Enlisting Insects for Soil Health

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A bumblebee enters its nest. Most native bees nest in the ground and need access to the soil.

By Chase O’Neil, Farm Planner

I’ve always struggled to love insects. And I’ll admit, I am judging a book by its cover: their shiny carapaces, their eerie antennae, and their chaotic movements all give me a case of the heebie jeebies.

Yet, after reading Farming with Soil Life: A Handbook for Supporting Soil Invertebrates and Soil Health on Farms, I’m finding a new appreciation for these creepy crawlies (and other soil life too!) While microbes usually get most of the attention, soil fauna (or animals) are vital for breaking down organic matter like manure and making the nutrients more accessible to plants. Soil fauna also improve soil structure by mixing nutrients into the soil and by facilitating the movement of air, water, and roots through the soil.

One insect that perhaps deserves more of our attention is the dung beetle. While I always pictured dung beetles rolling around manure balls in African grasslands, they exist in Washington state too, and they aren’t always rollers.

In fact, did you know that…

  • Dung beetles are classified into three groups based on their “food relocation behavior”:

    • Paracoprids: “tunnelers” who nest underneath the manure, drawing manure below the soil surface.

    • Telecoprids: “rollers” or “tumblers” who move part of the manure away from the original location and bury it.

    • Endocoprids: “dwellers” who nest inside the manure. 

  • Sometimes dung beetles steal manure balls from others!

  • By burying and feeding on dung, these beetles help soil health by breaking manure down quickly, cycling nutrients, mixing up soil particles, and improving water infiltration rates. Ultimately, dung beetle activity may benefit downstream water quality.

  • Dung beetles have also been found to decrease manure pathogen and pest populations:

    • For example, on grazed pastures, dung beetles can reduce pathogenic nematodes and flies.

    • Another study found dung beetles help rapidly process manure on vegetable farms and can reduce pathogenic E.coli from swine manure (a few sites included in the study were in Washington state!)

Onthophagus nuchicornis, a species of dung beetle. Photo Credit: Wikimedia Commons AfroBrazilian.

Unfortunately, like many other soil invertebrates, dung beetles are heavily impacted by pesticides, particularly those used to treat livestock for parasites (parasiticides). A research study on organically-managed farms found a higher diversity of dung beetles and faster manure breakdown when compared to conventional farms.

For tips on how to continue treating cattle for parasites while also protecting dung beetle populations, see Washington State University’s helpful extension article. On the plus side, managed grazing, such as rotational systems, can increase dung beetle populations and diversity by influencing manure concentration and distribution and improving pasture forage health. 

To learn more about the many interesting organisms that provide soil health benefits (although, be forewarned, not all of them are as “charismatic” as the dung beetle) and how to avoid practices that negatively affect them, check out the Xerces publication “Farming with Soil Life: A Handbook for Supporting Soil Invertebrates on Farms.” On pages 117-123 you’ll find a list of practices from the Natural Resources Conservation Service (NRCS) that support soil organisms. 

This project (WQC-2022-SnohCD-00101 Nutrient Runoff Reduction From Agricultural Lands in Snohomish County) was made possible through a Centennial Clean Water Fund grant through the Department of Ecology.