Ritualised fighting in Iridomyrmex purpureus
The meat ant species Iridomyrmex purpureus is one the most abundant and obvious ants across much of southern Australia. They form large pebble-covered nests, with colonies consisting of numerous individual nests, these nests often connected by well-worn "highways". Colonies normally consist of about 7 individual nests but this can vary from only a single nest up to over a dozen nests, with a single queen per colony. Nests are generally placed near food sources, minimising foraging times and making the colony more efficient, and colonies will abandon nests as food sources shift location.
A well-worn highway connects two nests within a colony of I. purpureus.
It is well known that these ants are highly territorial with well defined boundaries being established between colonies. These boundaries are not physical but are maintained by workers of neighboring colonies through highly stereotyped ritualised fighting, these confrontations sometimes lasting months and repeated over a number of years. These interactions are rarely fatal with the occasional minor injury being the most serious consequence for individual ants. While the vast majority of interactions between meat ant colonies are ritualised (some 95%), a few involve lethal fighting. This lethal fighting seems to occur in situations where a foreign ant has invaded the territory of another colony and the fighting is initiated by the resident ant defending its colony. Thus these ants normally undertake ritualised fighting to establish and maintain colony boundaries with minimal injury to the colonies, but they will escalate to lethal fighting if their colony is under direct threat.
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