With its abdomen poised in the air, a major worker readies to defend the nest.
Last week, Bug of the Week escaped winter’s chill to visit the beautiful Atala butterfly in southern Florida. This week we travel again, jumping hemispheres to sunny Queensland, Australia, to visit some remarkable members of the ant clan known as weaver ants. While bumbling through the underbrush in search of funnel spiders, I happened to bump into a small tree bearing several football-shaped clusters of glossy leaves. I was surprised and delighted when scores of beautiful green ants issued forth from one leaf-cluster and set to work defending their redoubt by dropping on my arm and attacking. Fortunately, the furious soldiers lacked stingers and their bite was mildly unpleasant at worst. The air was laced with the odor of formic acid released as a defense from specialized poison glands.
Unique nests
Green tree ants and other weaver ants represent a unique branch of the ant evolutionary tree. While other more familiar ants build colonies in soil or decaying wood, weaver ants live the life arboreal and construct clever nests in the canopies of trees. Nest building begins when one or more large workers, known as majors, grasp the margin of a leaf and fold it over or hold it in close proximity to an adjacent leaf. Other majors soon join the effort and in a fascinating display of cooperation they stand shoulder to shoulder to pull the leaf margins into close approximation to each other. When the gap narrows the workers stand in place, hold the leaf fast, and await the next step in the nest making process.
A single colony of green tree ants may consist of several smaller nests distributed in several trees.
Other workers gather almost fully developed ant larvae from deep within the colony. These youngsters are approaching their time of pupation, a time when they produce silk, and in their heads are fully functional silk glands. The workers gather several of these larvae and carry them to the construction site where leaf-grasping workers await their arrival. Using the silk-spinning larvae as living bobbins, workers move the larvae back and forth, weaving silk across the gap, and firmly stitching the leaves together. This process is repeated time and again with other nearby leaves until the nest is complete. Green tree ants build multiple nests throughout the tree’s canopy and several trees may be enlisted to house a single colony. In one of these individual nests resides the glorious queen, whose task it is to eat meals of protein and carbohydrates brought to her by the workers, and to lay thousands of eggs.
Early use as bio-control
Since workers large and small, young and old, share the same mother, the queen, they are all sisters and the building, care, and defense of the colony truly is a remarkable act of sisterly cooperation. The size of some weaver ant colonies has been estimated to exceed more than 500,000 workers. Like many of their kin, green tree ants are omnivores, consuming other insects they capture and gathering carbohydrates in the form of honeydew excreted by legions of arboreal sucking insects such as scale insects (see There's a sucker born every day - Tuliptree scale, Toumeyella liriodendri ). The value of weaver ants against pillaging plant-eating insects was recognized nearly 1,800 years ago by citrus growers in China. Ancient writings show that nests of weaver ants were regularly transported and installed in orchards where ravenous workers converted citrus-eating pests into food for the colony and queen – one of the first records of a practice still in use today called biological control.
Green tree ants are on high alert when nosy humans are nearby.
References
Bug of the Week thanks Dr. Shrewsbury for providing the photographs used in this episode. The spectacular reference “The Ants” by Bert Hölldobler and Edward O. Wilson provided the information used in preparation of this episode.
To learn more about green tree ants and other weaver ants, please visit the following web sites:
http://ngm.nationalgeographic.com/2011/05/weaver-ants/chadwick-text
http://www.soe-townsville.org/greentreeants/index.html