Dung Beetles Use the Milky Way for Orientation

Abstract

When the moon is absent from the night sky, stars remain as celestial visual cues. Nonetheless, only birds, seals, and humans are known to use stars for orientation. African ball-rolling dung beetles exploit the sun, the moon, and the celestial polarization pattern to move along straight paths, away from the intense competition at the dung pile. Even on clear moonless nights, many beetles still manage to orientate along straight paths. This led us to hypothesize that dung beetles exploit the starry sky for orientation, a feat that has, to our knowledge, never been demonstrated in an insect. Here, we show that dung beetles transport their dung balls along straight paths under a starlit sky but lose this ability under overcast conditions. In a planetarium, the beetles orientate equally well when rolling under a full starlit sky as when only the Milky Way is present. The use of this bidirectional celestial cue for orientation has been proposed for vertebrates, spiders, and insects, but never proven. This finding represents the first convincing demonstration for the use of the starry sky for orientation in insects and provides the first documented use of the Milky Way for orientation in the animal kingdom.

Diurnal dung beetles use the intensity gradient and the polarization pattern of the sky for orientation

“…Dung beetles use an impressive variety of celestial cues, including the sun (Byrne et al, 2003;Dacke et al, 2014), the moon (Dacke et al, 2004;Dacke et al, 2011), the solar and lunar polarization patterns (present study; Dacke et al, 2003a;Dacke et al, 2003b), the intensity gradient (present study) and even the Milky Way (Dacke et al, 2013b) for straight-line orientation. The flexibility offered by the ability to use more than one sky compass cue…”

“…To guarantee straight-line orientation, diurnal beetles are known to rely on a sun compass (Byrne et al, 2003;Dacke et al, 2014), and they seem to ignore available landmark cues (Dacke et al, 2013a). After sunset, crepuscular and nocturnal dung beetles use night-sky cues for orientation, such as the moon, polarized light formed around the moon (Dacke et al, 2003a;Dacke et al, 2003b) and light from the Milky Way (Dacke et al, 2013b). Whether diurnal dung beetles, like their nocturnal relatives, can orient to celestial cues other than the sun has, so far, not been tested.…”

Pulsar positioning system: a quest for evidence of extraterrestrial engineering

“…This may be achieved today with an experimental setup using the Goddard Xray Navigation Laboratory Testbed, also known as "the pulsar-on-a-table". A similar experiment has already been performed, using a planetarium to show that beetles can orient themselves thanks to stars (Dacke et al 2013).…”

Vision in dim light: highlights and challenges

“…The following two papers behaviourally dissect the specific visual cues that nocturnal dung beetles [4] and bull ants [7] use when navigating. Nocturnal dung beetles (figure 1b) have previously been shown to use the Milky Way for reliable orientation, and are well known to use this cue to maintain a straight-line course when rolling dung balls [3]. Foster et al [4] here used artificial celestial cues to quantify the constraints on the visual contrast that underlies this orientation behaviour-with just 13% contrast being sufficient at starlight levels.…”