Dung Beetles: An Overview

Insects (beetles, bees, ants, ladybugs, and many more) live all around us and are responsible for carrying out many important tasks in most ecosystems on Earth, even in cities where many people live. These helpful tasks, called ecosystem services, ultimately benefit humans. Some of the critical ecosystem services performed by insects include pollinating flowers, recycling dead organisms (leaves or animals, for example), and protecting crops from pests that would eat them. But have you ever wondered exactly what insects are? Insects are a group of invertebrate animals (that is, animals without backbones) that come in a wide variety of species. All insects have one pair of antennae, three pairs of legs, and two pairs of wings.

Dung beetles are insects commonly known for using manure (animal poop) to survive (Figure 1). Much research on dung beetles has been done in tropical forests (for more info, please see this Frontiers for Young Minds article). Dung beetles also exist in semiarid environments, where climate is extreme with very little rain and high temperatures. In Mexico, these environments are found in the center and north of the country. It is common to think that few species could exist in these hot, dry environments, but semiarid environments actually contain a great variety of life forms. Little is known about the function of dung beetles in semiarid environments. Do you think the dung beetles might do the same job there as they do in tropical forests, where they remove dung and contribute to nutrient cycling and soil enrichment, plus they have been found to contribute as much to seed germination?

Dung Beetles: Small Insects Doing a Big Job

We studied the dung beetles that are distributed throughout pastures located in the semiarid areas of the Potosino Highlands, which are part of the southern Chihuahuan Desert. We found a great variety of dung beetles in this ecosystem [1]. The most abundant is a species called Canthon humectus, which is a roller dung beetle (Figure 2). Usually, dung beetles work in pairs (one male and one female). The male is the first to arrive at the dung, and he forms it into a ball. Then the female arrives, and together they roll the dung ball until it is buried in the ground. Once the dung is buried, the dung beetles use it as a nest—a place to lay their little eggs and to feed.

We were curious about the importance of this dung beetle species—what ecosystem services is it providing when it is removing manure? In particular, we addressed the following questions: (1) How does Canthon humectus affect the health of the soil? (2) Do plants grow better in soils containing dung beetles? To answer these questions, we used 15 pots filled with soil obtained from a semiarid zone in central Mexico. We placed 100 g of manure on the soil, which we weighed daily and replaced with fresh manure. Some pots contained dung beetles (five females and five males). As a control treatment, we placed pots with the same amount of manure but without the presence of beetles. Corn seeds were then planted in all of the pots. We used corn because corn plants grow quickly and, in most arid environments, corn crops are common. At the end of the experiment, we analyzed the soil for activity nitrates, ammonium levels and total soil organic to see if there were differences in the chemical characteristics of soils in our beetle treatment and our control treatment matter and we evaluated the growth of the plants.

In terms of how dung beetles affect soil health, our results showed that, by burying dung, these beetles increase the amounts of nitrogen and ammonia in the soil. Nitrogen is very important for development and is necessary to build enzymes, chlorophyll, nucleic acids, storage proteins, and cell walls, amongst others [2]. Plants take nitrogen up by their roots after soil microbial communities have mineralized nitrogenous compounds to ammonia or nitrate. Low concentrations of these inorganic nitrogen compounds or poor soil microbial activity lead to nitrogenous-deficient plants. To answer our second question regarding plant growth, we examined the corn plants and found that those planted in soils where beetles buried manure grew larger and faster than the plants in soils without beetles did (Figure 3).

Dung Beetles: Improving Soil Health and Helping Plants Grow

In arid and semiarid ecosystems, the days are very hot, the nights are very cold, and all the rain falls during just a few months of the year. In these environments, it is generally difficult for plants to survive. Dung beetles, however, help to improve soil health so that more plants can grow. In our experiments, we found that corn plants grew better in semiarid soils when dung beetles were present. We believe there are several reasons for this. First, our results showed that, by mixing the manure into the soil, dung beetles increase the amount of nutrients in the soil, such as nitrogen and ammonia. We also believe that the presence of dung beetles promotes soil bioturbation because these beetles dig many tunnels throughout the soil [3]. The tunnels give the soil more space to hold oxygen and they also prevent the soil from being packed down too firmly, which inhibits plant growth. Less compact soils can hold more water, so dung beetles help soils to remain moister, as well. We also believe that, if dung beetles do not remove the dung deposited on soils, plants cannot grow because the manure dries up and forms a crust that prevents oxygen from entering the soil. This stops seeds from germinating.

Human beings cannot survive on Earth alone—we rely on many other creatures and the ecosystems services they provide. Think about the important work we just described, all performed by a single species of beetle! This tiny insect can help us to appreciate the often unseen impact that other species can have on our lives.

Glossary

Ecosystem Services: ↑ The benefits that plants or animals provide to an ecosystem, which often improve human health, the economy, and peoples’ quality of life. Examples include pollination and dung removal.

Manure: ↑ Product generated from the digestion of different species.

Semiarid Environments: ↑ Semiarid environments are defined as geographical and ecological units with average annual rainfall of <600 mm and where extreme weather conditions (low rainfall and high temperatures) limit the development of vegetation cover.

Bioturbation: ↑ The reworking of soils and sediments by animals or plants. Bioturbator species have the ability to transport dissolved oxygen, enhance organic matter decomposition and diagenesis, and alter sediment structure.

Acknowledgments

We thank Yureyda Camacho Castillo and Miguel Andrés Pérez Carreón for help with the figures. We thank the ranch owners who allowed us the facilities to work at their cattle ranches.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.