Edmonton, Canada — For most people, the prospect of collecting and sorting through piles of bug excrement is an experience best left to contestants on Fear Factor.
Tyler Cobb chose to do it for his PhD thesis.
Specifically, the University of Alberta graduate immersed himself in the droppings of the white-spotted sawyer, a species of long-horned beetle that feasts on dead or dying trees scorched in a forest fire.
Years invested as a beetle pooper-scooper eventually paid off, as Cobb’s analysis found the fecal matter plays a vital role in helping burned forests to regenerate.
“At some point in my studies, I started think about the ecological role the beetles play, and that’s what led me to dung,” Cobb said. “Most people understand how fertilization works because they are used to fertilizing their lawns. It’s not a big jump to realize that forests need nutrients as well, and essentially the beetles are providing that for free.”
In conducting his research, Cobb chose to study an area of northern Alberta forest that was burned in the massive Chisholm wildfire of 2001.
As with other burned forests, the trees charred in the Chisholm blaze were quickly set upon by pyrophilous or “fire-loving” beetles. The insects, which are attracted by the fire’s heat or smoke, attack burned trees because their natural defences have been weakened or destroyed, Cobb said.
The adult beetles lay their eggs in the soft inner bark, where the larvae feed continuously during the two years it takes for them to mature.
“It’s something you can actually hear happening as you walk through a burned forest,” Cobb said. “There is this kind of sound like a rocking chair … and that’s the sound of the larvae feeding under the bark.”
As the beetles eat, they push out their fecal matter. This material, known as frass, rains down out of the tree and builds up around the base in piles that resemble cones of sawdust, he said. The frass then gets into the soil, where microbes are stimulated to transform the material into nutrients that other plants can use.
“It’s a nutrient-cycle pathway,” Cobb said. “Essentially, the beetles are breaking the tree down into smaller bits so microbes can start to work on them.”
Collecting enough dung for his experiments — about 10 grams — took Cobb nearly a year. Since the samples had to be uncontaminated, he was forced to rear his own beetles in the lab by feeding them burned timber.
After picking up those beetles’ frass, it then took another year to properly prepare the material for chemical analysis.
“It’s two parts essentially, wood shavings mixed in with the fecal pellets,” Cobb said. “So a lot of time is spent under the microscope with a pair of tweezers sorting out beetle poop from the wood shavings — as glamourous as that sounds.”
Now that he knows what role beetles play in forest regeneration, Cobb is concerned about the effects of post-fire salvage logging. When companies harvest wood from a fire-ravaged area, they also take away the beetles’ larvae before they have had a chance to perform their ecological job. Over time, this makes it more difficult for new plant life to spring up.
“What we’re finding with several species of these pyrophilous beetles is that their numbers have dropped dramatically in salvage-logged areas,” Cobb says. “When you remove the beetle, you remove the beetle dung, and you remove this nutrient-cycle pathway that helps to replenish the soil with nutrients.”
Cobb suggested logging companies should delay their salvage operations for a couple of years after a fire to allow a generation of larvae to develop. Or, they could leave some burned wood in place.
Now the curator of invertebrate biology at the Royal Alberta Museum, Cobb said one of his major goals is to help people learn to better appreciate bugs.
“I think every kid goes through a bug phase in their childhood, and I guess I never outgrew mine,” he said.