Nachusa's Underappreciated Clean–up Crew

By Dr. Nick Barber

Bison Bull

​The bison reintroduction has been exciting for everyone involved with Nachusa—staff and stewards, volunteers and visitors, and especially scientists. The project provides a unique opportunity to measure the impacts of these animals and their actions on the entire restored prairie ecosystem. I’m fortunate to be part of a small army of researchers and students working closely with Nachusa personnel to understand how bison influence plants, animals, and other organisms. 

Nick Barber gathers fresh dung to bait the beetle traps

​Anyone who has had the opportunity to spend time within the bison units over the past 2 years has undoubtedly seen evidence of these giant herbivores: dung! In addition to grazing on plants and wallowing in dirt, bison play an important role in nutrient cycling by depositing concentrated piles of plant material and nutrients around the prairie. Across the landscape, this may provide hotspots of growth for some plants, adding to the overall diversity at Nachusa. 

Opaque earth boring beetles (Geotrupes opacus) are the largest dung beetles documented so far at Nachusa.

​An inconspicuous group of insects help to carry out this nutrient–cycling process. Dung beetles feed on animal waste, and many species collect dung as a food source for their offspring. Some species famously form it into spheres, and roll these “dung balls” away to bury and deposit eggs. Other species tunnel below the dung patty, building chambers where dung is stored and beetle larvae can develop. And some species are “dwellers” who simply dive in to fresh dung and start to feast, laying eggs along the way. When these eggs hatch, the larvae feed, pupae, and emerge as adults, completing their entire metamorphosis in a single patty before heading off to mate and start the process over again in fresh patty.
 
Burying small bits of dung in the soil helps make nutrients accessible to plant roots. In the soil, microorganisms like bacteria and fungi convert organic materials into inorganic forms available to plants. This can represent a significant amount of the nutrients. As dung dries, much of the nitrogen can be lost to the air as ammonia volatilizes. This is why dung beetles are important for ranching:  every bit of nutrients back in the soil rather than lost to the atmosphere means more fodder for livestock.

A dung–baited pitfall trap

​So it was a reasonable assumption that the dung beetle community at Nachusa would respond positively to the introduction of several dozen large, dung-producing herbivores to the prairie. I credit Dr. Ken McCravy from WIU for first suggesting that we should investigate these communities. Over the past two years, with support from the Friends of Nachusa Grasslands, I have been working with NIU students to survey the dung beetles to determine which species are present and how their abundances differ between sites with and without bison. We use pitfall traps, baited with fresh bison dung, to collect beetles that are later pinned and identified under a microscope in my lab at NIU.

Rainbow scarab (Phanaeus vindex) is an uncommon but beautiful species.

Our preliminary results are exciting:  we have documented at least seven species, including rollers, tunnelers, and dwellers. The two most common species are Onthophagus hecate, a widespread species, and Onthophagus knausi, a uncommon species whose range extends west and south through Kansas, Oklahoma, and Texas. The other species are much less common but include the large, blue-black Geotrupes opacus and the spectacular rainbow scarab, Phanaeus vindex. ​

Back at the lab, Nick separates the insects captured in the pit–fall trap.

Identifying the beetles often requires careful inspection of microscopic traits.

 As a preliminary result, the presence of bison doesn’t seem to have a big effect on abundance, as some bison-free sites have high numbers of beetles. But this may not be surprising given how mobile these insects are. They can fly and specialize in seeking out their preferred food. Cattle pastures surrounding Nachusa likely provide population sources as well. 
 
Over the next two years, we will be investigating these dung beetle communities in more detail. A Master’s student at NIU will be combining observations of dung decomposition with beetle measurements to understand how different species contribute to dung processing. Ultimately we hope to understand how the management actions that maintain high plant diversity at Nachusa (such as prescribed fire and grazing) affect beetle communities and their ability to process dung. 
 
Keep an eye on fresh dung patties and you may see these small but fascinating insects carrying out some of the invaluable “dirty work” that keeps the prairie ecosystem healthy and biodiverse!

Asters and goldenrod are in full bloom last fall as Nick sets his traps.

Nick Barber is an assistant professor in the Department of Biological Sciences at Northern Illinois University. To read more about his work, visit the Barber Lab webpage. Thank you Nick, for being our guest blogger this week!