow plants and the animals that rely on them to thrive. Dung beetles convert discarded bodily waste into diversity, both for themselves and their surroundings.
Ancient Egyptians believed that these humble insects were earthly manifestations of the sun’s daily journey. Khepri, the scarab-headed god, rolled the sun across the sky, burying it under the horizon each evening. Like newly metamorphosed adult dung beetles, which seem to spontaneously emerge from the ground, the sun, too, rises each morning. That’s why, in addition to the sun, Khepri was associated with creation and rebirth—and why ancient Egyptians fashioned scarab amulets as totems of good fortune to accompany the deceased into the afterlife.
Perhaps beetles don’t roll the sun around the Earth, and they don’t spontaneously reproduce like the ancient Egyptians believed. But there is some truth to the tale. Navigating using the sky, they wield celestial powers. And, for their hard work tending to the land, they give the gift of life, presenting harbingers of good fortune when they are present—and omens of collapse if they disappear.
From Soil to the Stars
If you visited South Africa’s Johannesburg planetarium in 2009, you might have smelled a sour scent.
Each night after the planetarium’s regular shows, Dr. Marie Dacke, a sensory biologist at Lund University in Sweden, arrived with a team of scientists—and a horde of dung beetles.
“This wasn’t planned. We called them: Can we please come and use the planetarium? We need to manipulate the starry sky,” said Dacke. “The planetarium did have an interesting smell for the time when we were there, even during the day, but [the staff] were quite enthusiastic.”
Their creative, albeit unusual, experiment tested how dung beetles roll balls in such straight lines. Brood balls can make up to 79 times a roller’s body weight. They push them using their hindlegs, planting their face into the ground. Like a child’s illustration of the sun, their paths veer out in all directions from the central pat, but once an individual chooses a bearing, it maintains it the entire way, regardless of the obstacles in its path. Their unswerving nature is paramount to escaping their rivals who are on the prowl to steal their food, Dacke said.
Dacke and her colleagues previously showed that rollers keep a straight path by orienting to the sky. Species that are active during the day cue into the sun as well as patterns of color and intensity; nocturnal species use the polarized light cast by the moon, a pattern that humans can’t see. “I often explain it as light vibrating in circular patterns around the moon or the sun,” with the actual celestial body at the center, Dacke said.
The researchers headed to the planetarium to test if beetles used another celestial compass: the Milky Way. Earlier in the field season, they noticed that beetles could steer straight even on a moonless night, but they lost their way when it was overcast. There must be something aside from the moon in the sky that clouds are covering, they figured. It probably wasn’t individual stars—those aren’t bright enough for them to see—but maybe, the Milky Way is.
By finding value in waste, dung beetles have conjured a fascinating adaptation for everyone.
So, off to the planetarium they went. Releasing beetles into a circular, sand-filled arena, they allowed them to roam under the moonless 18-meter dome without its brightest stars, without the Milky Way, and without any visual cues whatsoever. And behold: The beetles best maintained a straight bearing when the Milky Way was projected. The insects, the researchers wrote in their 2013 paper in the journal Current Biology, were the first animals known to orient themselves using the galactic band.
Emlen is fascinated by the behavior—but given the diversity of dung beetles, it doesn’t tell the entire tale. Tunnelers, without the glitz and glamor, don’t roll dung and don’t have sophisticated ways to flee. Instead, they fight, with many using elaborate horns as weapons.
Horns, Emlen said, can be on the back of their heads, top of their heads, and the equivalent of their shoulder blades. Larger weapons provide a combative edge in tunnels where battles are predictable, head-to-head, and one-on-one. Beetles can use them to anchor into the dirt and block the entryway, and they can pry their opponents loose to evict them. The push-and-shove fights have even led one beetle, Onthophagus taurus, to be able to pull 1,141 times its body weight—by some metrics, the strongest known insect.
That advantage is significant in a tunnel, but not so much in the scramble between rolling beetles, Emlen said. In the open air, beetles might get charged from the side or face multiple opponents simultaneously. The battles are chaotic. Combatants tussle, cling, and even tear apart their dung balls.
“It’s wildly stochastic,” he said. “It’s not cost effective to produce a weapon because you’re not going to be able to use a weapon.” Of the thousands of ball-rolling species, Emlen wrote in his 2014 book Animal Weapons, not a single one has large horns.
“Even Darwin was on to the fact that there’s something special about scarab beetles. They just have an incredible diversity of forms,” Emlen said. And whether you’re Team Weapon or Team Compass, by finding value in waste, dung beetles have conjured a fascinating adaptation for everyone.
Engineering from Excrement
Farmer Mike Hansen was thrilled when he discovered there were dung beetles on his land.
The 55-year-old started Ozark Akerz Regenerative Farm just nine years ago. When asked why, he gave a terse answer: “cancer.”
In 2002, his six-year-old son was diagnosed with terminal spinal cord cancer. He was told he had three months to live (he survived, these days living in Denmark as a champion wheelchair basketball player). Then, in 2005, his wife Sue was diagnosed with cancer.
“The treatment—it practically killed her,” he told me. Over the next five or six years, Sue struggled to find food that was flavorful and nutritious enough to support her recovery. Perhaps, they thought, they could grow it themselves. “In 2014, we left our jobs, and kind of bet everything on ourselves to start a farm,” Hansen said.
Located in Coleridge, North Carolina, their regenerative farm is an ecosystem that has over 600 documented species, including native plants, native crops, milkweed stands for monarch butterflies, chickens, and pineywoods cattle. Here, Hansen said, every species affects the wellbeing of the other. And to their delight, that includes dung beetles.
“We really started noticing them because the cowpats would just disappear into the earth,” Hansen said. “We didn’t introduce them. It was a natural population that was already here.”
Most of the species that live in North Carolina are diminutive tunnelers, he said. “They take that dung down into the pasture and fertilize it for us.” That aerates the soil, allows water to penetrate, and fertilizes their land so they don’t have to purchase nitrogen fertilizers. “I think we were saving ourselves about $2,000 per year,” he said.
Dung decomposition is the greatest—and most obvious—ecosystem service that dung beetles provide, according to Dr. Bryony Sands, an entomologist at the University of Vermont. Without dung beetles, manure can sit on the surface for up to a year, and cows won’t graze near the stagnant stool, she said. But the benefits far exceed creating clean and nutritious soil.
“These organisms, down to the insects that live in poop, are so vital and need to be looked after.”
“The other things that live in manure are pests and parasites,” she added, which would otherwise infect the gut of the cattle. These pests can nest in stagnant stool, but dung beetles break those down, dry them out, and physically remove them from the surface of the pasture. Popular pesticides like Ivermectin can control pests, but they poison dung beetles. For farmers like Hansen who use a more natural approach, the dung beetles can help eliminate the need for pharmaceuticals in the first place.
Dung beetles have even been shown to reduce greenhouse gas emissions from cattle farming, especially from methane, shortening the amount of time that the fuming stool sits on the surface. One 2016 study suggests that they reduce emissions on pastures by 12%. “That’s one of the most amazing things that we’ve discovered very recently,” said Dr. Jorge Ari Noriega, an ecologist at Universidad El Bosque in Colombia.
Those services aren’t limited to farms, Noriega said. They apply to forests, savannahs, grasslands, and other biomes, too. In fact, natural ecosystems might even have added benefits—ones that have earned dung beetles the title of ecosystem engineer.
In forests, for example, dung beetles break down droppings from primates and other fruit-eating mammals. The stool contains seeds, which the dung beetles disperse as they roll them away and bury them. Some plants even produce seeds that resemble dung balls, deceiving beetles into dispersing and burying them.
“They are affecting, in some ways, the structure of the forest,” said Noriega. Given their small size, their individual actions are easy to overlook. “But one billion individuals are doing the same thing—that has a huge effect… a huge, huge, positive effect.”
Good Omens
The state of Hansen’s dung beetles reflects the farm as a whole. “One thing out of balance will put other things out of balance, so if we’ve got a good dung beetle population, then theoretically, other things should be in balance, too,” he said.
Noriega has shown that dung beetles are bioindicators of habitat perturbation in the wild as well. “Dung beetles have a really strong connection with the environment, especially with vertebrates and the forest structure. If these things change, the group changes in species richness, in abundance, in biomass,” he said.
If forests burn, for example, then herbivore populations falter, and dung beetle populations collapse. Forest recovery, which depends on seed dispersal, slows down without the industrious insects around. If pesticide use proliferates, then beetle populations decline, allowing more pests and parasites to dwell in the stagnant dung. Even when land is allotted to ecotourism—and nominally, conservation—human presence displaces mammals, which in turn, drives down dung beetle numbers, Noriega has discovered.
Both on farms and in the wild, dung beetles portend good fortune when they’re abundant and collapse when they disappear.
In various regions around the world, studies have suggested that dung beetle populations have waned in recent decades due to land use change, pesticide use, and hunting of large mammals. Noriega added that climate change poses an additional threat.
“[Scientists] are a little worried that some species could disappear,” he said, although in many places in the tropics and the global south, there’s simply not enough research to know how dung beetle populations are faring.
Given their role as bioindicators and ecosystem engineers, experts are waiting with bated breath to see how dung beetles will navigate the insect apocalypse, a concerning loss of insect biomass in recent decades. “These organisms, down to the insects that live in poop, are so vital and need to be looked after,” Sands said.
In dire times, like our present planetary crisis, cliché wisdom suggests that we look to the skies for guidance. But maybe, we should leave the stargazing to the beetles and, instead, look for clues in the overlooked, cast-aside corners of the world—maybe we should look in the dung.
