Digging the optimum pit: antlions, spirals and spontaneous stratification

Nigel R. Franks, Alan Worley, Max Falkenberg, Ana B. Sendova-Franks, Kim Christensen

Research output: Contribution to journalArticle (Academic Journal)

4 Citations (Scopus)
12 Downloads (Pure)


Most animal traps are constructed from self-secreted silk, so antlions are rare among trap builders because they use only materials found in the environment. We show how antlions exploit the properties of the substrate to produce very effective structures in the minimum amount of time. Our modelling demonstrates how antlions: (i) exploit self-stratification in granular media differentially to expose deleterious large grains at the bottom of the construction trench where they can be ejected preferentially, and (ii) minimize completion time by spiral rather than central digging. Both phenomena are confirmed by our experiments. Spiral digging saves time because it enables the antlion to eject material initially from the periphery of the pit where it is less likely to topple back into the centre. As a result, antlions can produce their pits-lined almost exclusively with small slippery grains to maximize powerful avalanches and hence prey capture-much more quickly than if they simply dig at the pit's centre. Our demonstration, for the first time to our knowledge, of an animal using self-stratification in granular media exemplifies the sophistication of extended phenotypes even if they are only formed from material found in the animal's environment.

Original languageEnglish
Article number20190365
Number of pages9
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1899
Early online date27 Mar 2019
Publication statusPublished - Mar 2019


  • animal traps
  • extended phenotype
  • granular materials
  • optimized construction
  • self-organization
  • spontaneous stratification

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    Franks, N. R., Worley, A., Falkenberg, M., Sendova-Franks, A. B., & Christensen, K. (2019). Digging the optimum pit: antlions, spirals and spontaneous stratification. Proceedings of the Royal Society B: Biological Sciences, 286(1899), [20190365]. https://doi.org/10.1098/rspb.2019.0365