I shared an essential piece of culture with my fiancé this week: the 1999 movie The Mummy.
It’s a great movie (okay, maybe not “great,” but definitely a fun romp). I have a complaint, though. In the film, scarab beetles are shown as voracious flesh-eating carnivores. This is a blatant lie! Scarab beetles don’t eat flesh – they eat dung.
That’s right: scarab beetles are just a specific species of dung beetles.
There are about 8,000 different species of dung beetles, all part of the insect family Scarabaeidae. Depending on the species, they are between 0.5 and 2.5 inches long (1.3 to 6.3 centimeters). You can find dung beetles on every continent in the world except Antarctica.
As you might expect from the name, most dung beetles eat feces. They usually graze from the poop of herbivores, whose feces often contain half-digested grass and a smelly liquid. The liquid is the food for dung beetles, as it’s full of microorganisms they can digest. But not all dung beetles are dung eaters! Some have a more “normal” diet of mushrooms, carrion, and decaying leaves. One Peruvian species even hunts millipedes!
Three types
There are three different types of dung beetles: dwellers, tunnelers, and rollers. Each type interacts with dung differently.
Dwellers live on the tops of dung pats. They lay their eggs on the surface of manure, and the young develop within the dung. Dwellers tend to be smaller than tunnelers in rollers.
In contrast to dwellers, tunnelers bury themselves in dung pats. After finding a pile of poop, a tunneler will tunnel straight down and dig a hole underneath. This hole serves as both a home and a place to store dung – just like we refrigerate food, keeping dung underground preserves freshness and helps keep predators and parasites away. The male tunneler is in charge of bringing home more poop, while the female arranges it throughout their tunnel home. Depending on the species, one or both parents will stay with the larvae as they develop.
You probably think of rollers when you think of dung beetles. These insects create giant dung balls that serve as food for an adult pair or as a place for the female to lay her eggs. After meeting at a dung pat, a male roller will offer his dung ball to a female. If she likes it, they roll away together to find a nice place to bury it. This buried dung ball is where the pair’s larvae will grow into adults. Only about 600 of the 8,000 species of dung beetles are rollers.
Egyptian superstars
The ancient Egyptians found these rolling dung beetles significant. More specifically, they venerated the sacred scarab (Scarabaeus sacer). The sacred scarab was thought to be a symbol of the god Khepri. Khepri’s main job was to roll the sun across the sky like the sacred scarab rolled dung across the ground. The scarab also became an image of rebirth and renewal, making it a popular image in ancient Egyptian religious and funerary art.
Here’s another fun fact: the Ancient Egyptians thought all scarabs were male. After seeing larvae emerge from dung balls, they came to the (incorrect) conclusion that scarab beetles reproduced by injecting their sperm into dung. The female actually lays a single egg in a dung ball she buries in the ground.
Rolling along
The most impressive thing about rolling dung beetles is how quickly and straight they roll. Dung beetles will fight over dung balls, so they want to roll up some poop and scurry away as fast as possible. They also want to move in a straight line to avoid ending up in the dung pile again (and next to potential rivals).
But moving in a straight line is surprisingly tricky. Most animals will quickly start drifting and spiraling when walking without a reference point. Dung beetles have it extra hard: they roll their balls with their back legs while their heads are pointed toward the ground.
Still, dung beetles have impressive navigational skills. They can use the sun as a reference point to determine direction. When the sun is at its zenith, they can switch to using wind for directionality. What about when it’s nighttime? Easy! Dung beetles can orient by the moon. And if the moon isn’t around, they switch to navigating by the Milky Way. This makes dung beetles the first known animals to use the Milky Way to travel (their eyes aren’t good enough to see individual stars, which other animals use to travel at night).
Still not convinced dung beetles are really that great? How about this: without dung beetles, we would have a lot more flys buzzing around. A cow produces 10 to 12 dung pats daily, and a single pat can produce 3,000 flies in just two weeks. Dung beetles help keep this poop from hardening on the ground and killing plants, and they keep the fly population under control. In Texas, for instance, dung beetles bury about 80% of the poop produced by cattle. Imagine how many flies we’d have without dung beetles!
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