Green tree ants or weaver ants (Oecophylla smaragdina) are common, prominent and famous (or infamous) in northern Australia, from around Gladstone in Queensland to the Western Australia's Kimberley. There are only two species in the genus Oecophylla. Ours extends north from Australia into south-east Asia and to southern China, while another species occurs in tropical East Africa. Their near-ubiquity, abundant leaf-woven nests, aggressiveness, and irritating bites means that most people in the tropics are very familiar with green tree ants.
Despite this, we are in the dark about some crucial aspects of their lives.
All ant colonies begin with an inseminated female or queen who has mated during a nuptial flight. What happens next for most ants is straightforward. The new queen falls to the ground, sheds her wings, either digs a small burrow or finds a well-protected spot, lays her first batch of eggs, then tends the larvae. When these pupate they become the first generation of worker ants, who take on the foraging and colony maintenance roles, leaving the queen to lay more eggs (and more, and more...).
Green tree ants, though, have a problem, which is that they live in trees. A new queen can't easily make a nest. It takes many workers and a concerted effort to bend leaves together for nest-building, and adult ants (including the queens) can't produce the silk necessary to bind the leaves together. During nest-building by green tree ants, workers bring larvae from another nest and manipulate them to produce the necessary silk. A new queen can't do this.
So where does a mated green tree ant queen lay her eggs, and how does she protect the eggs, larvae and pupae during the crucial period of rearing her first batch of workers?
To solve this problem, mated green tree ant queens band together to form a mutual society. A bit like a bee swarm, the queens form a dense mass in a suitable tree. Each lays a batch of eggs, and tends them for several weeks until they pupate. The queens find safety in numbers - predators would be foolish to disturb a mass of highly aggressive, protective green ant queens.
And this is where the mystery lies. What happens next? A mature colony of green tree ants (which may comprise many nests spread over several adjacent canopies and with up to half a million workers) has only one queen. So how do green tree ants get from having dozens or hundreds of queens to one? Do the queens compete and only one survives? Do they disperse, and if so, how? Are the queens that band together closely related, in which case do some sacrifice themselves for the greater good? We simply don't know.
Dark biodiversity comes at many scales, from big mysteries (how did life evolve) to small ones. This is a small mystery. But it would be nice to know what happens during the green tree ant game of thrones.