Figure 1.

Solenopsis invicta workers digging tunnels. (a) Comparison of size difference between small and large workers. (b) Ventral view of a tunnelling worker. (c–e) The mechanics of tunnel excavation involve loosening, carrying and transporting substrate (0.25 ± 0.04 mm diameter wetted glass particles) from the tunnel face to the surface (see electronic supplementary material for videos). Excavated material is loosened and manipulated using the mandibles. (f) Excavated material is held in the mandibles and carried to the surface (direction designated by black arrow). (Online version in colour.)