Dung beetles have a dirty but important job
South Dakota is home to some 3.6 million-head of cattle. Many of which spend their days grazing on acres and acres of grassland. And like all creatures, what goes in, must eventually come out.
So, what happens to all those cow patties? Patrick Wagner has at least one answer. Dung beetles.
“Yeah, it’s gross, they feed on dung. But you know, it’s a dirty job, but somebody’s gotta do it. And in the process of feeding on the dung they’re doing so much for the environment, for pest control, they just do so much for the ecosystem,” Wagner said.
Wagner knows a lot about dung beetles because they were the focus of his graduate research. Today he is an SDSU Extension Entomology Field Specialist.
And because he’s spent countless hours inspecting dung beetles under a microscope, Wagner is the perfect person to describe what a dung beetle looks like.
“Basically they are going to look like a small, black, usually shiny beetle. Depending on the species, they can be anywhere from less than a half inch to maybe an inch or more long. They’re all going to have that hard shell that’s characteristic of beetles and they are going to be found around dung,” Wagner said.
Using scent as their guide, once a patty is dropped, dung beetles fly in and get to work, taking dung from the surface and moving it into the soil profile where instead of releasing CO2 into the atmosphere, the dung provides nutrients to plants as it decomposes.
Wagner explains that depending on the species of dung beetle there are a few ways they do this.
Dweller dung beetles break down the cow patty as they burrow inside making homes throughout the pile for the eggs they lay.
Then there’s the tunneler dung beetle. Patrick Wagner explains how they do their job.
“They will get to the dung pile and make these tunnels or chambers in the soil, underneath the dung. In those chambers, we call them brood chambers, they make dung balls, pack them into the chambers, lay eggs on them and that is one of the ways the dung beetles integrate the dung into the soil,” Wagner said.
The dung beetle we can all see working is the roller dung beetle. Again, Patrick Wagner.
“Those are the largest of the dung beetles. So, they will show up, carve out a little piece of dung from the outside and they will roll it into a ball and roll it away from the dung pile. Find a place, dig a hole, bury it and then they will protect that dung ball that will contain eggs for the next generation,” Wagner said.
Depending on the size of the dung beetle population in a pasture, Wagner says a cow patty can disappear from the landscape in a week, a day or even within the hour.
This is the experience on a Philip ranch owned by MaryLou and Pat Guptill.
“I’ve taken pictures of a patty that was on the ground for less than 30 minutes, had 43 dung rollers on it in 30 minutes and in 15 minutes after that it was gone. So, those dung beetles are putting that nitrogen back into the soil,” Guptill said.
Free fertilizer to bolster their grassland health is key to Guptill’s intensive, year-round grazing plan. Unlike many South Dakota ranchers, Guptill and his wife, MaryLou graze their cow-calf herd out on their grassland year-round.
Dung beetle populations have not always been high on the Guptill Ranch. The couple began to see a visible increase about three years after they quit applying chemical, pour-on insecticide to their cows.
Entomologist Patrick Wagner explains the connection.
“It really comes down to whatever pesticide products will have a residual in the dung. Some of those products are designed so that way when the flies eat it, they will die. In the process, that is the only food source for your dung beetles – so, you have those non-target impacts killing your dung beetle populations off as well,” Wagner said.
Because most flies and their offspring depend on dung piles for food, when dung beetle populations are up and cow patties are not available on the soil surface, fly populations are greatly reduced.
Pat Guptill says that because of increased dung beetle populations on their ranch they have gone for more than 20 years without needing to use chemical fly control.