Deceptive Vibratory Communication Helps Protect Pupal Cells of Japanese Rhinoceros Beetles

The Japanese rhinoceros beetle is a group-living beetle that spends the majority of its life (sometimes up to two years) developing underground before emerging from the soil as an adult beetle. Found throughout Asia, it is popular in gambling where bettors wager on the survival of their favorite beetle. Two males are placed together near a female beetle, and sensing a chance to mate with her, they will engage in ferocious battle using their specialized "horns" until only one is left.

The rhinoceros beetle goes through several distinct life stages before reaching adulthood. Eggs are laid in the soil by the adult female just before she dies. The eggs hatch and the worm-like larvae feed on wood and other vegetation in the soil. Next, each larva builds a specialized structure called a pupal cell, in which it will undergo the next life stage as a pupa. The pupal cell is constructed from soft soil, or hummus, vegetation, and faecal pellets. Once finished, the larva is encapsulated in the pupal cell where it becomes a pupa, and then transitions into its adult (beetle) form over the course of several months. The beetle breaks out of the pupal cell and makes its way towards the surface where it will live above ground for a few months before mating and dying.

Because of its group-living social structure, hundreds of rhinoceros beetle larvae can be feeding and burrowing in the soil among already-completed pupal cells. There is a high risk that some larvae may collide with one of these delicate structures and fatally interrupt pupation. In order to deter burrowing larvae, pupae emit strong vibrations that cause a "freeze response" in the larvae, and stops them in their tracks. Researchers believe that pupae have taken advantage of the larvae's response to vibrations, which are most commonly given off by the their natural predator, the mole. Pupae exploit the freeze response by mimicking the vibrations produced by moles, and repel nearby larvae. This is an example of what researchers call "deceptive vibratory communication" and it is used by several other species of group-living insects that make delicate underground pupal cells.