Researchers for a new study of insects found that individual ants are of little value to the colony of a species of ant from Sub-Sahara Africa. Ant’s after all have a massive population and losing an individual insect is rarely missed by the colony. But they found that it does pay off for the colony as a whole, to invest in the rescue of lightly wounded and injured ants from a raid against furious termites. The termite soldiers are no pushover, they ferociously fight against the raiders by biting the limbs off the invading ants.
The study found that social wound treatment in these insects goes through a multifaceted triage health care system focused entirely on the injured individuals. This mechanism of wound treatment is not only limited to the rescue of lightly injured individuals, but also includes the treatment inside the nest. This triage system reduces mortality of the rescued invaders by 90%.
The injured ant decides for herself whether to be treated and rescued during the raid, by unconsciously determining the severity of it’s injury. It than alerts the raiding party that medical attention is needed. The more severe the injury, the more likely the rescuer will receive a message from the injured by not cooperating in their own rescue. Those wounded ants are left behind.
Matabele ants returning from a successful raid. The big ant carries two termite soldiers of Macrotermes sp. in its mouth as prey.Amina Khan of the Los Angeles Times writes:
Move over, ant farms—ant hospitals are where the real action is. Scientists studying the behavior of African Matabele ants in Ivory Coast have found that the insects act like paramedics in a crisis, triaging and treating the wounds of their injured peers.
The discovery, described in the Proceedings of the Royal Society B, documents a surprisingly sophisticated system that helps determine which ants are most likely to survive a combat injury.
Ants are often thought to live in systems where the life or death of an individual worker doesn't matter much. That's because many ant species live in giant colonies whose workers usually have very short life spans relative to the queen, and because the queen can lay eggs for new workers at a fast rate.
"The benefit from helping injured ants in this scenario is small, because replacing them should be easier," the scientists wrote. "At the same time, if injuries were mainly fatal, the benefit of a rescue behavior focused on injured individuals would again be marginal."
A Matabele ant treats the wounds of a nest mate whose limbs were bitten off during a fight with termite soldiers.From the Proceedings of the Royal Society B (Biology).
Open wounds are a major mortality risk in animals [1] and likely to get infected without treatment. We therefore expect species that are prone to losing extremities to develop means to reduce the mortality risks these injuries pose. Social predatory species that hunt prey capable of inflicting injuries fit this criterion. Ants are generally assumed to have large colonies in which the individual worker hardly counts (i.e. a very large population turnover: large colony size and high birth rate) [2]. The benefit from helping injured ants in this scenario is small, because replacing them should be easier [3]. At the same time, if injuries were mainly fatal, the benefit of a rescue behaviour focused on injured individuals would again be marginal [3]. The ponerine group-hunting termite specialist Megaponera analis fits all the criteria where a rescue behaviour focused on injured ants has a large benefit for the colony [3].
Megaponera analis is found in sub-Saharan Africa [4] and specializes in hunting termites solely from the subfamily Macrotermitinae [5–7]. These ants leave in groups of 200– 600 individuals to termite foraging sites, which can be up to 50 m away, in a column formation led by a scout that previously investigated the foraging site [5,8–10]. At the hunting ground, division of labour occurs: while the majors break open the soil layer covering the termites, the minors rush into these openings to kill and carry out the prey [11–13]. The hunting process lasts 5–10 min after which the termites get collected in the mandibles of the majors and the group returns together back to the nest in the same column formation [10,13]. During the hunt, some ants get injured by termite soldiers, which have strongly sclerotized heads and mandibles [14]. These ants often lose limbs or have termites clinging to them [3,5,15]. Before returning to the nest, nest-mates search for these handicapped ants, which call for help with pheromones in the mandibular gland, consisting of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) [3]. After a short investigation, a nest-mate picks up the injured ant and carries her back to the nest within the safety of the returning group. However, ants that are fatally injured are left behind [3]. If the injured ants were to return alone to the nest, they would die in 32% of the cases during the return journey [3]. Within the nest, the termite soldiers get removed by nest-mates, thus fully rehabilitating the handicapped ant. Ants that lost extremities are capable of changing their locomotion to a four- or five-legged gait in less than 24 h and are capable of reaching running speeds similar to healthy ants again [3]. These injuries occur regularly, with roughly a third of the minors participating in raids having lost a leg at one point in their life [3]. Saving the injured, therefore, significantly increases the fitness of the colony [3]. While the benefit of being carried back to the nest is clear (reduced predation risk), it is still unclear what risk open wounds (cut limbs) pose for the injured individual and the colony.
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