Two Neotropical ant species, Stenamma expolitum Smith and S. alas Longino, exhibit three unusual nesting behaviors: (1) they build architecturally sophisticated nest entrances that elevate the nest opening away from the surface; (2) they maintain multiple identical nests but occupy only one of them; and (3) they keep a round "door pebble" at the nest entrance, with which they plug the opening in response to army ants. Adaptive hypotheses for these behaviors are discussed, including the possibility that they are multiple lines of defense against army ant predation.