Been there, dung that

What if ranchers could find a way to increase grazing, recycle nitrogen, reduce the number of pest flies, increase forage yield, improve soil water retention and ground aeration, lower animal disease rates and beautify landscapes?

What would such combined services be worth?

Regardless of the number, the dung beetle does it all and does it for free.

There are 300 species of dung breeding insects in Canada, and dung beetles are among them, said entomologist Kevin Floate of Agriculture Canada in Lethbridge.

It’s a case of been there, dung that for the beetles.

They break down cow patties so grass can grow again, return nutrients to soil and reduce habitat for flies bothersome to cattle.

Floate said dung beetles can make short work of manure, depending on the type of beetle and environmental conditions.

“I have seen them rip apart horse dung in a matter of a few days,” he said.

“When you get literally 2,000 or 3,000 beetles, even though they’re pretty small, just that activity … it essentially eliminates (manure) as a negative force in the pasture within a week.”

Adult dung beetles feed on bacteria in manure. Sieve-like mouthparts allow them to squeeze the material and extract micronutrients. Thus fortified, the beetles lay eggs and the larva feed on plant fibre within the manure.

Similar to a cow’s rumen, dung beetle larva have expanded guts that produce enzymes for digesting fibre.

“A dung beetle larva may eat their own weight every day in plant fibre just to get enough nutrients to develop,” said Floate.

Most dung beetles overwinter as adults, reappear and lay their eggs in spring. Larva feed on manure through mid-summer before emerging as adults in fall.

There are some native species of dung beetle, but most species in Canada came from Europe during settlement and subsequent cattle import and movement.

They arrived ready to start work.

“All the European species that we see in cattle dung are sort of generalists with dung of a big round pie: bison dung, cattle dung,” he said.

“We do have specialists in the sense that some dung beetles have a strong preference for maybe horse dung, but you also find them in cattle dung, or vice versa.”

Floate and his colleagues have surveyed dung beetles and researched the results of their activity. Cow pies in pastures without dung beetles become virtual hockey pucks that can potentially remain intact for years.

“But if you have insect activity, the insects themselves are tunneling, they’re feeding, they’re breaking up the manure,” he said.

“And by breaking up the crust, they’re allowing water to get in, they’re allowing plants better access from beneath.”

Insect presence attracts birds, which play their own role in manure redistribution.

Floate said he occasionally gets concerned inquiries about manure that fails to break down. His first question is, “when was the manure deposited?”

Insects can’t colonize manure in winter, so those cow pies will likely be around longer than those dropped in spring.

“Where insect activity is most important is probably shortly after turnout, so May, June, maybe early July,” he said.

“That’s when the dung beetles are actively laying eggs, tunneling, feeding, and dung beetle larva are developing and feeding.”

Beetle activity lulls in the peak of summer, but many other beneficial flies, fly parasites, beetles and mites also enjoy a good pie.

Who doesn’t?

Floate tells of mites that ride on flies and dung beetles “like passengers on a bus. The dung beetle is the bus. When it arrives at a fresh cow pie, the tiny little mites hop off.”

However, that’s not the end of the trip. The mites feed until new dung beetles develop from larva.

“The mites will line up and wait for the new dung beetle adult to leave, sort of like passengers waiting at a bus stop… It’s pretty amazing, actually.”

The caveat on this insect activity comes in the form of cattle insecticides. Products applied to cattle to control parasites and pest flies can be passed in manure and limit subsequent insect activity.

The scope of those effects depends on the product and when it was applied.

Insecticides can do the job if the goal is to kill pest flies, but the choices are different if the focus is on preserving dung beetles and other beneficial insects.

“In our studies, we have shown several times that if you apply the recommended dose of a certain product to cows in the spring, there’s enough residue in the fall, in fresh manure being deposited by that animal, to suppress at least the development of some insects,” Floate said.

“Whether that’s good, whether that’s bad, it’s a judgment call.”

Ivermectin, the most studied cattle-applied insecticide, is commonly used in fall.

The absence of insects in winter reduces the impact, and manure residue is gone by the time cattle are turned out in spring.

Treatment in spring is a different story, and probably the worst case scenario for dung beetles, Floate said. Research has found reduced insect activity in manure for up to 12 weeks after insecticide application.

Dung beetles find manure by following an odour plume, which they detect through sensors in their antennae. They are efficient flyers and will travel for more than a kilometre if the potential meal smells good.

There are three types: dwellers, tunnellers and rollers.

Most species in Alberta are dwellers. They are attracted to fresh cow pies, where they eat bacteria and lay their eggs.

As the name implies, tunnellers will bury bits of manure five to 20 centimetres below the surface, where the material will feed the larva.

Rollers take a piece of manure and push it away from competitors. Then they bury it in a small ball, inside which they’ve laid an egg. When the larva emerge, their meal is ready.

Floate said dung beetles are not pests “in any serious sense,” although some farmers suspect that the larva from one dung beetle species feeds on crops where manure has been spread.

He is not yet convinced they cause damage worthy of any control efforts because damage is usually spotty.

Floate has researched a number of different insects, ranging from wheat blossom midge to livestock pest flies.

And dung beetles, of course.

The work continues to fascinate and he likes to share his interest, though he has a squirm-inducing way of putting it.

“One of the greatest pleasures I get is getting out of my office, away from my desk, sticking my hand in cow dung and sharing this passion with other people.”

Click here to download “Common dung beetles on pasture” in PDF format.


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