Ants dispose of their dead, a complex behavior known as necrophoresis. This sophisticated sanitation routine involves the removal of deceased colony members from the nest area to maintain a healthy environment for the living. Entomologist E.O. Wilson first formally described and named this behavior in 1958 after observing it in ant colonies. Necrophoresis is one of several hygienic practices that allow social insects to thrive in the high-density confines of their nests.
The Process of Necrophoresis
The physical task of corpse removal is often handled by specialized individuals within the colony, sometimes referred to as undertakers or mortician workers. These workers show a tendency to take on the role of sanitation specialists, though any worker may perform the task if necessary. The behavior is triggered when a worker encounters a dead nestmate, which it then grasps with its mandibles and carries away from the main nest structure.
The destination for the deceased varies depending on the ant species. In many species, the corpse is transported a considerable distance from the nest entrance and dropped at an arbitrary point to prevent contamination. Other colonies create designated refuse piles or “middens,” which are communal refuse dumps located either outside the nest or in a specialized, sealed-off chamber deep within the colony structure.
Why Ants Dispose of Their Dead
The function of necrophoresis is social immunity, which is the collective defense mechanism against disease. Living in large, dense, warm, and humid underground nests creates an environment where pathogens can spread rapidly between individuals. A single deceased ant represents a significant biological risk to the entire colony, making its swift removal a matter of survival.
Decomposing bodies are breeding grounds for dangerous microbes and fungi, such as the entomopathogenic fungus Metarhizium. If a fungus-infected corpse is left inside the nest, its spores can quickly contaminate the entire population, leading to colony collapse. By physically removing the source of contamination, ants drastically reduce the risk of an epidemic. Studies show workers remove corpses contaminated with fungal spores at a higher rate than uninfected bodies, demonstrating a heightened sensitivity to biological waste.
The Chemical Signal of Death
Ants do not recognize death through visual cues, but rather through a change in the deceased ant’s chemical signature. The traditional, widely studied mechanism centers on the buildup of specific fatty acids that are released as the ant’s tissues decompose. The primary chemical involved is oleic acid, often accompanied by linoleic acid, which seeps out as internal fats break down after death.
The presence of these fatty acids acts as a universal death cue, prompting any worker that detects the scent to immediately initiate necrophoresis. In a famous experiment, applying oleic acid to a healthy, living ant was enough to trigger its nestmates to treat it as a corpse and carry it to the refuse pile. However, research into species like the Argentine ant suggests a more complex mechanism may be at play, where the cue is not the presence of a death chemical but the absence of a life-associated chemical.
In this alternative model, living ants possess masking chemicals, such as iridomyrmecin and dolichodial, which suppress the necrophoric response to the fatty acids that are always present on the ant’s cuticle. When an ant dies, these masking chemicals quickly dissipate or degrade, sometimes within an hour, unmasking the ever-present oleic acid and triggering immediate removal. The time it takes for a corpse to be removed varies by species; in some, the oleic acid cue takes about two days to become strong enough, while in others, a rapid response indicates the loss of the life-signal is the overriding factor.