Blatant thievery among colonies of tiny tropical ants may allow them to prosper in part because the species is more peaceful than the vast majority of its closely related relatives, according to a University of Colorado at Boulder study.
The odd practice of food theft among neighboring colonies of the ant species Ectatomma ruidum is fostered by "chemical camouflage" used by larcenous ants to enter nearby nests, said CU-Boulder biology Professor Michael Breed. Success also depends on the vigilance of guard ants posted at nest entrances to eject intruders.
Chemicals are the primary comunication tools of ants and bees, Breed said. Each member of an ant or bee colony appears to carry a distinct aroma from a colony-specific hydrocarbon compound on their bodies -- an evolutionary strategy that alerts colony members to interlopers trying to gain entry to their nest.
Unlike most ant and bee guards, which kill would-be intruders, E. ruidum guards simply wrestle intruders away from the nest entrance and set them down. But the skirmishes -- similar to bar bouncers ejecting unruly patrons -- ironically transfer the correct chemical password for nest entrance from the bodies of the guards to those of the interlopers, ensuring successful nest entry by intruders on their next attempt.
"If the guard ants killed the intruders, this system of larceny would come to a crashing halt," Breed said. "It may be that this species is physically incapable of killing individual members, or it may just be a kinder, gentler ant species."
E. ruidum ants generally live in small, shallow nests in the ground, each hosting from up to 200 ants and a queen ant. But Breed is doubtful that the thieving ants -- found from Central America to the Amazon -- are aware of their deceptive behavior. "I don't think we can give these ants credit for being cognitive," he said.
In a field study by Breed and three CU-Boulder students in fall 1998, a
number of different E. ruidum co
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Contact: Michael Breed
Michael.Breed@colorado.edu
303-492-7687
University of Colorado at Boulder
15-Mar-1999