Photo by Lepidlizard
Green tree ants are about 5 mm long and yellowish-green. They are common all across northern Australia.
Green tree ants unlike other ants live and build nests in trees. Green ant nests are made of leaves pulled together and woven with silk produced by their larvae. The nests can be as big as a football.
Photo by Michael Gorey
They are found on all types of trees. They are very aggressive and defend their nests by swarming onto the intruder. The green tree ants grab onto your skin with their legs and bite a hole. They then pull their tail underneath themselves and squirt acid into the wound.
I know from personal experience these ants are everywhere and it is painful (but not lasting) when you are attacked. You definitely do not want to disturb a nest.
Junior Ranger Nature Notes, Green Ants
Green Tree Ant, Queensland Museum