Ants exhibit many fascinating behaviors, including the methodical removal of deceased nestmates. This act serves a fundamental purpose for the colony, highlighting a sophisticated aspect of ant social life.
The Curious Case of Necrophoresis
The behavior of ants carrying away their dead is known as necrophoresis, a term introduced in 1958 by scientist E.O. Wilson. This hygienic practice involves removing dead individuals from the colony, often by carrying them to a designated refuse pile. Necrophoresis is also observed in other social insects like bees, wasps, and termites. When an ant encounters a deceased nestmate, it inspects the body with its antennae before transporting it with its mandibles.
Why Colony Hygiene is Paramount
Ants primarily engage in necrophoresis to prevent disease spread within their densely populated colonies. Dead ants are breeding grounds for harmful pathogens like bacteria and fungi. These microorganisms pose a significant threat, as infections can rapidly spread through a confined ant nest, potentially wiping out a large portion of the population. Removing deceased individuals minimizes the colony’s exposure to these threats, safeguarding the group’s health. Studies show that colonies prevented from removing corpses experienced increased worker mortality.
The Chemical Cues Guiding Disposal
Ants detect their dead and initiate removal through specific chemical signals. When an ant dies, its body undergoes decomposition, releasing fatty acids like oleic acid and linoleic acid. These act as “death cues,” signaling to living ants that a nestmate is deceased and needs disposal. Live ants coated with these fatty acids have even been carried away by their nestmates, demonstrating the powerful influence of these chemical signals.
The detection of death cues is often coupled with the disappearance of “life signals” present on living ants. Compounds like dolichodial and iridomyrmecin are present on the cuticle of live ants and act as chemical indicators of life. Necrophoresis is triggered when these life signals diminish or disappear, unmasking the death cues. While some species may remove corpses within an hour, in others, it can take anywhere from one to six days for the chemical changes to fully manifest and prompt significant corpse removal. This intricate chemical communication ensures that ants accurately identify and remove only those individuals that pose a hygienic risk.
Implications for Ant Colony Health
Necrophoresis is a sophisticated adaptation contributing to the health and resilience of ant societies. This collective hygienic strategy is part of “social immunity,” where the group employs behaviors to combat disease. For social insects in close quarters, effective waste management prevents outbreaks. Some ant colonies even have specialized “undertaker ants” responsible for corpse removal. This act highlights the complex and organized nature of ant colonies, allowing them to thrive in dense environments.