Dung beetles navigate the Milky Way

(ORDO NEWS) — Entomologists have made an amazing discovery. Nocturnal dung beetles (Scarabaeus satyrus) can navigate the Milky Way.

Although the beetle’s compound eyes cannot distinguish individual stars, this species can see the Milky Way as a streak across the sky and perhaps even distinguish features such as the galactic center and stardust lanes.

“Currently, dung beetles are the only animals known to us that use the Milky Way for reliable orientation,” says James Foster of the University of Konstanz in Germany. “They’re great little astronomers.”

A short story about dung beetles: They are nature’s orderlies. Whenever a pile of waste appears in the forest, dung beetles flock to clean up. Each beetle makes a ball of dung, which it rolls in a straight line. Away from the pile, the ball will be buried and eaten, and is sometimes used as bedding for dung beetle eggs.

Sounds simple, but there is a problem. Dung beetles are aggressive. If two bugs emerging from the pile collide with each other, they can engage in a vicious fight that often ends in judo-style full-body overhead throws.

Wandering in circles (as people who get lost do) increases the chances of a fight even more. Therefore, dung beetles have developed the ability to quickly move in a straight line to a safe place.

During the day they are guided by the sun. Dung beetles see polarization patterns in the daytime sky and use them to keep their course. One patch of blue sky is enough. This trick also works at night.

Dung beetles are the only creatures known to be able to see moonlight polarization, which is 100 million times weaker than daytime polarization. Research shows that dung beetles walk in a straight line at night just as accurately as they do during the day, even if the moon is a weak crescent.

But what happens when there is neither the Sun nor the Moon? In the early 2000s, this question worried two dung beetle researchers, Eric Warrant and Marie Dacke of Lund University in Sweden.

To find the answer, they took some beetles to the planetarium at the University of the Witwatersrand in Johannesburg, South Africa, and projected the Milky Way onto a domed ceiling. The beetles saw him and took their bearings.

Their discovery caused a real explosion in dung beetle research. James Foster is a leader in this field and publishes new results every few years.

Dung beetles navigate the Milky Way 2

Foster and his colleagues built a rudimentary planetarium specifically for dung beetles. It uses LED lights to mimic the Milky Way that beetles see with their compound eyes.

In 2017, they found that dung beetles are able to distinguish between the northern and southern arms of the Milky Way, sensing an intensity contrast of up to 13%.

This threshold makes objects such as the galactic center in Sagittarius and the Great Rift in Signus (dark dust clouds located close to the Solar System, significantly covering the central region of the Galaxy and most of the plane of the Milky Way for an earthly observer), theoretically accessible to the perception of beetles.

Then they added city lights to the experiment – and the results weren’t very good. “Light pollution may be causing beetles to abandon the Milky Way as a compass,” Foster worries.

In a paper published in July 2021, Foster’s team described how urban lighting destroys the Milky Way, reduces moonlight polarization by 60-70%, and “creates man-made celestial clues.”

The last point is the worst of all. Spotlights and brightly lit buildings mesmerize the beetles, who suddenly ignore the sky and rush towards the man-made lamps.

“These beacons attract beetles to the most hostile areas of the environment,” says Foster. “After rolling their balls for some distance, the beetles should find a patch of soft sand where they can burrow.

They are unlikely to find it in close proximity to bright artificial lighting, whether in cities or rural areas, since it is usually associated with concrete and asphalt” .

Dung beetles are not the only ones. The researchers believe they have only just begun to explore this area, which has potentially thousands of species observing the stars. These representatives of our ecosystem can be influenced by everything from simple light bulbs to modern space satellites.


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