Hong Kong's Weaver Ants: They Build Nests in Trees and Use Their Larvae as Glue

Weaver ants in Hong Kong are fascinating insects that I'm surprised I never really noticed until recently. I happened upon what I thought was a fallen bird's nest while hiking along Mount Butler but realized there was no entrance that would be suitable for birds to come and go through.

That's when I began to investigate further and realized we have these incredible weaver ants in Hong Kong!

They're known for their unique nest-building skills, complex colony structures, and ecological roles. Here's an in-depth look at these remarkable ants:

Weaver ants (Oecophylla smaragdina) in Hong Kong are relatively large for ants, with males around 7 mm long and queens reaching up to 18 mm. They are easily recognizable by their yellowish-orange coloration. Despite their small size (relative to us)—less than 1 cm—they are strong and aggressive defenders of their colonies, equipped with sharp mandibles and the ability to spray formic acid to deter threats.

Here are some wild facts about weaver ant anatomy that makes them super fascinating:

Size

• Male weaver ants in Hong Kong measure about 7 mm in length.
• Queens are significantly larger, growing up to 18 mm, making them among the largest ants in the region.
• Worker ants vary in size; major workers are typically around 8–10 mm, while minor workers are about half that size, roughly 4–5 mm.

Coloration

• These ants are distinguished by their striking yellowish-orange coloration, which helps them blend into the leafy canopy where they live.

Body Structure

• Like all ants, their body is divided into three parts: head, thorax, and abdomen (gaster).
• They have large, powerful mandibles with sharp teeth, used for gripping leaves, capturing prey, and defense. These mandibles can carry up to 100 times the ant's weight.
• Their mandibles can open wide as a warning before biting, and their bite is accompanied by spraying formic acid from the abdomen, which causes a burning sensation.
• The ants have long legs and antennae that aid in precise movements and communication.
• Their feet have specialized pads called arolia, allowing them to cling to smooth surfaces and move adeptly across leaves and branches.

Eyes

• Weaver ants have well-developed compound eyes, providing good vision to navigate the complex arboreal (in the trees) environment.

Nest Construction Process

• Weaver ants build nests by pulling together multiple leaves on tree branches, stitching them into a tight, tent-like structure.
• Workers first survey and select suitable leaves, grasping leaf edges with their mandibles and pulling them toward each other or folding a single leaf.
• When the distance between leaves is too wide for one ant, workers form living chains by linking their bodies, creating bridges to pull leaves closer together.
• Once the leaves are positioned, some ants hold the leaves in place using their legs and mandibles while others fetch larvae from existing nests.
• Workers stimulate the larvae to produce silk by gently tapping their heads on the leaf seams; the larvae secrete silk threads that act as a natural glue binding the leaves securely.
• Thousands of silk threads are woven into sheets strong enough to hold the leaves together, making the nest waterproof and durable.
• Silk sheets are also spun to create entrances and outer galleries leading into the nest interior.
• The entire process can build a large nest of many leaves in less than 24 hours, depending on leaf type and nest size.

Nest Structure

• Nests vary from a single folded leaf stitched onto itself to large, complex structures made of many leaves, sometimes over half a meter long.
• Nests are usually elliptical or tent-shaped, with few internal chambers visible in smaller nests.
• The silk used is white and sometimes mixed with small particles like bark or soil to reinforce the structure.

Multiple Nests per Colony

A single weaver ant colony can have dozens or even hundreds of nests spread across one or several adjacent trees.

Colonies can be enormous, housing up to half a million workers distributed among these nests.

Multiple nests allow the colony to expand its living space and efficiently allocate resources like brood care, foraging, and defense across a wide area.

New nests are continuously built to replace old, damaged, or dying nests, especially after storms or wear.

The location and number of nests depend on tree characteristics such as canopy size, leaf size, branch arrangement, and environmental factors like temperature and wind.

Nests tend to be positioned in areas with good access to resources and protection, often closer to the trunk in smaller trees and more spread out in larger canopies.

Colony Coordination

Workers coordinate nest building and maintenance with other colony tasks like foraging and patrolling, balancing energy investment.

Behavioral experiments show that multiple nests with a single queen belong to one colony, distinguished by cooperation and absence of aggression between nests.

Larvae as Silk Producers

• Only the larvae of Oecophylla smaragdina produce silk, which is entirely dedicated to nest building and maintenance, not for cocoon spinning or self-protection12.
• The larvae are carried in the jaws of adult worker ants, who gently squeeze them to stimulate silk secretion.

Silk Secretion Process

• When adult ants grasp a larva, they gently squeeze its body near the tail, causing the larva to secrete a drop of silk from specialized glands.
• The silk is produced in the larva’s labial or salivary glands, located along the posterior and lateral margins of the larva’s mouthparts.
• The silk fibers are extruded through spigots on the larva’s cuticle, which are located within grooves on its buccal cavity.

Use of Silk in Nest Building

• The adult ants pull the larvae along the edges of leaves, with the silk thread fixed at each end, effectively sewing leaves together.
• The silk acts as a glue, binding the leaves securely to form waterproof, durable nests.
• The process involves ants quivering the larvae’s heads to induce silk secretion, then drawing the silk across leaf edges to stitch them.

Altruistic Larvae

• The larvae of the weaver ant donates its silk to the colony for use to build nests instead of building its own cocoon for protection.
• In a sense, the larvae are also workers for the colony as they are transported around and used as glue guns for the benefit of the colony.

Farming Honeydew-Producing Insects

• Weaver ants actively “farm” trophobionts such as soft scales, mealybugs, aphids, leafhoppers, and treehoppers, which feed on plant sap and excrete honeydew, a sugar-rich liquid.
• The ants protect these sap-feeding insects from predators and parasitoids, effectively safeguarding their honeydew “livestock.”

Mutual Benefits

• The sap-sucking insects benefit from ant protection, which increases their survival and population growth.
• Weaver ants benefit by harvesting honeydew as a carbohydrate-rich food source, supplementing their diet alongside predation on other insects.
• This sugar intake provides essential energy for the ants, supporting their high activity levels in nest building, foraging, and defense.

Impact on Host Plants and Ecosystem

• While the ants reduce many pest populations by preying on herbivorous insects, their farming of honeydew producers can sometimes lead to increased populations of these sap feeders.
• In some cases, this can facilitate outbreaks of honeydew-producing pests, which may harm plants or vector plant diseases.
• However, overall, studies show that the presence of weaver ants generally reduces pest damage and increases crop yields in tropical fruit and nut trees like mango, cashew, and cacao.

Ecological Role

• Weaver ants’ farming behavior is part of a complex ecological interaction where they act as both biological pest controllers and mutualists with certain sap-sucking insects.
• This balance allows them to maintain their energy needs while providing valuable ecosystem services in agricultural and natural environments.

Weaver ant eggs and larvae are a popular delicacy in many parts of Asia, including Thailand, Laos, India, China, Vietnam, Indonesia, and the Philippines. These larvae and pupae, which are the future queen ants, are prized for their smooth texture and rich nutritional content, including high protein and fatty acids. In regions like Northeastern Thailand, weaver ant larvae are so valued that their market price can be twice that of high-quality beef, contributing significantly to local economies.

The harvesting of weaver ant larvae is generally sustainable and does not harm the ant colonies, as mainly queen larvae are collected, which naturally leave the colony to form new nests. This practice allows for a dual benefit of pest control in plantations and a steady supply of nutritious food. The larvae are prepared in various ways across Asia; for example, in Thailand and Laos, they are boiled with spices or used to add a tangy flavor to dishes.

Meanwhile in India, the weaver ants themselves are cooked with chili and salt to create a potent chutney that even world-renowned chef, Gordon Ramsey, praised.