The Imitation Game: Does a jumping spider in the Andamans chemically mimic weaver ants?

Weaver ants are arguably one of the most dominant creatures on Earth. Across urban and wild habitats in the tropics, meticulously constructed weaver ant nests fill the trees. The masterful architects manipulate (or antipulate) leaves to form magnificent leafy structures held together by larval silk. The surreal queendoms of the canopy can stretch out to cover vast areas and consist of over a hundred nests, all working for queen and colony! Weaver ants actively manage a multi-dimensional territory from their homes in the trees. Foraging trails run vertically between the ground and the nests and horizontally between trees and plants. Foraging workers collect sugar-rich honeydew from homopterans, hunt protein-rich prey and scavenge a wide selection of food on the ground. They protect their food, territory and kin with a ferocity that makes any predator or nosy photographer think twice before venturing too close. With complex chemical communication between individuals, they can mobilise groups to retrieve food, rescue kin or neutralise threats with incredible efficiency. If all of this got you thinking that someday you would like to be as awesome as a weaver ant, some spiders are already ahead of you by several million years.

Imitation is flattery, they say. And flattery is a Trojan Horse filled with ulterior motives. 

For Myrmarachne plataleoides, that motive is clear - protection. M. plataleiodes is a jumping spider that has evolved to look almost exactly like a weaver ant! It even modifies its behaviour to fill in the gaps - the eight-legged spider lifts its front legs to look like a six-legged insect and waves them to mimic antennae. Its objective is simple: trick predators into believing it is a weaver ant, so the predator leaves the spider alone. Myrmarachne spiders, however, cannot get too close to their hosts because weaver ants rely heavily on chemical signals. When the visual copycat gets caught red-legged by weaver ants, it typically ends with fatal consequences for the spider.

The crab spider Amyciaea has a far more aggressive motive. The spider’s abdomen looks precisely like the head of a weaver ant. It uses this resemblance to lure unsuspecting worker ants before preying on them. Amyciaea spiders wiggle their abdomens near weaver ant foraging trails to seem like a worker ant attempting to communicate - weaver ants communicate through chemical signals and by making contact with each other's antennae. When an isolated ant comes close in an attempt to antennate, the crab spider turns around and makes a sumptuous meal of it.

Looking like a weaver ant is invaluable when the objective is to ward off predators or lure weaver ants from a distance. How does a mimic go deeper into this imitation game? How does the artist get close enough to safely access colony resources like food and shelter? How does the mimic convince a weaver ant that it is a fellow colony member? The answer lies in how weaver ants recognise a colonymate - a pheromone signature unique to the colony. The jumping spider Cosmophasis bitaeniata is a chemical mimic of the weaver ant - the spider can "smell" like a colony member.

How does a spider produce a fake chemical identity card for its ant hosts? The spider takes on the cuticular hydrocarbons of its weaver ant host by consuming the colony's young larvae! Studies have shown that the spider's cuticular signatures do not elicit any aggressive response from the colony’s major worker ants. This fascinating form of mimicry allows the spider to casually enter weaver ant nests and gain access to food and shelter - one study found that the spider built its eggsac within the safe walls of a weaver ant nest. In the Andaman Islands, a jumping spider from the Cosmophasis genus appears to share the same relationship with weaver ants. They go in and out of nests, often with larvae in their jaws - snacks with a purpose. They comfortably get within 2-3 cm of weaver ant foraging trails and nest sites without eliciting any aggression from the workers. In a few observations, I have seen the spider stealing planthoppers from aggregation sites where weaver ants are actively "farming" honeydew from the homopterans. This suggests the presence of kleptoparasitism in the relationship as well. All in all, a mimicry so well-crafted by a spider that, to the human eye, looks nothing like the weaver ant!

Cosmophasis spider's ability to look gorgeously colourful while tricking weaver ants may have a downside. Remember that Mymrarachne spiders often avoid predators because of their ant-like appearance. The Cosmophasis spider’s visual dissimilarity from its host means it does not enjoy any protective or defensive benefits of mimicry, particularly when faced with a visually driven predator. During one morning spent following a trail of weaver ants peppered with Cosmophasis hovering around the tree, I noticed the shimmer of a fine silk line. At the centre of the line of silk was what appeared to be a thin green stem, and at the end of that stem, a freshly eaten Cosmophasis spider. The stick-like object was the surreal Ariamnes spider. While resting, Ariamnes look like twigs suspended by a single line of silk. When active, they look like a ballerina's most vivid eight-legged rendition of 'Black Swan'.

On the species of Cosmophasis from the Andaman Islands, methods like chromatography can help definitively confirm the chemical mimicry of weaver ants. Meanwhile, incredible processes and stories like these need naturalists, researchers, enthusiasts and storytellers, all in equal measure, to explore them with the tenacity of a weaver ant looking for food.

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About the author

John is a writer, photographer and researcher with a keen interest in spiders. ​ He regularly daydreams of using a calculator, a pencil and a cup of sambar to unravel the secrets of the universe.