“Tournaments and Slavery in a Desert Ant”, 1976-05-28 (; backlinks):
Many species of ants engage in physical fighting when territorial borders are challenged. In contrast, colonies of the honeypot ant species Myrmecocystus mimicus conduct ritualized tournaments, in which hundreds of ants perform highly stereotyped display fights.
Opposing colonies summon their worker forces to the tournament area by means of an alarm-recruitment system. When one colony is considerably stronger than the other, the tournament quickly ends, and the weaker colony is raided and its ants “enslaved”.
This is the first example of intraspecific slavery recorded in ants.
…However, in contrast to most ant species studied, the territorial conflicts do not consist of deadly physical fights, but, rather, of elaborate tournaments in which few ants are injured. Hundreds of ants participate in these affairs, which take place along the challenged territorial border. They can last for several days, being interrupted only at night when the species is normally inactive.
…I next investigated how the tournaments arise. When foragers venture into another territory, they frequently encounter foreign ants, whereupon they invariably begin to display on stilt legs. Subsequently some scouts return to their colony, dragging their abdominal tips over the ground. Upon arriving at the nest, they perform a conspicuous motor display in which they rush at nest-mates over short distances and perform rapid jerking movements. The locomotor behavior of members of the colony immediately increases. Within a few minutes, a group of 100–200 ants moves out and progresses rapidly in the direction from which the scouts approached the nest. Analysis of films reveals that these groups are regularly accompanied by the scouts, which still drag their abdominal tips over the ground. Upon encountering foreign conspecific workers at the disputed territorial area, the ants invariably perform the display behavior. Real physical fights, which occur rarely, usually end fatally for both opponents. During the course of the tournament, scouts of both colonies repeatedly return to their nests and recruit reinforcements to the battleground. However, if the defending colony is considerably weaker and therefore unable to recruit a large enough worker force to the tournament area, the colony will be overrun by the intruders and raided. Of 28 observed territorial invasions, 5 ended with the raiding of the weaker colony. During these raids the queens were killed or driven off. The larvae, pupae, callow workers, and honeypots were carried or dragged to the nest of the raiders. This process required several days and terminated only when the raided colony ceased to exist. Surprisingly, even during these raids, physical combats occurred only at the beginning and were infrequent. After several days the display behavior ceased, as the surviving workers of the raided colony were wholly incorporated into the raiders’ nest. Since, to my knowledge, all cases of slave-making in ants involve two different species, this is the first evidence for intraspecific slavery in ants.
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