Prey density and polyethism within hunting workers in the neotropical ponerine ant Ectatomma ruidum (Hymenoptera, Formicidae)

When supplied with numerous live prey, hunting workers of the Neotropical a nt Ectatomma ruidum can be subdivided into two categories: "stingers" speci alized in killing prey and "transporters" specialized in taking them one by one to the nest. We examined here how the division of labor between the hu nting workers is affected when different quantities of prey are supplied, a nd whether this response is associated with a perception of different total numbers of prey or different densities of prey, In seven colonies of diffe rent sizes, the increasing quantity of prey supplied was associated with an increase in the number of stingers from minimal to maximal values between which these two parameters were highly correlated. Moreover, there were sig nificant positive correlations between colony size and the minimal or maxim al value of the number of stingers, Whatever the colony size, when the numb er of stingers reached its maximal values, the proportion of workers in eac h behavioral subcaste of hunting workers was stable. Concurrently, a series of tests, where the number of prey, their density and the surface of the p redation site were alternatively maintained constant, indicated that each h unting worker estimated the "quantity of prey" according to their density a t the predation site, and not according to their total number.