In 1912, Antarctic explorer Captain Lawrence Oates willingly walked to his death so that his failing health would not jeopardise his friends’ odds of survival. Stepping from his tent into a raging blizzard, he left his men with the immortal words, “I am just going outside and may be some time.” It was a legendary act of heroism but one that is mirrored by far tinier altruists on a regular basis – ants.
Like Captain Oates, workers of the ant species Temnothorax unifasciatus will also walk off to die in solitude, if they’re carrying a fungal infection. In fact, Jurgen Heinze and Bartosz Walter found that workers, regardless of the reason for their demise, take their last breaths in a self-imposed quarantine. A Temnothorax worker may spend its life in the company of millions, but it dies alone.
In nature, old age is a luxury that few individuals can afford. Most often, death comes at the hands of predators or parasites. In the latter case, dying individuals pose a massive threat to their peers. In the closely-packed, humid environment of a nest, infections can spread like wildfire. Metarhizium only becomes infectious a few days after its host succumbs – it takes that long to produce new spores. And by that point, the ants are long gone.
Heinze and Walter treated 70 workers with spores of the parasitic fungus Metarhizium anisopliae. Three-quarters of them were dead within ten days. Of these, at least 70% voluntarily left the colony either hours or even days before that point and died well away from their nestmates. Another 21% were found dead outside the nests. It wasn’t clear if they had left themselves or been evicted but certainly, the other ants don’t treat infected workers any differently.
The tiny hermits never try to return home. They don’t forage for food or water. They never try to get in touch with nestmates. If they’re returned home, they’ll actively try to flee again. As Heinze and Walter say, this appears to be “an active and, in most cases, adaptive response of the dying ant to its own condition.”
Humans aren’t the only species that have had to deal with the issue of slavery. Some species of ants also abduct the young of others, forcing them into labouring for their new masters. These slave-making ants, like Protomagnathus americanus conduct violent raids on the nests of other species, killing all the adults and larva-napping the brood.
When these youngsters mature, they take on the odour of their abductors and become the servants of the enslaving queen. They take over the jobs of maintaining the colony and caring for its larvae even though they are from another species; they even take part in raids themselves. But like all slave-traders, P.americanus faces rebellions.
Some of its victims (ants from the genus Temnothorax) strike back with murderous larvae. Alexandra Achenbach and Susanne Foitzik from Ludwig Maximillians Universty in Munich found that some of the kidnapped workers don’t bow to the whims of their new queen. Once they have matured, they start killing the pupae of their captors, destroying as many as two-thirds of the colony’s brood.