蚂蚁行为
How ants deal with the dead
10 月
When you think of ants, you might picture endless trails carrying food, or perhaps fierce battles with invaders. But today, let’s talk about something darker, yet just as fascinating: death, sacrifice, and hygiene in the world of ants.
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From Graveyards to Chemical Alarms
You may have noticed: in many ant colonies, there are dedicated zones where deceased nestmates end up: an ant “graveyards,” if you will. Unlike ours, these aren’t about mourning or ritual. For ants, they’re practical: a way to manage disease risk and keep the colony clean.
But there’s more to the story.
Some ants that become sick don’t – even can’t – remain among their sisters. They leave the colony on their own. This self-removal is a behavioral adaptation to limit the spread of contagion. It’s survival through sacrifice.
What’s impressive is that when an ant dies, her body doesn’t instantly trigger attention from her sisters. For a day or two, the corpse is often left untouched. It’s as if the colony doesn’t “know” the ant is dead… until that changes.
The Smell of Death: Oleic Acid as a Signal
One of the classic stories in myrmecology (the study of ants) is how they detect death chemically. Edward O. Wilson and colleagues discovered that when a dead ant’s body begins to break down, it releases oleic acid, a fatty acid that acts like a chemical death notice.
In fact, Wilson performed a striking experiment: if you dab a live ant with oleic acid, her colony treats her as if she’s dead and carries her off. In ant society, smelling like a corpse is the same as being one.
So, the delay in corpse removal isn’t neglect. It’s chemistry: the body must degrade slightly before it begins emitting this “dead ant” signal.
When Death Spreads Danger
We often assume ants remove dead nestmates just for hygienic purposes, to prevent diseases from spreading. But a landmark study raised doubts about that assumption.
In experiments where researchers introduced a fungus-infected dead ant into a colony of Camponotus castaneus, about 84 % of the ants eventually became infected just by contact with the cadaver. The entire colony was at risk. This outcome suggests that simply removing corpses is not always enough to stop disease spread.
Still, some species rely heavily on grooming behavior. By licking and cleaning themselves and each other, they can reduce pathogen transmission by up to 70%. Infected ants may also isolate themselves, reducing contact.
Funeral Styles Across Species
The behaviors ants employ around death are surprisingly varied. A comprehensive review of 55 ant species classified their “funeral rituals” into several categories:
- Necrophoresis (the removal of dead ants) — practiced by ~32 species (≈ 60 %)
- Intraspecific necrophagy (eating dead nestmates) — ~11 species (≈ 20 %)
- Burial or covering corpses — ~4 species (≈ 7 %)
- Avoidance (simply staying away from dead ants) — ~3 species (≈ 5 %)
- Self-euthanasia (ill ants leaving to die apart from nest) — rare, but present in some species
Some combine multiple strategies. For instance, 蝾螈(Solenopsis invicta) may carry, bury, or sometimes avoid corpses entirely. ResearchGate+1
Other species, like 福尔马林(Formica polyctena), will both remove and compost corpse remains outside the nest rather than consuming them outright. ResearchGate
In a more recent study on 福尔马林(Formica polyctena), researchers found that ants could distinguish corpses with different risks of infection and alter their handling behavior. For example, during periods of starvation, cannibalistic necrophagy (eating dead nestmates) increased but only when the corpses were judged “safe enough” to consume. Nature
Sacrifice, Combat, and Self-Destruction
Ant societies often push individuals to the limit. Some soldier ants throw themselves into battle, laying down their lives to protect the colony.
Even more extreme: certain species perform suicidal defense tactics. They may rupture themselves to spray toxins, block entrances, or even explode to stop intruders. Such self-sacrifice may sound extreme, but in ecological terms, it’s shaped by kin selection: the principle that sacrificing oneself can benefit closely related colony members, and thus propagate shared genes.
Similar behaviors appear in other social animals too (wolves, lions, etc.). It’s a theme: the group over the individual, when the stakes are high.
What We Still Don’t Know
Ant societies often push individuals to the limit. Some soldier ants throw themselves into battle, laying down their lives to protect the colony.
Even more extreme: certain species perform suicidal defense tactics. They may rupture themselves to spray toxins, block entrances, or even explode to stop intruders. Such self-sacrifice may sound extreme, but in ecological terms, it’s shaped by kin selection: the principle that sacrificing oneself can benefit closely related colony members, and thus propagate shared genes.
Similar behaviors appear in other social animals too (wolves, lions, etc.). It’s a theme: the group over the individual, when the stakes are high.
