These Beetles Are Specialized Fighters

Like the swords of warriors in a bygone age, researchers have found that male rhinoceros beetles have different shaped horns to complement various fighting styles. According to a recent study, these styles differ from species to species, and can characterize how a beetle holds its own in battle.

The study, published in the journal Proceeding of the National Academy of Sciences, details why exactly so many different horn types evolved for what is considered one of the strongest animals in the world (if not THE strongest).

Past studies and this one alike found no evidence that sexual selection - that is, females choosing males with specific characteristics - determined horn shape. So Erin McCullough of the University of Montana at Missoula and her colleagues theorized that horn shapes evolved to determine fighting ability.

Using a computer modeling system, the researchers looked at various horn types to determine what kind of stresses they can withstand and in what way. Three species in particular were studied - Trypoxylus dichotomus, Golofa porteri and Dynastes hercules - each of which has a very differently shaped horn. (Scroll to read on...)

Interestingly, they found each horn has its own very unique style of battle, much like different classes of swords.

Trypoxylus, with a pitch fork-like horn, pries and twists at its opponents, dislodging them from tree territory (usually tree trunks). The Golofa, with a long and slender horn, uses it almost like one prong on a fork lift, sliding under its opponent to easily throw off their balance. And the twin horns of the Dynastes form pincers, allowing the beetle to grip its opponent and literally throw it away.

As expected, cross sections of these horns showed structures that catered specifically to these varied styles of combat, in which the least stress was applied to the horn if used as it was intended.

The authors of the study concluded that their work "establishes a critical link between weapon form and function, revealing one way male-male competition can drive the diversification of animal weapons."