A species of horned beetle has a startling secret: a gearing mechanism in its mouthparts. The beetles beat us to the invention of meshed gears, possibly by millions of years.
Japanese rhinoceros beetles (Trypoxylus dichotomus) are found in east Asia. Males can be 8 centimetres long. This is unusually large for an insect, although not as large as male that can reach double the size.
In Japan, the rhinoceros beetles are popular pets and are regularly depicted in anime and other media. 鈥淭here is nobody who has not touched the horned beetle in Japan,鈥� says at the Tokyo University of Agriculture and Technology in Japan.
Advertisement
Abe鈥檚 team was studying the beetles鈥� genetics when their breeding programme created some with abnormally-shaped heads. To figure out exactly what was unusual, they needed to know what the mouthparts or 鈥渕andibles鈥� of normal beetles looked like.
Surprisingly, this had never been documented. So Abe鈥檚 colleague Wataru Ichiishi 鈥╠issected some and was startled to discover that the right and left mandibles moved simultaneously.
A closer examination revealed that each mandible has two gear teeth, and the two sets mesh. As a result, when one mandible moves, so does the other.
A bug鈥檚 life
Abe thinks the gearing has evolved because of the beetles鈥� lifestyle. They spend a lot of time chewing the tough bark of trees to feed on sap.
If one of the mandibles broke, the beetle might starve. Linking the two mandibles with gears spreads the force between them, reducing the strain on each mandible and making it less likely to break.
Surprisingly, given how well known rhinoceros beetles are in Japan, the gears do not seem to have been described before. 鈥淲e checked a large number of old books and magazines,鈥� says Abe.
What鈥檚 more, it seems Japanese rhinoceros beetles are not the only rhinoceros beetles with gears. There are eight 鈥渢ribes鈥� of . Abe鈥檚 team found gears on the mandibles of species belonging to five of them, and they have tentative evidence from the other three. However, 16 beetles from other groups did not have the gears.
鈥淎pproximately 1700 species of horned beetles have been identified globally,鈥� says Abe. 鈥淲e think these gear structures are common to all horned beetles.鈥� That implies the group has had gears for a long time, well before humans devised them.
This is the second instance of gearing mechanisms being found in nature. In 2013, Malcolm Burrows at the University of Cambridge discovered that Issus coleoptratus, a kind of jumping insect called a planthopper, had meshing gears on its legs. These seem to help the insect synchronise its leg movements and thus jump further.
ZooKeys
