Entire colonies of Kangaroo Island ants do a perfect job of playing dead to avoid predators

Scientists made a new discovery on Kangaroo Island. A species of ant has been observed exhibiting a unique behavior – playing dead – which researchers believe is a world-first recorded instance of such behavior in ants. 

University of South Australia researchers stumbled upon a colony of Polyrhachis femorata ants during routine checks of pygmy-possum and bat nest boxes on the island, initially mistaking the motionless insects for dead specimens.

This surprising discovery, published by CSIRO, marks not only the first recorded instance of an entire colony of ants feigning death but also the first record of the Polyrhachis femorata species in South Australia. The researchers suspect that the ants were “playing dead” as a defensive strategy to avoid potential threats (see image here).

Professor S. ‘Topa’ Petit recalls her astonishment upon discovering the seemingly deceased Kangaroo Island ants “The mimicry was perfect,” she explains. “When we opened the box, we saw all these dead ants…and then one moved slightly.” 

Behavior never before observed by scientists

Petit further notes that while defensive immobility is known to occur in a few ant species – either in individuals or specific casts – there is no previous record of this behavior being observed in entire colonies.

According to Petit, the triggers for this death-feigning behavior are challenging to comprehend, as it varied among the ants in the nest boxes. “In some of the boxes containing colonies of Polyrhachis femorata, some individuals took a while to stop moving, and others didn’t stop,” she says.

This fascinating discovery presents a unique opportunity for researchers to study the ants’ death-feigning behaviors. The phenomenon is of great interest to behavioral ecologists investigating a diverse range of animal species.

How this accidental discovery was made

The discovery was made as part of the Kangaroo Island Nest Box Project, an initiative aimed at monitoring wildlife recovery following the devastating 2020 bushfires. The project involves tracking 901 box cavities across 13 different properties on the island, providing valuable data on the local ecosystem and its inhabitants, including these remarkable Kangaroo Island ants.

Peter Hammond, a researcher at the Kangaroo Island Research Station, says that he used to call the Nest Box Project “Friends of the Invertebrates,” because invertebrates were often the only occupants of the bat and pygmy-possum nest boxes. “We are learning a lot about invertebrates as well as targeted vertebrates,” Hammond says.

“Most of our several hundred boxes are on burnt ground, but we also have some on unburnt properties as controls because our aim is to determine the value of nest boxes in bushfire recovery.”

“Polyrhachis femorata is strongly associated with the critically endangered Narrow-Leaf Mallee community, where it colonized several boxes very quickly. However, we also have records for two other properties further west, indicating that the ants will use other habitats.”

“We believe that the Polyrhachis femorata species was strongly affected by the bushfires.”

Many questions left unanswered about Kangaroo Island ants

Professor Petit says there is a lot to discover about Kangaroo Island ant species. “Polyrhachis femorata is a beautiful arboreal ant that tends to be quite shy, but little else is known about its ecology or behavior.”

“We have a relatively unknown world of ants under our feet and in the trees. Ants provide crucial ecosystem services and are a vital part of functional ecosystems on Kangaroo Island and elsewhere.”

“It is very exciting that such an endearing species as Polyrhachis femorata is living on Kangaroo Island and we look forward to finding out more about its ecology.”

“We have no doubt that other ants with similar death-feigning behaviors will be discovered in Australia, but it is thrilling to be among the pioneers,” says Petit.

More about Kangaroo Island ants (Polyrhachis femorata)

Taxonomy and Morphology

Polyrhachis femorata belongs to the genus Polyrhachis, which consists of more than 500 species of ants distributed throughout the Old World tropics. These ants are commonly referred to as “spiny ants” due to the presence of prominent spines on their bodies. Polyrhachis femorata is characterized by its distinctive, elongated and curved spines on the thorax, as well as its dark, metallic body coloration.

Distribution and Habitat

The Polyrhachis femorata species is primarily found in Australia, with its range extending to parts of Southeast Asia. These ants typically inhabit tropical and subtropical regions, where they build nests in the soil or construct arboreal nests using plant materials. In South Australia, the ants were recently discovered on Kangaroo Island, living in nest boxes designed for pygmy-possums and bats.

Ecology and Behavior of Kangaroo Island ants

Polyrhachis femorata ants are known for their industrious nature and their ability to adapt to different environments. They are omnivorous, feeding on a variety of food sources, including insects, plant material, and honeydew secreted by aphids. These ants have also been observed tending to aphids and other hemipteran insects for their honeydew, providing protection to the insects in return for their sugary excretions.

The most striking behavioral characteristic of Polyrhachis femorata, however, is their ability to play dead as a defensive strategy. This phenomenon, known as “death-feigning” or “thanatosis,” has been observed in a few other ant species but never before in an entire colony. Researchers believe this behavior may help the ants avoid potential threats, such as predators or other competing ant species.

Implications of Death-Feigning Behavior

The discovery of death-feigning behavior in Polyrhachis femorata has important implications for our understanding of ant ecology and evolution. This behavior could be an adaptive strategy, allowing the ants to survive in their competitive environments by avoiding confrontations with predators or other threats.

Additionally, the discovery of this behavior provides a unique opportunity for researchers to study the underlying mechanisms and triggers that prompt such a response. By understanding the factors that influence this behavior, scientists may be able to gain valuable insights into the evolutionary forces that have shaped the complex social structures and communication systems of ants.

Conclusion

Polyrhachis femorata is a remarkable ant species with a unique and fascinating behavior: playing dead as a defensive strategy. As researchers continue to study these ants and their death-feigning behaviors, we are likely to gain a deeper understanding of the complexity of ant ecology, evolution, and behavior. This discovery also serves as a reminder of the incredible diversity of life on our planet and the endless possibilities for scientific discovery that await us in the natural world.

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