How to Identify Dung Beetles: Horns, Color, Size
How to identify dung beetles comes down to three checks: body shape, antennae shape, and whether you catch one rolling or burying. The family Scarabaeidae holds over 35,000 beetle species worldwide, and the true dung feeders in the subfamily Scarabaeinae make up a few thousand of those, so a handful of physical checks narrows things down fast.
What Makes a Scarab a Dung Beetle
Dung beetles feed and breed on the feces of other animals, mostly herbivores and omnivores. That single habit shapes almost everything about their build: a compact, armored body for pushing through dung and soil, and forelegs adapted for digging or rolling rather than climbing.
Three nesting styles cover nearly every species. Rollers shape a ball and roll it away from the dung pat before burying it. Tunnelers dig straight down and pack chambers with dung under the pile itself. Dwellers skip excavation and just breed inside the pat. Watching which one a beetle does on-site is often a faster ID clue than any single field mark.
Size and Body Shape
Most dung beetles run from about 5 mm to 30 mm long, though a few species reach 50 mm. Body shape splits roughly into two camps: rollers tend toward a rounded, almost spherical build that’s easier to push a ball with, while tunnelers and dwellers run more oval or elongated. A quick length check against a coin or ruler, paired with the overall outline, rules out a lot of look-alikes immediately.
Color and Elytra
Coloration ranges from flat black or reddish brown to strongly iridescent metallic green, blue, or copper, and the sheen can shift with the angle of light. The elytra, the hardened forewings, are worth a close look too: some species show fine ridges called striae or rows of small pits called punctation, while others are nearly smooth. A beetle that looks plain black in shade can flash green or copper in direct sun, so check color in good light before ruling a species out.
Antennae and Horns
Dung beetle antennae end in a clubbed, lamellate tip made of flattened plates that fan open to sense odor and close back up at rest. That clubbed shape alone separates them from most other beetle families.
Horns are a male-only feature in many genera, and their size is driven by larval nutrition as much as by species. In Onthophagus taurus, well-fed larvae grow into “major” males with long, curved horns sweeping back from the head, while poorly-fed larvae become small, effectively hornless “minor” males, and females lack horns entirely. So a hornless beetle is not automatically a different species, and horn size alone is an unreliable way to separate species without also checking body size and color.
Where to Look
Habitat narrows the list further. Rollers favor open ground such as pastures and grasslands, where there’s room to push a ball in a straight line. Tunnelers and dwellers turn up under dung piles in forests, deserts, and grazed fields alike. Checking what animal left the dung matters too, since many species specialize on cattle, horse, or wild herbivore droppings rather than feeding on whatever they find.
Using Photos and Field Guides
Photograph specimens from the top, the side, and the underside if you can safely flip one, since horn shape, leg structure, and elytra texture each show up best from a different angle. A regional field guide narrows the species list to what’s actually plausible in your area, which matters since many genera look similar at a glance. Where local rules allow collecting, a preserved specimen under magnification makes small features like punctation and antennal segments far easier to check than a live, moving beetle.
Four Species to Know
Bull-Headed Dung Beetle (Onthophagus taurus)
Small at 8-10 mm, black or reddish brown, sometimes with a faint metallic sheen on the pronotum. Major males carry sweeping curved horns; minor males and all females are hornless.
Green Dung Beetle (Canthon viridis)
A green tumblebug in the roller genus Canthon, roughly 10-20 mm with a metallic green sheen. Most often found in open fields where large herbivores graze.
Sacred Scarab (Scarabaeus sacer)
One of the larger species at roughly 19-40 mm, with a rounded body and shiny black elytra that can show faint striations. A classic roller, historically linked to ancient Egyptian iconography.
Rainbow Scarab (Phanaeus vindex)
Missouri’s field guide lists the rainbow scarab at half an inch to three-quarters of an inch long, with a bright metallic green and copper body, orange antennae, and a backward-pointing horn on males. Females lack the horn but keep the same metallic coloring, and both sexes have a single spur above the “foot” of each hind leg.
Telling Similar Species Apart
When two candidates still look close, check horn presence and shape first, keeping in mind it can vary within one species, then color and sheen under consistent light, then exact size range, then habitat and host dung. Stacking three or four of these checks together, rather than relying on any single trait, is what actually separates similar-looking dung beetle species in the field.
