DUNG BEETLE: CHARACTERISTICS, HABITAT, FEEDING - BIOLOGY - 2024

The dung beetles are animals belonging to the Coleoptera order and Scarabaeoidea superfamily. The specimens feed mainly on the feces of multiple species of mammals.

Some species mold the feces with their legs, until it acquires the shape of a homogeneous ball, which they will transport to the desired site. They can carry feces that exceed their own weight by orders of magnitude. Others are capable of tunneling underground.

Source: Axel Strauß

They are a key element in maintaining optimal soil quality, since they actively participate in the cycling of nutrients. At the same time, when the animal eliminates excess feces from the ecosystem, it helps to reduce flies and other unwanted animals.

In addition to the ecosystem services they provide, dung beetles have distinguished themselves in human society from a cultural point of view. They have been important species for various civilizations, highlighting the Egyptians who glorified the image of these beetles.

characteristics

Dung beetles are a group of species belonging to the Scarabaeoidea superfamily. Compared to the other beetles, they are medium to large in size.

The trait that characterizes them is the consumption of excrement produced by warm-blooded animals and molding it with their front legs into easily transportable balls. However, not all species exhibit this behavior. Some species can form tunnels.

Depending on the ability to form tunnels or to stack balls of excrement, dung beetles are classified in Anglo-Saxon literature under the terms of tunnelers and rollers, respectively. A third group does not exhibit any of the behaviors described and are called dwellers.

The excrement not only serves as food for this wide range of coleoptera species, it will also serve as a site for courtship and reproduction.

Among the outstanding members we have the species Scarabaeus satyrus, which according to the evidence is the only invertebrate capable of orienting itself using the Milky Way.

Habitat and distribution

Dung beetles are found on every continent on earth, with the exception of Antarctica. They can live in different types of ecosystems, including deserts, forests, savannas, grasslands, and farmland.

Taxonomy

Beetles are members of the class Insecta and are represented by a quarter of all the animals described so far, with more than 300,000 species belonging to the order Coleoptera, making it the taxon with the most species on the entire planet earth.

One of the largest groups within Coleoptera is Scarabaeoidea, with more than 35,000 known species. In addition to the dung beetles, the group includes other types of beetles. Note that there is not a single species of dung beetle, this is a term that is applied to thousands of species of the Superfamily Scarabaeoidea.

Currently there are about 6,000 species of dung beetles, distributed in more than 257 genera. This success can be attributed to their mobility, as most species can fly and their life limit is relatively low.

Evolution and phylogeny

According to the evidence, the divergence between the Aphodiinae groups (another group of beetles that also feeds on excrement) and Scarabaeinae occurred about 140 million years ago between the Jurassic and Cretaceous.

Preliminary studies have used the molecular clock to estimate the origin of the dung beetles, and the group appears to date back 110 million years. However, other authors propose that the group emerged 56 million years ago - a considerable difference from the previous data.

One of the first identified fossils has been Prionocephale deplanate, which lived about 90 million years ago in the Cretaceous.

It is speculated that the first dung beetles were probably small animals with elongated bodies, similar to members of their sister group, Aphodiinae.

Feeding

One of the most representative features of the group is its diet based on animal excrement, a trophic habit known as coprophagia. Current species mainly consume the feces of herbivorous mammals or omnivores. This feeding pattern is shared by the adults and the larvae.

The animal can find its food by making use of a refined sense of smell that will help it to quickly find the excrement. The excrement represents an item of high nutritional value for the beetle, since it is rich in bacteria, nitrogen, complex carbohydrates, vitamins and minerals.

Since there are multiple species of dung beetles in a single ecosystem or area, the interspecific competition is usually quite high, so there are multiple ecological variants of these coleopterans.

Evolution of coprophagia in dung beetles

This trophic pattern could have evolved from a saprophagous ancestor or from a diet based on fungi - a diet that is still retained by the sister group of these beetles. With the radiation from the mammals, the beetles were able to co-radiate and diversify with them.

With "radiation" we mean to refer to an evolutionary concept in which a great variety of species appear in a short time. With the appearance of multiple species of mammals, the beetles had a new range of possible niches, in trophic terms, and were able to radiate.

Surprisingly, dung beetles exhibit a unique activity pattern: their flight periods are correlated with the defecation patterns of mammals, although some are nocturnal.

Reproduction

Courtship and sexual selection

Recognition between individuals of the same species is the first step for reproduction. Both males and females are present in the fresh stool, where courtship begins.

The Scarabaeoidea superfamily is characterized by having secondary sexual traits in males. Naturalist Charles Darwin was the first to note the extraordinary radiation of these characteristics and the general pattern of sexual dimorphism in beetles.

To explain the existence of these exaggerated arbitrary traits in many species (not just beetles) Darwin proposes the theory of sexual selection, which today has robust supporting evidence.

The most notable feature is the horn of the males. This can be present in females, but only in a rudimentary way. Its owner uses them in male-male combat.

In addition to morphological characteristics, males secrete a series of pheromones that appear to be involved in inter-species courtship and recognition.

Eggs and metamorphosis

Females have only one ovary that allows a single ovary. When the female is ready, she lays her egg in a chamber built for this purpose. The eggs of the dung beetles are laid on the excrement, and the way they do so varies depending on the species.

The larva emerges from the egg after one to two weeks and feeds on the excrement where it hatched. After about 12 weeks the individual is considered a pupa, and after one to four weeks it is an adult.

Depending on the species, there may be periods of diapause (a kind of hibernation in insects) in any of the states mentioned. This adaptive behavior allows the organism to survive when environmental conditions are not suitable for its development.

In the pupal stage, the individual requires adequate nutrition for the total remodeling of the body to occur and the development of complex structures that will form part of the adult.

Parental care

Parental care is a widely distributed behavior among dung beetles, where both the female and the male are active participants.

Both parents embark on a search for excrement to accommodate the chambers where the calf will be born. However, in some species such as Onthophagus parental care is restricted to males.

This aspect is one of the most expensive - in terms of time and energy - of reproduction. Due to these high costs, a female has few offspring and it is estimated that the average number of offspring per female per year is 20.

Ecological importance

Dung beetles are biological entities that play a number of indispensable roles, both in tropical forests and in other ecosystems. Thanks to the ecosystem services that these beetles provide, they have gained the attention of various researchers worldwide.

As their main source of food is excrement, they are involved in the nutrient cycle and consequently shape the structure of the soil. In some areas, it has been proven that the presence of the beetle significantly improves the nutritive content of the soil.

In addition, they participate as secondary seed dispersers. As the animal only consumes the excrement, it is a good dispersal agent for the seeds that have been trapped in the excrement. After releasing the seeds, they can continue their germination process.

The rapid removal of feces by the beetle prevents the accumulation of flies and other animals that can be potential vectors of disease for livestock. That is, they contribute to hygiene.

Thanks to these benefits, some countries (including Australia, Hawaii, North America, among others) have sought to introduce different species of dung beetles to their lands, seeking to increase the quality of the soil and reduce the population of local flies.

References

1. Castro, EC, & Martínez, AP (2017). Reproductive behavior of dung beetles (Coleoptera Scarabaeidae) under laboratory conditions. Journal of Agricultural Sciences, 34 (1), 74-83.
2. Hanski, I., & Cambefort, Y. (2014). Dung beetle ecology. Princeton University Press.
3. Resh, VH, & Cardé, RT (Eds.). (2009). Encyclopedia of insects. Academic press.
4. Scholtz, CH, Davis, ALV, & Kryger, U. (2009). Evolutionary biology and conservation of dung beetles. Pensoft.
5. Simmons, LW, & Ridsdill-Smith, TJ (2011). Ecology and evolution of dung beetles. John Wiley & Sons.