Why can dung beetles walk in a straight line in the dark when they push dung balls backwards?

Dung beetles push dung balls in a straight line, which can leave the dung source as quickly as possible and never come back. If it goes in the wrong direction and pushes the dung ball back to the dung source, other partners will stop the rolling dung ball at hand, come and hit it and take the rounded dung ball away.

Walking in a straight line is the best strategy for dung beetles to keep the fruits of their labor. In the forest under the scorching sun, dung beetles left the dung source and pushed the ball upside down with his hind legs. Although it is upside down, it keeps walking in a straight line, and it doesn't change direction when going uphill or downhill. The rolling dung ball suddenly hit a stump and deviated from the route.

The dung beetle stopped, jumped on the dung ball and danced to the sun for a while. The ancient Egyptians believed that the dung beetle was seeking the guidance of the sun god when it got lost, and the sun god always cared about it and pointed it out in the right direction every time. The dung beetle blessed by the sun god had a name called scarab in ancient Egypt, and its behavior of pushing dung balls symbolized the movement of planets in the sky.

The dung beetle guided by the sun began to push the dung ball again. At this time, the dung ball returned to its original direction and continued to walk in a straight line.

When the sun goes down and the moon rises, the dung beetle jumps on the dung ball after encountering obstacles, dances to the moon, then returns to the original direction and continues to walk in a straight line. Not only the sun god, but also the moon god pointed out the right direction for it.

You can walk in a straight line in the sunshine and moonlight. You determine your direction according to the position of the sun and the moon in the sky, while dung beetles determine your direction according to the polarized light of the sun and the moon in the sky. Dung beetles, favored by the sun and the moon, can see polarized light that you can't see.

When sunlight and moonlight pass through the atmosphere and are refracted by water vapor and particles in the air, a pattern diverging around celestial bodies will be formed in the sky, which is called celestial polarized light. Simply put, the propagation of natural light in all directions is uniform, while the propagation amplitude of polarized light in all directions is different, strong and weak. Celestial polarized light can be seen that there are light and dark differences in different propagation directions.

When the dung beetle jumped on the dung ball, he looked up for the sun. He rotated several dance steps on the dung ball, adjusted his angle with the help of the polarized light of the sun, and after aiming at the angle, he could continue to push the dung ball in the original direction. Although the light of the moon is one million times darker than the sun, the dung beetle (Scarabaeus zambesianus) can also see the polarized light of the moon and adjust its direction according to the moonlight.

Why do dung beetles determine their position according to polarized light instead of the position of the celestial sphere? The team of Lund University in Sweden did an experiment. In the moonlight, Zambezia dung beetle was given a pair of filter glasses, and the polarized light direction of the moon was changed by the filter. The black dot in the picture above is when the dung beetle is fitted with a filter. In the next journey, the dung beetle changed its walking direction and deviated 70 degrees to the right. When the filter is removed, the dung beetle will walk back in the right direction

The sun and the moon are bright single celestial bodies, and dung beetles can distinguish polarized light from celestial bodies. In the sky full of stars, the stars twinkle, the light reflects each other, and the polarized light of a single celestial body loses its function. Can dung beetles get lost without the guidance of celestial polarized light? No, it can go straight.

Dung beetle under the starlight

In the dung beetle population, some teams are active during the day. For example, the dung beetle in Zambia likes to move during the day and at the beginning of the first month. There are other teams in the group, such as S.satyrus.

The team designed a circular venue for the dung beetle's night trip, put the dung beetle in the center of the circle, and recorded the time when it walked out of the venue without the moon and only the starlight. If it only walks in a straight line, it will walk out of the venue soon, and if it detours, it will not walk out for a long time.

When there is a moon, dung beetles comes straight out of the ground. The picture on the left shows that when there is no moon but starlight, its path is not so straight, so it takes a little more time to go out. The team put a paper hat on dung beetles, blocking his view of looking up at the starry sky. Only at the foot of dung beetles got lost and walked a lot of detours to get out of the meeting. The middle picture shows the dung beetle route map after the starry sky is covered.

Why can dung beetles tell directions under the starlight? Can it read constellations and identify positions by observing stars? The team took dung beetles who walked at night to the Johannesburg Planetarium to see the starry sky. On the ceiling of the planetarium dome, there are 4000 stars and the Milky Way. Dung beetles participate in the test in five situations, 1, with 4,000 stars and a complete starry sky in the Milky Way; 2. Only the Milky Way; 3. Remove 18 brightest stars, leaving only other dim stars; 4. The brightest stars are only 18; 5, all black.

The left picture shows the field test results, and the right picture shows the test results in the planetarium. Under the complete starry sky, dung beetles perform as well in the planetarium as in the wild. Only in the Milky Way, it takes a little more time to play. When there are only 4,000 dim stars, there is a little more time to walk out of the venue. If there are only 18 stars, then its performance is very bad.

Planetarium test proves that dung beetles can't read constellations and can only look at stars. Guided by the starry sky or the bright milky way, it can find the right direction.

Dung beetles won the 20 13 Ig Nobel Prize for their experimental research on understanding the Milky Way and stars. It is funny to take dung beetles to the planetarium to see the stars, but it is of great significance. This is the first time to locate insects by stars.

Dung beetles only push dung balls in a straight line and can be illuminated by the sun, moon and stars.