The dung beetle is now the first animal proven to use the light of the Milky Way for orientation and navigation, thanks to new research from Wits University. The vast and dim milky glow of our home galaxy apparently provides a good source of orientation when the Sun or a bright Moon isn’t available (or meteor showers for that matter).
Dung beetles don’t have eyes that are sharp enough to clearly distinguish between exact constellations (from our current understanding of their eyes). They rely on the overall gradient of light to dark, that the light of the Milky Way provides, to get a sense of orientation. This allows them to make sure that when they are harvesting dung from a dung pile, that they continue moving away from it instead of accidentally circling back into their competitors.
“The dung beetles don’t care which direction they’re going in; they just need to get away from the bun fight at the poo pile,” claims Professor Marcus Byrne from Wits University.
The researchers have previously published other findings on the dung beetle, including proving that dung beetles make use of the Sun, the Moon and polarised light for orientation and navigation.
For the first experiments, the dung beetles had their eyes covered up and blocked with “caps”, and were then observed. During the research, a seemingly new behavior was also discovered. The dung beetles were observed climbing to the top of their dung balls, and then using the higher position to locate the sources of light that they then used for orientation, the researchers labelled it as a “dance”.
To follow up on that first research, further experiments were then conducted under the simulated light and night sky of the Wits Planetarium. In the planetarium, the beetles were very clearly shown to be using the Mohawk of the Milky Way for orientation and navigation.
“We were sitting out in Vryburg (conducting experiments) and the Milky Way was this massive light source. We thought they have to be able to use this — they just have to!” said Byrne.
“Not all light sources are equally useful landmarks for a dung beetle. A moth keeping a constant angle between itself and a candle flame will move in a circle around the flame. However, a celestial body is too far away to change position relative to a dung beetle as it rolls its ball, with the result that the beetle keeps travelling in a straight line.”
It’s very likely that the dung beetles have some ‘hierarchy of preference’ as far as available light sources goes, but it’s not entirely clear yet what it is. If both a bright moon and the Milky Way were both visible, it’s assumed that the beetles would focus on one.
There have actually been quite a few animals that have been proven to make use of the stars as a way to orient themselves and navigate the world. The dung beetle is, for now, the only animal shown to use the Milky Way for this purpose though.
Many species of birds have been found to make use of star light as a navigation tool (in addition to magnetoreception, smell, and vision), as well as certain species of insects. It’s very likely that there are other animals that make use of it too.
There has been some research in recent years suggesting that as light pollution from human settlements has been increasing many species have been losing their ability to navigate properly, especially during important times such as when some species gather for mating. Anyone who has ever witnessed a large swarm or gathering of insects around an artificial light source can attest to this.
Here’s some more information on the Milky Way, and observing it in the night’s sky:
“The Milky Way is the galaxy that contains our Solar System. This name derives from its appearance as a dim ‘milky’ glowing band arching across the night sky, in which the naked eye cannot distinguish individual stars. The term ‘Milky Way’ is a translation of the Classical Latin via lactea, from the Hellenistic Greek γαλαξίας κύκλος (pr. galaxías kýklos, ‘milky circle’). The Milky Way appears like a band because it is a disk-shaped structure being viewed from inside. The fact that this faint band of light is made up of stars was proven in 1610 when Galileo Galilei used his telescope to resolve it into individual stars. In the 1920s, observations by astronomer Edwin Hubble showed that the Milky Way is just one of many galaxies.”
“When observing the night sky, the term ‘Milky Way’ is limited to the hazy band of white light some 30 degrees wide arcing across the sky (although all of the stars that can be seen with the naked eye are part of the Milky Way Galaxy). The light in this band originates from un-resolved stars and other material that lie within the Galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, correspond to areas where light from distant stars is blocked by interstellar dust.”
“The Milky Way has a relatively low surface brightness. Its visibility can be greatly reduced by background light such as light pollution or stray light from the moon. It is readily visible when the limiting magnitude is +5.1 or better, while showing a great deal of detail at +6.1. This makes the Milky Way difficult to see from any brightly lit urban or suburban location but very prominent when viewed from a rural area when the moon is below the horizon.”
“The Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of the Earth’s orbit). Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth’s equatorial plane and the plane of the ecliptic relative to the Galactic plane. The north Galactic pole is situated at right ascension 12h 49m, declination +27.4° (B1950) near beta Comae Berenices, and the south Galactic pole is near alpha Sculptoris. Because of this high inclination, depending on the time of night and the year, the arc of Milky Way can appear relatively low or relatively high in the sky. For observers from about 65 degrees north to 65 degrees south on the Earth’s surface the Milky Way passes directly overhead twice a day.”