Jump? Still jumping? If you jump again, you will... go to hell!

Speaking of dung beetles, everyone may be familiar with them. Dung beetles belong to the subfamily of the family Scarabaeidae in the order Coleoptera. This insect, with a "smell" in its name, usually appears to be "meticulously rolling dung balls with its head down".

Although they have a bad reputation, as tireless scavengers in nature, dung beetles are of unquestionable importance in the ecosystem.

A dung beetle rolling a dung ball. Copyright image, no permission to reprint

However, in addition to being a scavenger in nature, dung beetles are also regarded as "scarabs" by the ancient Egyptians, and they even possess the magical skill of "observing the sky and knowing the direction."

01

The Scarab That Pushes the Sun

Scarab? Pushing the sun?

After seeing these two descriptions, many of my friends will certainly feel confused. Aren’t dung beetles pushing dung balls? When did they become associated with the word "holy" and can even push the sun?

It all started with the mythology of ancient Egypt.

Herodotus, an ancient Greek historian, once said that "Egypt is a gift from the Nile". Thousands of years ago, the ancient Egyptians lived in the narrow Nile River basin, working from sunrise to sunset. But the ancient Egyptians were not the only ones who thrived in this land nourished by the Nile River. When the ancient Egyptians worked in the fields, they often saw a large black beetle tirelessly rolling a black ball that was much larger than itself.

The Nile River. Copyright image, no permission to reprint

In the eyes of the ancient Egyptians, the sphere is a symbol of the sun in the sky, and the beetle that can make the black sphere must have been instructed by the gods to create such a "exquisite" creation, so the ancient Egyptians called this large black beetle, also known as the dung beetle, a "scarab."

Ancient Egyptian scarab ornaments. Image source: historicaleve.com

The ancient Egyptians believed that the movement of dung beetles rolling black balls (dung balls) symbolized the rising and setting of the sun. Therefore, in ancient Egyptian mythology, there was a scarab god called Khepri, and the statue of Khepri usually had a scarab head, symbolizing the sunrise.

The scarab god in ancient Egyptian mythology. Image source: historytoday.com

In addition to symbolizing sunrise, the scarab god also represents rebirth, because most dung beetles lay their eggs in dung balls. When their offspring break out of the dung balls and are observed by people, a more wonderful association is born: the scarab brings hope for rebirth. It is precisely because of this association that people began to make ornaments in the shape of scarabs and put them on the chests of the deceased and buried with the deceased, hoping that they can be reborn like the scarabs.

Today, although people have realized that it is impossible for a giant "scarab" to push the sun to rise and set in the sky, some interesting behaviors of this big black beetle have attracted the attention of many scientists.

02

The Scarab That Pushes the Sun

Relying on the sun to point the way

Everyone may know that dung beetles roll dung balls every day, but many friends don’t know that they mostly do this work along a straight line (not completely straight, there is a certain deviation). Yes, dung beetles do not simply roll dung balls along the terrain, but have a purpose and direction!

This is not nonsense. There are scientists who have studied this issue. They recorded the trajectory of dung beetles rolling dung balls and found that dung beetles have an extremely strong desire to transport dung balls in a straight line. If there are obstacles on the route that cannot be directly crossed, they will bypass the obstacles and then return to the original straight route.

Scientists are recording the path of dung beetles transporting dung balls. Image source: Reference [2]

This ability to keep moving straight is undoubtedly amazing. After all, as people with poor directions, we humans can easily get lost in the desert or in dense forests and go around in circles. If we were blindfolded, we would just keep going around in circles in a small circle with a diameter of less than 20 meters. So, how do dung beetles keep moving in a straight line?

The mystery is actually related to the sun.

According to scientists, during the day, dung beetles use the sun as a compass. Although the sun is not motionless in the sky, it only takes a few minutes for dung beetles to move their dung balls, so in a short period of time, the sun can be used as a reference coordinate for positioning. When scientists cover the eyes of dung beetles, since they cannot see the sky, the movement trajectory of dung beetles is completely messed up. Their journey is no longer in a straight line. Sometimes they return to the starting point, and sometimes they take many detours.

After being blinded, the dung beetle's tracks became chaotic. Image source: Reference [2]

Similarly, if a green LED light is used to simulate the sun and placed in the opposite direction, the dung beetle will also take corresponding actions and turn around and walk straight in the opposite direction.

In other words, the scarab not only did not push the sun to rise in the east and set in the west, but it was the sun that guided the direction of the scarab's movement.

Although the ancient Egyptians' imagination was not correct, dung beetles do have a close connection with the sun.

03

Many ways to give directions

Do a mysterious dance before pushing the dung ball

Dung beetles have many ways to determine the direction of their dung balls, not just relying on the sun. After all, the sun may not be visible on cloudy days, and it may not be visible at all at night.

So, what should the dung beetle do in this situation?

Smart dung beetles are naturally not helpless, they use polarized light for orientation. You may not believe it, but scientists have found that dung beetles may record a snapshot of the sky at the beginning of their dung ball rolling journey. This snapshot records the pattern of polarized light in the current area. When the dung beetle finds that the polarized light pattern in front of it is different from the memory in its brain, it will stop and turn around, find the direction consistent with the snapshot in its mind, and then roll the dung ball to the destination.

Speaking of this positioning method, we have to mention the mysterious dance that dung beetles perform around the dung ball before transporting it.

The mysterious dance of dung beetles. Video source: Reference [2]

In the video, a dung beetle stopped in front of a completed dung ball. Instead of rushing to start its journey, it climbed onto the dung ball, turned a full circle on top of the dung ball, and then got off the dung ball and pushed it out of the screen.

The mysterious dance of dung beetles. Image source: Reference [2]

Scientists believe that this dance before pushing the dung ball is the process of dung beetles taking snapshots of sky features. By turning 360 degrees on the dung ball, dung beetles can fully record all available celestial features in the sky and polarized light patterns in the environment. This allows them to not get lost without the sun as a reference point.

The mysterious dance of dung beetles is actually recording the polarized light patterns around them. Image source: Reference [5]

When the sun sets, the moon becomes the magic weapon for dung beetles to orient themselves. The compound eyes of dung beetles have high optical sensitivity, allowing them to use the moon for orientation at night. Not only that, when the moon cannot be seen at night for some reason, the shining Milky Way in the sky can point the way for their journey. Dung beetles are the only known animals that use the Milky Way for short-range linear orientation. Isn't it amazing?

The sophisticated compound eye structure of a dung beetle. Image source: Reference [2]

The tiny dung beetle rolls dung balls and acts as a scavenger of the ecosystem, but it has dreams and moves forward straight ahead. As it moves forward, it only has the sun, moon, stars and the universe in its eyes. Who can say that it is not a scarab?

References:

[1] Byrne, M., Dacke, M., Nordström, P., Scholtz, C., & Warrant, E. (2003). Visual cues used by ball-rolling dung beetles for orientation. Journal of Comparative Physiology A, 189(6), 411-418.

[2] Dacke, M., Baird, E., El Jundi, B., Warrant, EJ, & Byrne, M. (2021). How dung beetles steer straight. Annual review of entomology, 66, 243-256.

[3] Souman, JL, Frissen, I., Sreenivasa, MN, & Ernst, MO (2009). Walking straight into circles. Current biology, 19(18), 1538-1542.

[4] Foster, JJ, El Jundi, B., Smolka, J., Khaldy, L., Nilsson, DE, Byrne, MJ, & Dacke, M. (2017). Stellar performance: mechanisms underlying Milky Way orientation in dung beetles. Philosophical Transactions of the Royal Society B: Biological Sciences, 372(1717), 20160079.

[5] El Jundi, B., Foster, JJ, Khaldy, L., Byrne, MJ, Dacke, M., & Baird, E. (2016). A snapshot-based mechanism for celestial orientation. Current biology, 26(11), 1456-1462.

Produced by | Science Popularization China

Author: EVEE School of Life Sciences, Peking University

Producer｜China Science Expo

Submitted by: Computer Information Network Center, Chinese Academy of Sciences

The cover image and the images in this article are from the copyright library

Reproduction of image content is not authorized