My first proper article of the new blog just had to be about ants. Despite being ecologically vital parts of the natural world, ants are widely misunderstood – even hated – by some people. Hopefully this will set the record straight.
They march along the dense tangle of vines and branches of tropical jungle, across the undergrowth of the world’s boreal forests, over the scorching crests of sand dunes, and even on the hot tarmac of our city streets. Ants are to be found almost everywhere we care to look.
When it comes to diversity, however, ants are not especially impressive compared to other insect groups. Approximately 13,500 species are currently described, with somewhere between 25,000 to 30,000 species estimated to exist (AntCat, 2019). This is about 1% of known insect species!
No, the importance of ants comes from their sheer abundance. Very roughly, there are an estimated 10,000 trillion individual ants alive at any one time, weighing around the same as all human beings combined (Hölldobler and Wilson, 1994; Lach et al., 2010). To support such a high biomass, by definition, ants will exert important effects on the organisms around them. For example, ants are the primary predators of invertebrates in lowland tropical rainforest (Floren et al., 2002), important decomposers and conduits of energy in most measured terrestrial environments, and leaf-cutter ants are key herbivores in Neotropical forests (Wirth et al., 2013). But their roles within ecological communities – biocoenoses, if you will – can be more diverse. Ants are also key seed dispersers, soil turners, and nutrient movers. Plants growing near ant nests enjoy increased nutrient concentrations in the surrounding soil, e.g. the host plants of Azteca ants have >800% of nitrogen, phosphorus, and potassium in the soil surrounding their roots compared to leaf-litter, affording greater growth rates (Lucas et al., 2018).
Ants have also formed some of the most interesting and important mutualisms and associations with other organisms. Most species of ant, though 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