About 3 mm long
These ants are harvester ants in that they collect seeds but they also scavenge. Their name comes from the flat shield on their thorax, fringed with protective spines. They have the ability to curl up when threatened, folding their antennae away in the grooves on the sides of their heads, so that an attacker is confronted with spines or hard surfaces wherever they are approached. Figured is a specimen seen in Victoria, photo courtesy of Alex Wild, http://www.myrmecos.net/ants/. The grass remains around the nest photo are from Bothriochloa pertusa, Indian bluegrass.