What Do Dung Beetles Eat? Rollers, Tunnelers, and Dwellers
What do dung beetles eat? Mostly feces from herbivores and omnivores, along with the fungi and microbes living inside it. Dung beetles don’t digest whole feces so much as filter it: they extract the liquid fraction, fine plant fibers, and microbial protein, while larvae in the brood ball rely more heavily on bacteria and fungi to pre-digest the tougher material.
What’s Actually Inside a Dung Pile
Fresh dung is mostly undigested plant fiber, water, and a dense population of bacteria, protozoa, and fungal spores that came through the host animal’s gut. For an adult beetle, the microbial fraction and the liquid portion are the real prize, since they contain more usable protein and nitrogen than the fiber itself. Cattle and horse dung, both from large grazing herbivores, tend to attract the widest range of species because the pats are large and moisture-rich for days after they’re dropped.
Nitrogen, Phosphorus, and Carbon
The nutrients that matter most to a feeding beetle are nitrogen (from proteins and microbial cells), phosphorus, and carbon compounds from plant fiber. If manure is left exposed on the soil surface, a large share of its nitrogen volatilizes off as gas rather than staying available to plants; West Virginia University Extension notes that manure left on the surface loses much of that nitrogen to microbes that release it as gas instead of it remaining in the soil. Beetles that bury dung intercept some of that nitrogen before it’s lost.
Rollers, Tunnelers, and Dwellers
Entomologists split dung beetles into three feeding and nesting guilds based on what they do with a dung pat, not what they eat within it. All three guilds eat the same basic resource; the difference is where they process it.
Rollers (Telecoprids)
Rollers cut a piece off a fresh pat, shape it into a ball, and roll it away from the pile before burying it. A male will often shape a brood ball and roll it together with a female to a burial site, where she lays a single egg inside; the emerging larva then eats that ball from the inside out. Moving the food away from the pat cuts down on competition from other beetles at the source.
Tunnelers (Paracoprids)
Tunnelers skip the rolling step and dig straight down beneath the pat, packing dung into side chambers as they go. Because they work in place, they can exploit both the fresh surface layer and the older, partly decomposed dung underneath. Their tunneling loosens and aerates the soil directly under the pile, which speeds up how fast the rest of the pat breaks down.
Dwellers (Endocoprids)
Dwellers never leave the pat. They live and feed inside it or near its base, laying eggs directly in the dung mass instead of building a separate brood chamber. Because they stay put, dweller species are usually the first to colonize a fresh pat and can reach very high densities in pastures with steady livestock traffic.
Fresh Dung vs. Aged Dung
Not every species wants the same pat. Many rollers and some tunnelers key in on dung that’s only hours old, when moisture and microbial activity are highest. Dweller species and some tunnelers are more tolerant of older, drier dung, since they can still extract nutrients from the fiber and microbial residue left behind after the fresh material is used up. This is why a single cow pat can host several different species at once, each working a different layer or age of the same resource.
Why Rainfall Changes the Menu
Dung beetle activity tracks livestock and wildlife density, and both shift with rainfall. After rain, grazing animals are more active and produce more frequent, moister droppings, so fresh dung is easier to find and beetles concentrate their feeding on it. In dry stretches, fresh pats dry out and harden within hours, pushing beetles toward whatever older, still-workable dung remains, or toward pats deposited in shaded, damp microsites.
Gut Microbes Do Part of the Digesting
Dung beetles can’t break down fiber on their own. Bacteria and fungi already present in the dung, and additional microbes carried in the beetle’s own gut, ferment plant fiber into simpler compounds the beetle can absorb. Larvae depend on this even more than adults do: the brood ball is inoculated with microbes from the mother, and that microbial community continues breaking down the ball’s contents while the larva develops inside it.
What Beetles Give Back to the Pasture
Feeding is also how dung beetles do their ecological work. Burying and tunneling moves nutrients from the surface into the root zone, and South Dakota State University Extension points out that breaking down dung piles assists with suppression of dung-breeding livestock pests, including flies, parasitic nematodes, and protozoa that would otherwise complete their life cycle in an intact pat. The effect on parasites can be substantial: West Virginia University Extension reports that aggressive dung beetle activity in a pat reduces helminth egg counts four- to fifty-fold. A pasture with an active, diverse dung beetle community typically clears dung pats within days instead of the weeks it can take without them.
