Scarab beetle wheels
Another more unambiguous instance of wheel use in the organic world before the advent of humans can be found among scarab beetles. More precisely, this concerns those species that form dung balls and roll them around (Fig. 5). This rolling activity is one of the most amazing actions in the animal world and forms a combination of various techniques and a distinct art of craftsmanship and engineering. Most of this behaviour has been known since ancient Egyptian times and has been described by ancient authors such as Aristophanes, Plinius Secundus, Plutarch, and Horapollo (Levinson and Levinson, 2001).
More recently, beautiful and detailed descriptions have been provided by the French entomologist Jean Henry Fabre (reprint in translation, 1977). For detail I refer the reader to Fabre’s account and here I only wish to stress the parts related to the wheel aspect.
Dung beetles are attracted by the odour of fresh dung produced mainly by ungulates. They cut out pieces of dung and form a near-perfect bowl with a smooth surface by using their appendages and head structures. They then roll this bowl around to store it in excavated burrows as food for themselves or their offspring. By rolling the ball, they cover distances up to several meters while passing little elevations and valleys on their way. Mostly they push the rolling dung pills with a backwards walk, using their hind legs alternatively. The tips of the hindlegs form an axis that is parallel to the central axis around which the ball rotates. The combination of rotation around an axis, making use of the low friction resistance of circular and smooth surfaces to transport a heavy load, shows the closest degree of similarity to a wheel that I can think of. Interestingly, recent phylogenetic analyses of the dung beetles Scarabaeidae suggested that the dung rolling behaviour has evolved independently several times (Philips et al., 2004). Moreover, there is evidence that dung rolling was adaptively lost in several lineages of the Scarabaeini (Forgie et al., 2005). This provides an interesting parallel to the Middle East cultures in which the wheel was ‘forgotten’ and replaced by the use of domestic camels for several hundred years (see Bulliet, 1975).