Dear Editor:rnExcept during few events in their life cycles,such as nuptial swarm and mass migration,red imported fire ants,Solenopsis invicta Buren,avoid being exposed to the open air by living in a unique nest system.The nest provides the colony with a controlled environment and an abundance of foraging tunnels,critical for the survival of an ant colony by reducing the risk of desiccation and predation.As a fundamental behavior in both nest and foraging tunnel construction,digging behavior is precisely regulated.For example,the volume of a fire ant mound is proportional to the colony total weight(Tschinkel,1993).In other words,ants can assess the volume of their nests.When a nest reaches a critical volume,ants will slow down or stop their digging behavior.Although unquestionably important,the mechanism of digging behavior regulation in red imported fire ants has not been intensively studied.