How Weaver Ants Use Their Own Larvae as Silk Glue Guns to Stitch Leaves Into a Nest

Oecophylla smaragdina, the Asian weaver ant, called green ant across much of South and Southeast Asia, builds its nest entirely from living tree leaves, bound together with silk it does not produce itself. The silk comes from larvae. Worker ants hold the larvae between their mandibles and move them back and forth across a leaf seam, the way a human hand might run a hot glue gun along a joint. The larva, still weeks away from metamorphosis, secretes silk from labial glands in its head. It has no say in the matter.
Before the silk phase begins, the colony solves a harder problem: pulling two separate leaves into contact. A single ant cannot span the gap between leaves on different branches. So chains form. One ant grips a leaf edge with its mandibles and holds its body rigid. A second ant grips the first ant's waist. A third grips the second. The chain extends until enough ants have linked to bridge the gap and drag both leaves close enough to touch. Researchers studying Oecophylla in Malaysian and Indian rainforests have documented chains of up to 20 workers operating in coordinated tension simultaneously. Once the leaves are held in position, a separate group of workers arrives with larvae and begins the silk-laying pass. The larva's silk hardens on contact with air, bonding the leaf surfaces within seconds. A completed nest chamber may contain dozens of such seams, each laid in overlapping passes for structural strength.
The larva's labial glands are the same glands it would normally use to spin its own cocoon during pupation. Larvae that are used heavily as silk sources sometimes produce thinner cocoons or none at all. The colony, however, gains a nest that is waterproof, structurally flexible, and capable of being repaired within hours of damage. A study published in the journal Insectes Sociaux found that Oecophylla nests can withstand sustained rainfall and wind loads that collapse the paper nests of competing species. The trade-off is entirely on the larva's side. The colony does not appear to compensate it in any measurable way.
Most social insects that build with silk, spiders aside, which are not insects, spin it themselves as adults. The use of a larva as an external silk-dispensing tool is documented in only a handful of species globally. Oecophylla is the most studied. The behaviour requires the adult workers to have already evolved the motor pattern of moving the larva in controlled sweeping motions, which is distinct from any movement they use for foraging, defense, or brood care. Entomologist Bert Hölldobler, who spent decades studying ant sociality, described this larval manipulation in Oecophylla as one of the clearest examples of tool use in social insects, a category most researchers had long assumed applied only to vertebrates.

Oecophylla smaragdina is common across the Western Ghats, Odisha, Assam, and the Andaman Islands. In Tamil Nadu and Kerala, the ants and their nests appear in mango, jackfruit, and cashew orchards. Farmers in these regions have a complicated relationship with the species: the ants aggressively defend territory and will bite any hand that reaches into a fruiting tree, but they also suppress populations of leaf-eating caterpillars and fruit flies. Some cashew growers in Goa deliberately leave weaver ant colonies on their trees as a biological pest control measure, a practice documented by researchers at the Central Plantation Crops Research Institute. The nests themselves, when disturbed, release a sharp formic acid smell. Children across coastal Karnataka and Kerala know the green ant by its bite before they know it by its name.