page_title: Rotating locomotion in living systems
section_title: Rolling
hierarchical_section_title: Rotating locomotion in living systems / Known instances of rotation in biology / Rolling
caption_attribution_description: Deutsch: Eingerolltes Steppenschuppentier (Manis temminckii), Madikwe Game Reserve, Südafrika
context_page_description: Several organisms are capable of rolling locomotion. However, true wheels and propellers—despite their utility in human vehicles—do not appear to play a significant role in the movement of living things. Biologists have expounded on the reasons for this apparent absence of biological wheels, and wheeled creatures have appeared often in speculative fiction.
  Given the ubiquity of the wheel in human technology, and the existence of biological analogues of many other technologies, the lack of wheels in the natural world would seem to demand explanation—and the phenomenon is broadly explained by two main factors. First, there are several developmental and evolutionary obstacles to the advent of a wheel by natural selection, addressing the question "Why can't life evolve wheels?" Secondly, wheels are often at a competitive disadvantage when compared with other means of propulsion in natural environments, addressing the question "If wheels could evolve, why might they be rare nonetheless?" This environment-specific disadvantage also explains why at least one historical civilization abandoned the wheel as a mode of transport.
context_section_description: Some organisms use rolling as a means of locomotion. These examples do not constitute the use of a wheel, as the organism rotates as a whole, rather than employing separate parts which rotate independently.
  Several species of elongate organisms form their bodies into a loop to roll, including certain caterpillars (which do so to escape danger), tiger beetle larvae, myriapods, mantis shrimp, Armadillidiidae, and Mount Lyell salamanders. Other species adopt more spherical postures, primarily to protect their bodies from predators; this posture has been seen in pangolins, wheel spiders, hedgehogs, armadillos, Armadillo girdled lizards, isopods, and fossilized trilobites. Pangolins and wheel spiders have been observed to purposely roll away from predators. These species may roll passively (under the influence of gravity or wind) or actively, typically by altering their shape to generate a propulsive force.
  Tumbleweeds, which are the above-ground portions of certain plants, separate from their root structure and roll in the wind to distribute their seeds. These plants are found especially in open plain environments. The most well-known of these include Kali tragus (also known as Salsola tragus), or prickly Russian thistle, which arrived in North America in the late 19th century, and gained a reputation as a noxious weed. Fungi of the genus Bovista are known to use the same strategy to disperse their spores.
  Rotifers are a phylum of microscopic but multi-celled animals, typically found in freshwater environments. Although the Latin name rotifer means 'wheel-bearer', these organisms do not have any rotating structures, but rather a ring of rhythmically beating cilia used for feeding and propulsion.
  Keratinocytes, a type of skin cell, migrate with a rolling motion during the process of wound healing. These cells serve to form a barrier against pathogens and moisture loss through wounded tissue.
  Dung beetles form spherical balls of animal excrement, which they roll with their bodies, generally by walking backwards and pushing the ball with their rear legs. Phylogenetic analysis indicates that this rolling behavior evolved independently several times. The behavior of these beetles was noted in ancient Egyptian culture, which imparted sacred significance to their activities. Although it is the dung ball that rolls rather than the beetle itself, the beetles face many of the same mechanical difficulties that rolling organisms contend with.
caption: The pangolin Manis temminckii in a defensive posture, in which it can roll
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