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A green ant game of thrones

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.

Green tree ants (Oecophylla smaragdina) are almost ubiquitous in tropical Australia. Image: Tuan Cao, Source: Wikipedia CC-BY-SA 3.0

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.

A green tree ant queen about to shed her wings and lay her first clutch of eggs. But where to lay them? Image: Wikipedia CC-BY-SA 3.0

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.

Thanks to ant ecologist Alan Andersen from Charles Darwin University for sharing this story.

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I have been observing these Queen Greens since 2013 at my rural home, Bees Creek (Darwin rural) and taking pics. 2013-2014, then none until 2017 and now again 2022, but on a guava tree rather than the usual 'cork tree' (carallia brachiata). They definitely produce silk to make their own group nests as there are no other Green Ants anywhere nearby. I can't tell you what happens after their larvae and pupae grow fully as I have never seen it reach that stage. In every case I have observed here, the Queens nests have been attacked by black ants, quite possibly after birds opened the nests as some opened nests had no Queens left in them. I'd like to send some pics/video but…

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