Complex fluids in the animal kingdom

Abstract

Animals have evolved distinctive survival strategies in response to constant selective pressure. To demonstrate the importance of complex fluids and flow phenomena in the animal kingdom, species that utilize complex fluids as part of their survival strategy are introduced and discussed. In detail, we review how animals cope with and use exogen or endogen, biotic or abiotic complex fluids as a competitive advantage for movement, prey, defense, and reproduction. We demonstrate how animals learned to manipulate their habitat, e.g., sandfish and crabs that exploit the granular rheology of sand (exogen abiotic) and showcase exotic animals that produce unique bio-fluids (endogen biotic), from deep-sea hagfishes to subterranean velvet worms. For unknown and uncharted phenomena, potential rheological properties of the involved complex fluids are suggested. This contribution aims to assess complex flow behaviors used by animals in nature, compare and reveal the effect of material properties on biological behavior, and demonstrate the importance of rheology in nature.