Evolution, or design ?
You might expect dung beetles to keep their "noses to the ground," but they are actually incredibly attuned to the sky. A report published online on January 24 in Current Biology shows that even on the darkest of nights, African ball-rolling insects are guided by the soft glow of the Milky Way.
While birds and humans are known to navigate by the stars, the discovery is the first convincing evidence for such abilities in insects, the researchers say. It is also the first known example of any animal getting around by the Milky Way as opposed to the stars.
"Even on clear, moonless nights, many dung beetles still manage to orientate along straight paths," said Marie Dacke of Lund University in Sweden. "This led us to suspect that the beetles exploit the starry sky for orientation—a feat that had, to our knowledge, never before been demonstrated in an insect."
Dacke and her colleagues found that dung beetles do transport their dung balls along straight paths under a starlit sky but lose the ability under overcast conditions. In a planetarium, the beetles stayed on track equally well under a full starlit sky and one showing only the diffuse streak of the Milky Way.
Dung beetles use stars for orientation
Researchers gave dung beetles caps to block out light. Credit: Marcus Byrne
That makes sense, the researchers explain, because the night sky is sprinkled with stars, but the vast majority of those stars should be too dim for the beetles' tiny compound eyes to see.
The findings raise the possibility that other nocturnal insects might also use stars to guide them at night. On the other hand, dung beetles are pretty special. Upon locating a suitable dung pile, the beetles shape a piece of dung into a ball and roll it away in a straight line. That behavior guarantees them that they will not return to the dung pile, where they risk having their ball stolen by other beetles.
"Dung beetles are known to use celestial compass cues such as the sun, the moon, and the pattern of polarized light formed around these light sources to roll their balls of dung along straight paths," Dacke said. "Celestial compass cues dominate straight-line orientation in dung beetles so strongly that, to our knowledge, this is the only animal with a visual compass system that ignores the extra orientation precision that landmarks can offer."
Dung beetles use their poop balls to cool off.
Have you ever walked barefoot across a sandy beach on a scorching hot summer day? If so, you probably did your share of hopping, skipping, and running to avoid painful burns to your feet. Since dung beetles often live in similarly hot, sunny places, scientists wondered if they, too, worried about burning their tootsies. A recent study showed that dung beetles use their dung balls to cool off. Around noon, when the sun is at its peak, dung beetles will routinely climb atop their dung balls to give their feet a break from the hot ground. The scientists tried putting tiny, silicone booties on the dung beetles, and they discovered the beetles wearing shoes would take fewer breaks and push their dung balls longer than the beetles that were barefoot. Thermal imaging also showed that the dung balls were measurably cooler than the surrounding environment, probably because of their moisture content.
‘Animals produce dung. Certain flies, such as the Australian native bush fly, breed in dung. And dung can also harbour diseases. However, when the correct dung beetles are present, they bury the dung, and problems with flies and disease virtually disappear. Furthermore, in burying the dung, dung beetles fertilize, or manure, the land. This helps the growth of pastures, which then benefits the cattle, sheep, etc., and the farmers! It also means that farmers can use much less of the fertilizers that acidify the soil and add to pollution of watercourses. Dung beetles also tunnel into the soil, providing channels for water infiltration. This reduces water runoff and soil erosion and increases the amount of water in the soil for pasture growth. Dung beetles transform a pollutant into an environmental and agricultural benefit!’
research showed that the humble dung beetles can stop contamination of water supplies with microbes carried by animal faeces. Greg relates, ‘In Milwaukee, USA, in 1993, a Cryptosporidium outbreak caused by contaminated drinking water induced diarrhoea in over 400,000 citizens, killed a few and hospitalized many. In an experiment done in Adelaide, South Australia, in 2003, by a colleague, Dr Bernard Doube, dung beetles removed over 99% of Cryptosporidium spores from a contaminated dung pad on the soil surface.’