Onthophagus taurus

Onthophagus taurus, the taurus scarab, is a species of dung beetle in the genus Onthophagus and the family Scarabaeidae. Also known as the bull-headed dung beetle, it is a species that specializes in cattle dung and is widely utilized to maintain clean pastures, making it agriculturally valuable. These beetles are typically 8–10 millimetres (0.31–0.39 in) in size. The males of this species exhibit distinct characteristics: large "major" males possess long, sweeping, curved horns resembling those of a longhorn bull, while small "minor" males have tiny horns that project upward from the back of their heads. Females, on the other hand, lack horns. These small beetles are oval shaped, the color is usually black or reddish brown. Sometimes the pronotum has a weak metallic sheen.

Onthophagus taurus originally inhabiting areas characterized by a Mediterranean climate, is native to central and southern Europe as well as Asia Minor, spanning from Spain to Morocco, Turkey, and Iran. It was introduced to the United States and Australia in the late 1960s to early 1970s to help manage cow dung. This introduction aimed to displace dung from cattle pastures underground, thereby, promoting soil health and pest control. They are most abundant in grassland habitats because cows reside. This species is now present in Australia, Europe, Morocco, Algeria, Tunisia, Syria, Iraq, Transcaucasia, Asia Minor, Iran, Afghanistan, Central Asia, and the United States of America.

Onthophagus taurus was accidentally introduced in the eastern United States. It was initially sighted in Florida in 1971, and later in the northeast United States. Based on the population size and spread pattern, it is suggested that O. taurus likely entered the United States from the coastal area of Florida. Subsequently, the US Department of Agriculture deliberately released O. taurus in various locations, including California, Texas, and New Jersey, resulting in a substantial increase in range from where it was first introduced.

O. taurus develops most optimally between 16 °C and 23 °C. As a result, its reproductive success is limited in extremely cold regions, restricting its distribution there. In 1974, Onthophagus taurus was introduced to Australia, collected from populations in Spain, Greece, and Turkey. It quickly became the most prevalent exotic species in southwestern Australia within two years of its introduction. It has even displaced O. binodis as it arrived initially, overtaking this earlier-introduced dung beetle species across Australia.

Onthophagus taurus females fly to fresh dung pads and use their mandibles to excavate tunnels into the soil below. These beetles spend days sorting through manure and arranging it throughout the tunnel. The female then carefully constructs the brood chamber using her saliva. Subsequently, they move dung down to the ends of the tunnel where they pack dung into oval brood balls, and they roll them into the dug-out brood chamber. This nesting area houses several brood balls approximately 10 – 15 cm below the surface. One egg is laid inside each brood ball where larvae would complete their development within these buried balls of manure. By storing the dung underground, it stays fresh and protects the developing grubs from predators and parasites. Adult males enter the dung pad to feed and mate. Both males and females assist in offspring provisioning. A male's primary role is to transport dung from the surface and deliver it to the female in the brood chamber, while the female's primary role is to incorporate this dung into the brood balls.

The entire juvenile portion of the beetle's life cycle occurs in the brood ball. After the larva is hatched from the egg, it typically consumes 40 - 55% of the dung ball as it develops and grows. Afterward, larvae pupate inside a pupation chamber made from late larval fecal matter and leftover brood ball material, within the remains of the brood ball. Upon completing the pupal stage, the beetle becomes a fully developed adult. In the final phase of the dung beetle's life cycle, adults are ready to relocate to a fresh dung pad to initiate the cycle once more. They must then locate a mate for pair bonding and begin the process of preparing a new nesting environment.

Male Onthophagus taurus exhibit two distinct morphs: When males exceed a critical body size, they develop a pair of long curved horns on their heads, otherwise known as large, "major" males. Smaller males remain hornless—they are known as "minor" males. Although horn size in these beetles may not be strongly heritable, the quantity of food parents supply for their larvae significantly impacts beetle morphology. Previous research indicates that both offspring size and horn length are primarily determined by the amount of dung provided to developing larvae. Moreover, isolated groups of O. taurus have exhibited variations in the shape of their fore-tibiae, a trait linked to soil density and the depth at which they dig and nest.

This is an example of polyphenism, a phenomenon where organisms with the same genetic makeup exhibit different physical traits in response to environmental factors. In the case of O. taurus, if the larva grows to a size above or below a genetically determined threshold, its development changes. More specifically, the growth of horns increases or decreases, respectively, in response to this environmental reprogramming.