Figure 1.

Antlion pits and spontaneous stratification. (a) An Euroleon nostras pit at the bottom of a hedge row in southwest Guernsey; coin diameter: 24 mm. (b) A cartoon of grain ejection and the segregation of ejected grains of two different sizes during pit construction: the larger (blue) grains are thrown on average further than the smaller (silver) grains in the same scoop of ejecta because their ratio of momentum to drag is higher. (c) A two-dimensional representation of the helical pit-construction trench; the irregular features are reversals of direction. (d) Close shot of an experimental ‘quasi-two-dimensional’, Hele-Shaw, cell as in [17]; a mixture of two grain types in equal volumes is poured from the top left corner and self-stratifies into successive layers of grains of each type [17]; the red rough sugar cubes are larger than the white round sand grains and have a greater angle of repose. (e) Simulated grains are poured as in a Hele-Shaw cell using the rules in our model; red: large grains; blue: small grains.