A rhinoceros beetle that is active at night and early in the morning in thickets of trees in summer.


Originally thought to be nocturnal, a researcher from Yamaguchi University has discovered that it may actually be forced into nocturnal behavior by a powerful rival.

Rhinoceros beetles are among the largest of the insects that appear in thickets in summer, and have been considered one of the strongest insects in the fight over the sap they feed on.



Wataru Kojima, a lecturer at the Faculty of Science, Yamaguchi University, who is familiar with the ecology of beetles, observed beetles gathering in tree sap in a sawtooth oak forest in Yamaguchi City in the early morning of August this year.



Kojima successfully observed and photographed the giant hornet repeatedly biting the leg of the beetle and throwing it down one after another, monopolizing the sap.

This was confirmed around 5:00 in the morning over three days, and in each case the giant hornet hijacked the sap in just a few minutes.



To see how the beetles' activity would change in the absence of the giant hornets, they removed the beetles with a bee-repellent spray, and more than half of the beetles remained in the sap until at least noon.

From these results, we analyzed that beetles, which were originally thought to be nocturnal, may be forced to be nocturnal to avoid giant hornets, which are not active at night.



Mr. Kojima said, "I think I was able to gain a new perspective that animals that were originally thought to be nocturnal may actually become nocturnal for some reason." talking

The spectacle of the offense and defense "shock" over the sap...

A five-minute video shot early this August in the suburbs of Yamaguchi City by Wataru Kojima, a lecturer at the Faculty of Science at Yamaguchi University, clearly captures the fight between beetles and giant hornets over the sap of the sawtooth oak that they feed on. I'm here.



Around 5 am, about 10 male and female beetles were clinging to the tree and sucking the sap.

There, several giant hornets, which became bright and became active, flew in.



Once perched on the trunk, the giant hornet approaches the sap-sucking beetle from the side or behind and targets its legs.

It bit the leg again and again and dropped one beetle after another from the tree.



Some of the beetles stopped sucking the sap and confronted the giant hornet from the front, but this time, multiple wasps bit their legs from the sides and back at the same time, and they just fell down.



It took only 3 minutes for the beetles to disappear from the sap feeding area.

After that, giant hornets dominated the feeding grounds.

Kojima, a lecturer at the Faculty of Science at Yamaguchi University, who took the photo, said,


"It's a strong beetle, but when it's bitten by its legs, it loses its clinging power and becomes unable to resist. I had thought that beetles, which are heavier and have harder bodies, would have an advantage over giant hornets when it came to competing for food, but I was shocked to see them being so easily thrown down by the hornets.”

Experts: “Evolutionary process: more detailed verification”

Kunio Aratani, a professor at Kyushu University's graduate school who is familiar with the biodiversity of insects and other organisms, says, "Rhinoceros beetles have been considered the king of the insect world, and their natural enemies include birds and humans that are larger than beetles. It has been thought that they are mammals, but the result of this study is that the giant hornet might actually be stronger than the beetle. However, it is very interesting to see that the bee knows the weakness of biting its leg and throws it off with that, as it seems to show the cleverness of the bee."



On the other hand, regarding the possibility that Asian giant hornets are forcing beetles to be nocturnal, I wondered, "How are the behavioral hours of beetles changing in areas where giant hornets do not exist, and to what extent are other natural enemies such as birds affecting them?" It is necessary to examine the evolutionary process in more detail, including whether or not