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Dung Beetles – What Are They All About?
DR. DIRK PHILIPP
FAYETTEVILLE, ARK.
Dung beetles certainly don’t invoke an immediate sense of appreciation, given the preferred habitat of this industrious insect of the order Coleoptera. However, there is some solid scientific evidence behind the benefits of having dung beetles on your pastures.
The main activity of dung beetles is to take on the fecal patties cattle leave behind. These patches decompose over time, releasing nutrients into the soil but also emitting ammonia, thereby reducing the amount of N added back to the pastures. Dung beetles are able to help decompose those patches much more quickly and distribute fecal material much more evenly.
The amount of feces put onto a pasture can indeed be large: during one day, a cow typically covers around 10 square feet with dung and urine. A pasture can be covered anywhere from 10 to 35 percent with patches, depending on stocking rate. Because the recycled nutrients are now concentrated on a small area, the forage below the patches doesn’t take well the nutrient overload. Studies have shown that after 15 days, roughly 75 percent of plant tissue decomposed underneath the patches. The patches also affect grazing behavior. Cattle do not graze around the patches for some time, possibly due to smell and palatability. Although they return to graze around the fecal areas at a later time, forage growth there will not be as efficiently utilized as in between the patches. So, the challenge is how to get the cow patties incorporated into the soil as quickly as possible.
That’s where the dung beetles come into play. Their main benefit is burying the dung into the ground, usually between 4 to 12 inches deep, and making the nutrients available to plant roots. As beneficial side effects, the burying and translocating of feces result in aeration of the soil and an increased water infiltration rate that helps keep rainwater on site and may reduce runoff from pastures. It has been estimated if patties remain unburied, N losses are substantial. Only 15 percent of the excreted N is then made available to plants in the mid-term, because the N will get lost through various pathways, including volatilization.
When it comes to phosphorus, the main mechanism of returning it to the soil is the physical breakdown of patches and less the leaching. Some researchers even suggested that when grazing pressure is high on patty-covered pastures, mineral imbalances could result from forced grazing of forage growth around these patties. The fly populations have also been shown to decline with increasing numbers of dung beetles. Horn flies and face flies lay their eggs in the patties, and the dung beetles compete with the larvae for food and sometimes physically damage them.
Keeping dung beetle populations high or even increasing them in a pasture ecosystem is not easy as they are sensitive to insecticides used to treat internal parasites and flies. If feasible, pesticides formulated in an ear tag are preferred and have minimal impact on dung beetles. Backrubber insecticides and sprays do not have large negative effects either on dung beetle populations. Animals can also be treated during the colder months of the year when beetle populations are low. If in doubt, producers can submit fecal samples to a veterinarian to determine if the observed symptoms are due to internal parasites.
Grazing management also affects dung beetles. If grazing is controlled over smaller areas, the number of patties will increase and should have a positive effect on the beetles by providing a food source without the need to roam further. To determine whether dung beetles make your pasture their home, check on the cow patties. Beetles move in literally within minutes during warm days once a fecal pat has been dropped. Look out for holes in the surface or open the patties with a spade to confirm the presence of these helpful insects. ∆
DR. DIRK PHILIPP: Associate Professor/Forages, University of Kentucky
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