ough to varying degrees, tap into the rich sugary reserves made available by aphids, scale-insects, and other exudate-producing insects – otherwise known as “honeydew”. This source of carbohydrate is vital for worker ants to remain highly active and is especially important in species that form larger colonies. Thus, the quest of the ants is to protect their honeydew-producing comrades from parasites and predators. Indeed, when these mutualists are found alongside ants, they can reach much greater numbers than those without their armoured myrmidons. In a sense, ants act as important herbivores via these mutualists.
Army ants, however, are simply next-level when it comes to mutualisms with other organisms. There are 557 recorded species associated with the army ant Eciton burchellii, which can form marauding colonies 700,000 individuals strong (so called ‘bivouacs’). These ants roam the tropical forests of South and Central America, predating upon anything they can catch and overpower, including mammals, amphibians, and birds in their nests. Many of the mutualists of army ants, and ants more generally, tend to be small arthropods (e.g. mites, beetles, bugs) that live within the bivouac and feed on the waste of the colony. Others are parasites of the colony that may follow the swarm and predate upon the ants themselves. Antbirds, creatively named, are famed for their association with army ants. These birds hop along behind the raiding front, picking up invertebrates flushed out by the ants. This is a form of parasitism called ‘kleptoparasitism’ (essentially theft). The ants have learned that large-bodied prey items need to be brought beneath the leaf-litter before butchering to prevent the antbirds from stealing them! Around twenty species of antbirds are obligately associated with army ants and many more facultatively. Ergo, army ants are at the centre of a tight-knit biocoenosis. What a shameless self-plug.
If their impressive ecological dominance or diverse associations aren’t enough for you, perhaps their unique life-histories will convert you to myrmecophily (myrmex- ant, phílos- love). The fact that ant workers readily sacrifice themselves for what seemed to be ‘the greater good’ of the colony posed a serious problem to Darwin when he was formulating the theory of natural selection (1859).
How could evolution have favoured a strategy where individuals only very rarely reproduce themselves? In essence, viewing ants and other animal societies, and especially social insects, as ‘superorganisms’ has gone a long way to answer Darwin’s vexation. These superorganisms are comprised of individuals that are usually very closely related, and thus promote the inheritance of their genes indirectly (a theory called ‘kin selection’) by helping their relatives reproduce i.e. the queens and drones. Natural selection then works primarily not at the level of the individual, but at the level of the colony, and thus workers optimize the running of the colony to increase the success of their own genes via the reproductive members of the group (Lach et al., 2010). This also only works in an evolutionary sense because colonies are so much better at completing tasks than individuals. By using “series-parallel” operations, workers switch from one task to another when it’s efficient to do so, meaning that each task is completed more quickly and efficiently than if it was completed by the same number of uncoordinated individuals. This reasoning also scales up – larger colonies are more efficient at completing tasks than smaller colonies (Hölldobler and Wilson, 1990; 2009). Isn’t that an interesting metaphor for human societies?
I’m not done. Ever wonder why all ant workers are female? WELL! You’re in for a treat. Animals have a whole range of different methods to differentiate the sexes of offspring during development. Humans have the X-Y determination system; females have two X sex-chromosomes and males have one X and one Y sex-chromosome. Simple. Ants, on the other hand, have a system called ‘haplodiploidy’ where females arise from being diplo