I shook off my arm the remainder of the insects who were aggressively intent on avenging the untimely death of their sister. I was in the Northern Territory, giddily soaking in myriad of natural history facts about Australia. These tasty ants, which feature prominently in the aboriginal cuisine, were definitely one of the highlights. Weaver ants are exceptional, even by the standards of a group of organisms that rival humans in the complexity of their social interactions and sophistication of their engineering. Only two species of the genus Oecophylla are known: in addition to the Australasian green weaver ants (O. smaragdina), the African weaver ant (O. longinoda) is found throughout most of sub-Saharan Africa. Both live in large arboreal colonies, and both exhibit an interesting behavior that has earned them the distinction of being silk weavers. When we think of silk, the first thing that comes to mind is of course underwear. The second is silkworms, and the ancient Chinese who first employed these insects to produce sophisticated garments. But weaver ants can also produce silk, yet, rather than spinning protective cocoons like moths, they use it in a way that is remarkably similar to the way we use crazy glue.
Being arboreal animals, weaver ants cannot build expansive underground galleries to protect their brood and queen. Instead, they pull together leaves and stitch them with sticky silk threads produced by their larvae – since adult workers do not have silk glands, some carry small larvae like tubes of glue, and squeeze them gently as they move back and forth between edges of two leaves. The leaves are temporarily held together by other members of the colony, often hundreds of them. The resulting arboreal nest is usually about the size of a football, and holds everything an ant colony needs – the queen’s chamber, a nursery for the larvae, and a larder full of prey. Weaver ants are voracious hunters – I have seen them attacking grasshoppers, beetles, snails, even snakes, and they are not opposed to partaking of carrion. I have also felt them attacking me, and this is one of the reasons why these ants are not popular among gardeners in Australia – having them rain on you from a tree and spray formic acid on your skin is not one of the most pleasant experiences. But at the same time weaver ants can be quite beneficial. It has been shown that their presence increases fruit production of some plants, and reduces the amount of pesticides needed to control pests. Unfortunately, like most ants, they have a weakness for sugar, and will protect aphids and scale insects that cause damage to plants. In the end, their impact on agriculture is probably about neutral. Some insects take advantage of the aggressive nature of weaver ants and, by assuming a similar appearance and hanging around their nests, gain protection from predators who dare not to get close to the ants. Katydids of the Australian genus Polichneare some of them, and it is still unclear how they manage to convince the ants not to eat them (chemical mimicry is the most likely explanation.) Since my initial encounter in Australia, weaver ants have been my favorite social insects, both off and on the plate. I have had them with rice and sweet cakes, and they always add to the experience. Sometimes ants on your picnic table are a good thing.