“Territoriality in the Malaysian Giant Ant Camponotus Gigas (Hymenoptera/Formicidae)”, 2001-12 ():
[ritualized combat ‘tournaments’] In a 5-ha [hectare: 10,000 m2/2.47 acres] area of primary lowland rain forest in Borneo, we observed 4 polydomous colonies of the night-active giant ant Camponotus gigas. The non-overlapping, 3-dimensional territories in the canopy had a ground size up to 0.8 ha. C. gigas showed a distinct territorial behavior: (1) specific “barrack” nests, especially containing many majors, were situated at the borders and were established during long-term territorial conflicts; (2) trunk trails were regularly patrolled by majors that attacked alien conspecifics and some other ant species violently; and (3) sentinels, often involved in long-enduring conflicts with neighboring ant colonies, defended the borders at bridgeheads.
Interspecific conflicts with sympatric Camponotus species always led to violent, “bloody” fights of all castes. Intraspecific conflicts, however, were solved by ritual fights (“front leg boxing”) of majors. C. gigas performed a de-escalation strategy to end short periods of true intraspecific “ant war” that we provoked experimentally.
Artificially induced ritualized combats continued over weeks also in the absence of baits, indicating that borders may become established by long-term conflicts of attrition. We discuss the differences between ritual fights in desert and rain-forest ants and apply Lanchester’s theory of battles to our findings.
…Results of the fighting experiments: starting an “ant war”: We provoked 3 long-term conflicts between adjacent colonies to obtain more information about the conflict strategies of C. gigas.
…As the trail was only 2cm wide, a fighting major could block it. Hostile majors fought each other ritually; they “boxed” with their front legs and pulled each other at the mandibles (for details, see following). If the attacking ant won, it could pass and went on further to the enemy nest. Defenders that were already fighting had to let other majors pass also. Most of the minors retreated to their nest…At our second experiment, which took place 1 week later at the same place, fighting did not escalate as before: both colonies recruited fewer than 10 majors that each fought only in a ritual manner, and minors withdrew completely from the tournament place. This time we did not break down the connecting trail in the morning, so both colonies kept in contact. Ritual fighting continued over 30 days and guards were observed for at least 45 days. As the earlier individual markings showed, these were the same individuals during the whole time.
…Ritual combat: We observed ritual tournaments during territorial conflicts at 8 colonies of Camponotus gigas and took quantified data (n = 180 fights) from 4 colonies. Generally, ritual tournaments were restricted to majors that fought each other only in a ritual manner. Figure 4 illustrates all possible (partly overlapping) phases of the behavioral repertoire that arose during a confrontation between two major ants of antagonistic colonies.
The fighting occurred as follows: the assailant went to the border of the opposing colony, where the alien major was standing sentry. Occasionally the aggressor drummed at the ground with its gaster, producing audible sound. It opened its mandibles and reared the first pair of legs. When it touched the defender, the fight began…Each major tried to grasp its antagonist at its mandibles. Then, with a quick jerk, the inferior ant was deprived of its balance and was pulled over the ground in a retrograde movement. After a short distance, the ant was released and both parties retreated. Mostly, the decision was made while “boxing”. The “round” was won by the ant that was able to hold up its front legs longer; its opponent retreated immediately.
Such a victory did not stop the combat. It was only interrupted by a short period of self-grooming of antennae and front legs. In these breaks, ants often retreated to their territories, where 2–3 of their major nest-mates were still on guard. Sometimes (n = 18⁄180) the fighters started boxing again when they met their nest-mates, but they did it in a weakened form. The sequence of the movements was much slower in comparison to real fights. The mandibles were opened only half way, and the tarsi were not raised as high and never touched the nestmate…Mostly, just one or two pairs of majors were fighting, while the other majors were involved in the combat only rarely. We rarely observed two or 3 majors attacking one opponent on the ground, but, if so, this never happened other than in a ritual way…In only 2⁄180 fights that we observed did aggression become so intense that neither fighter released their mandible grip; instead, they sprayed acid on each other and died within minutes.
…Resources used by C. gigas are randomly distributed: invertebrates, bird droppings, and cadavers, on which C. gigas feeds occasionally, are widely dispersed within the rain forest, as well as groups of trophobiotic Homoptera (1997). Territories of C. gigas colonies had clear-cut borders that were defended even in absence of a bait against intra-specific & interspecific enemies. However, this defense was restricted to the arboreal parts of the territory and took place at “bottlenecks” that gave the opportunity to guard them with a few majors, eg. the base of the trees. On the ground, C. gigas guarded only the immediate surrounding of their nest entrances, and resources were used in scramble competition. Similar findings were reported by 1984 from Cameroon, who found exclusive territories only in tree-dwelling ant species; ground-dwelling ants had overlapping territories because of the lack of “bridgeheads” that could be easily protected. Partly, this finding may also reflect problems with territorial marking, which is much easier on arboreal trails than on large ground areas. Our data show that in C. gigas territorial marking supported the dominance of territory owners.
…C. gigas showed two different strategies to defend its territory: (1) ritual combat during intraspecific competition and (2) “true”, violent fights in interaction with other ant species. Ritualization seems to have evolved in many ant species because the lack of a fixed territory can lead to frequent confrontations of workers from neighboring colonies. These species have overlapping territories, foragers of different colonies that meet in the field perform short displays of ritual aggression behavior
[see 1976] …In the tournaments of M. mimicus, Lumsden & 1983 distinguished between two models that would allow the opposing colonies to assess each other’s strength: ‘head counting’ and ‘cast-polling’ (1984). Head counting could be measured most easily in the arboreal fights of C. gigas, as fighting majors formed pairs along the trails during combat. Additional majors could pass these fighters and reach the nest of their opponents, thus taking advantage of their local majority. Cast-polling was also easy: smaller majors had less strength and were tired within a shorter time; they had to be replaced more frequently. As most of the combats were carried out by only a few majors (especially when the “hot phase” was over), it seems that cast-polling was enough to determine the strength of a colony. This hypothesis is supported by the fact that minors had a strong tendency to withdraw from prolonged agonistic encounters. One strong ant could stop a number of opponents when it blocked the narrow arboreal trails. It is likely that, for energetic reasons, the strongest majors could be produced by large colonies only. All combats that we observed were solved by a strategy of de-escalation.
…Not only was the method of the combat ritualized, in the end the fight itself involved representatives, possibly because its arboreal territory could be protected most effectively by a few strong majors. In the rain forest, it seems to be more appropriate to guard certain bridgeheads of a fixed territory over a long time, whereas in a desert environment a ritual fighting strategy needs more participants.