weaver ant
What are the two species of weaver ants and where are they found?
How do weaver ants construct their nests?
What are the main foods of weaver ants?
How are weaver ants used in sustainable agriculture?
weaver ant, (genus Oecophylla), genus of two species of arboreal ants easily recognized by their intricate nests of woven leaves and hailed as one of the pinnacles of ant social evolution. The African weaver ant (Oecophylla longinoda) is found in tropical forested areas of Africa, and the range of the Asian weaver ant (O. smaragdina) includes southeastern Asia, northern Australia, Papua New Guinea, and the Solomon Islands. Weaver ants are used as a biological control agent against insects that damage tropical tree crops, and the ants and their larvae are a popular food in parts of Southeast Asia. The ants are among the most abundant and dominant social insects of the Old World tropics.
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Formicidae
- Tribe: Oecophyllini
See also list of ants, bees, and wasps.
Nest construction
Unlike most terrestrial ants, weaver ants do not nest underground but rather build their nests in trees, using living leaves growing near the ends of the branches. They prefer broad-leaved trees, such as mango and ylang-ylang, and they often inhabit the edges of forest clearings or trees along the banks of rivers that are less shaded.
Working together, weaver ants grab the edges of a leaf in their mandibles and curl the leaf toward itself. Once the leaf is in position, other workers carry nearly mature larval weaver ants to the leaf edges and tap the heads of the larvae gently, causing the larvae to expel strands of strong silk from a gland under the mouth. Each larva is then passed back and forth as a living shuttle to glue the edges of the leaf or multiple leaves together. Thousands of strands of larval silk are woven into sheets between the leaf edges of the nest, creating a living waterproof shelter.
A new queen will initially construct a nest of a single leaf. The nest is expanded as the colony grows, sometimes reaching the size of a basketball or beach ball. Unlike other arboreal ants, whose colonies nest in existing cavities or in other confined spaces and are thus size-constrained, weaver ant colonies can reach incredible sizes. Some colonies comprise hundreds of thousands of ants and require additional nests, which are positioned as satellites along the edges of the colony’s territory to guard against invaders. Such networks can give a colony control of several trees at a time. The oldest major workers in the colony often live in these outpost nests, because they are considered to be more expendable than younger ants.
Natural history
As in those of other ant species, each weaver ant colony has three castes: fertile queens, infertile female workers, and male drones. The largest workers, called majors, do most of the nest building and foraging and are the first to fight intruders. The minor workers are smaller and tend to the nest’s brood and the queen. Most colonies have a single mature queen, which is only slightly larger than workers and has wings until she mates. Weaver ants are relatively large: the major workers reach a length of about 8 mm (0.3 inch). The ants vary in color from pale yellow to yellow-brown to reddish brown, depending on locality. Weaver ants in Australia and certain other places typically have green abdomens (gasters).
Given that ants are cold-blooded, the position of the nests in sunny trees gives weaver ants certain advantages over ground-dwelling ants. Weaver ants’ access to the warmth of sunlight enables them to spend more time foraging and accelerates the development of their young. The arboreal ants can easily move between the close-growing trees in their forest habitats, and they often use vines and lianas as bridges and pathways. When gaps are encountered, the workers grab one another with their mandibles and use their own bodies to form bridges. A downside of their arboreal existence is that colonies must relocate if their nests become shaded, and their living nests need constant repair.
Equipped with sharp mandibles and good eyesight, weaver ants are efficient—if grisly—hunters. They attack a variety of other insects, including ground-dwelling ants unfortunate enough to forage in weaver ant territory. Victims are often drawn and quartered and sometimes burned with acid. A small group of weaver ants will use their mandibles to grab onto different parts of an insect and then stretch it and pull it apart. In addition, they use the hooked claws on the ends of their tarsi to help them grasp and pull. If the prey is particularly difficult to dismember, weaver ants will expel formic acid from their abdomens onto the insect’s joints to make their work easier. They take the insect parts home to their nest for consumption.
In addition to insect prey, weaver ants eat honeydew, a sweet liquid waste excreted by some sap-sucking insects, such as mealybugs, aphids, and scale. To maintain a ready supply of honeydew, weaver ants act as ranchers of small herds of these insects, guarding them against predators such as ladybugs and spiders.
“Industrious as [weaver ants] are, their courage, if possible excels their industry; if we accidentally shook the branches on which such nest was hung, thousands would immediately throw themselves down, many of which falling upon us made us sensible of their stings and revengeful disposition, especially if, as was often the case, they got possession of our necks and hair, their stings were by some esteemed not much less painful than those of a bee; the pain, however, lasted only a few seconds.”
Although they lack stingers, weaver ants are aggressive and territorial, and they vigorously defend their nests with sharp bites. When they are on defense, they can curl their abdomens up and over their heads to expel formic acid at intruders, and they release alarm pheromones to summon reinforcements.
Use as biological control
Weaver ants have proved to be an important component of sustainable agriculture in areas throughout their natural range. They have been used by farmers in China for at least 1,700 years—the oldest known use of insects for agricultural biological control. Farmers place weaver ant nests in crop trees, including cashew, mango, lychee, Citrus, and cacao, to control insect pests such as fruit flies, thrips, and tea mosquito bugs. An effective and cost-efficient alternative to synthetic pesticides, this natural pest control helps prevent damage to crops, reduces viral and fungal diseases spread by such insects, and improves crop yields and quality. The ants can, however, also prey on pollinators and protect harmful scale, aphids, or mealybugs, and they are aggressive toward farm workers harvesting the fruits.