Oecophylla smaragdina: 10 Facts About Weaver Ants and Green Tree Ants

3 days ago

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Oecophylla smaragdina is one of the most famous ants in the world. It lives in trees, builds its nests by sewing living leaves together and defends its territory against anything that moves. In Asia it is known as the weaver ant, in Australia as the green tree ant. Here are ten facts about this remarkable species, and the differences between the Asian and Australian forms.

1. Its name means emerald leaf-house

Oecophylla comes from the Greek for leaf-house, which describes its nests perfectly. Smaragdina means emerald, after the greenish colour of the queens.

Greenish Oecophylla smaragdina queen on a leaf with eggs — A weaver ant queen with eggs. Smaragdina means emerald.

2. It sews with its own larvae

Adult weaver ants cannot make silk. Their larvae can. To close a nest, workers carry a larva in their jaws and move it back and forth between two leaves like a living glue stick, while the larva spins silk threads that stitch the leaves together. The building usually happens at night.

Weaver ant leaf nest hanging in a tree — A leaf nest, stitched together with larval silk.

3. Teamwork that defies the rules

To pull two leaves together, workers form living chains, holding on to each other by the waist. Normally each member of a group works a little less hard as the group grows. In weaver ants it is the other way around: in these chains each ant pulls about twice as hard as it would on its own, because the ants holding on store the force of the ants pulling.

Green tree ant workers working together on a leaf at night — Workers at work on a leaf.

4. One colony, many trees

A mature colony can grow to around half a million ants. One colony was found living in 151 nests spread over 12 trees. The queen sits in one of those nests, and her eggs and young are carried to the others. A mature colony can last around eight years.

5. Two kinds of workers

The smaller minor workers, roughly 5 to 7 mm, mostly stay home to care for the brood and tend scale insects for their sweet honeydew. The bigger majors, roughly 8 to 10 mm, with long legs and big jaws, forage, build and defend. The queen is much bigger, roughly 20 to 25 mm.

Orange weaver ant workers tending scale insects on a branch — Workers tending scale insects for their honeydew.

6. No sting, but a nasty bite

Weaver ants do not have a sting. Instead they bite and then spray an irritating fluid from their gaster into the wound. They use two different scent signals: one to lay trails that bring in large numbers of nestmates, and one to rally workers close by when an intruder appears.

Orange weaver ant worker in a defensive pose with its gaster raised — Ready to bite and spray.

7. The oldest pest control in the world

Farmers in China used weaver ants to protect citrus orchards against pests as early as 304 AD. That is the oldest written record of biological pest control. Today they are still used in orchards with mango, cashew, cocoa, coconut and coffee. In Sri Lanka, coffee growers once gave it up because picking the beans between the biting ants was too painful.

8. A snack with a lemon flavour

In Thailand and the Philippines the larvae and pupae are eaten and are said to taste creamy and sour, like lemon. On Java they are harvested and sold as kroto, food for songbirds and fishing bait. In Australia, First Nations peoples eat the green gaster of the workers, which tastes strongly of lemon, and crush the ants with water to make a drink for colds and sore throats.

9. Friends and enemies

Some Australian oak-blue butterflies only live where weaver ants live, because their caterpillars depend on the ants. A jumping spider, Cosmophasis bitaeniata, copies the smell of the ants to sneak into the nest and eat the larvae, while another jumping spider copies their shape. And a newly discovered Australian spider even catapults green tree ants into its web.

10. Two forms: Asia and Australia

Oecophylla smaragdina spread from mainland Asia via the Indonesian islands, Sulawesi and New Guinea all the way to northern Australia. DNA research shows that the Asian and Australian populations are genetically different, and Australia was probably colonised twice. You can also see the difference:

Asia: workers are mostly orange to reddish brown. This is the classic weaver ant.
Australia: many workers have a bright green gaster, hence the name green tree ant. Green and more yellowish forms live side by side.
Queens: colonies around Darwin in the Northern Territory regularly have several queens, while colonies in Queensland and on Java usually have just one.

Orange Asian weaver ant worker next to scale insects on a branch — The Asian form, with bright orange workers.

Australian green tree ant worker with a green gaster on a leaf — The Australian form, with a green gaster.

Keeping weaver ants yourself

Weaver ants are one of the most spectacular species you can keep, but they need a tree-like setup, warmth, humidity and very good escape prevention. Everything about care is in our Oecophylla smaragdina care guide. Have a look at our Asian Oecophylla smaragdina colonies and our Australian Oecophylla smaragdina colonies, or read more surprising behaviour in our 10 bizarre ant facts.

Sources

Wikipedia. Oecophylla smaragdina.
Schlüns, E. A., Wegener, B. J., Schlüns, H., Azuma, N., Robson, S. K. A. and Crozier, R. H., 2009. Breeding system, colony and population structure in the weaver ant Oecophylla smaragdina. Molecular Ecology.
CORDIS, European Commission. ANT BIODIVERSITY project.
Warndu. Green ants, the future of food.