Dead end

When nature decides to call it quits.

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As a child, I learned that lemmings commit mass suicide from a Disney nature documentary, White Wilderness. There they were, the poor pessimists, huddled atop a vertiginous sea cliff, driven there “by an unreasoning hysteria”, narrator Winston Hibler assured me. “This is the last chance to turn back, yet over they go, casting themselves out bodily into space.”

The lemmings, apparently, were desperate to escape the crush of overpopulation—propelled by their own profusion into the sea. I was a young adult before I discovered that Disney had lied. The lemmings had been pushed, not by wretchedness, but by wranglers. They were not leaping into the sea; they were tumbling, unwilling, into a river in landlocked Alberta, Canada, where lemmings do not live. They were not committing suicide; they were being murdered.

The fact is, accounts of animal suicide down the ages have often come down to either contrivance or wilful misinterpretation. In 1874, a correspondent to Nature explained that a captive scorpion had “turned up its tail and plunged the sting, quick as lightning, into its own back… sure enough in less than a minute life was quite extinct.”

Reading further, the experiment showed only that, if you torment a scorpion with a searing beam of focused sunlight through a magnifying glass, it might just “run hurriedly about the cage, hissing and spitting in a fierce way”, before thrashing so violently that it stings itself.

Animal suicide fascinated Victorian intellect, which variously invoked it to support campaigns against animal cruelty, notions of shared suffering, and, in the case of Darwinists, ancestral brethren. In 1845, The Illustrated London News lamented the ‘Singular Case of Suicide’ of a “fine, handsome and valuable black dog, of the Newfoundland species”. The dog had apparently been morose for days, before witnesses saw him “throw himself in the water and endeavour to sink by preserving perfect stillness of the legs and feet”.

Despite being rescued several times, the dog seemed determined to end it all, repeatedly plunging back into the sea, until he, “by dint of keeping his head determinedly under water for a few minutes, succeeded at last in obtaining his object, for when taken out this time he was indeed dead”.

In 1879, the eminent psychiatrist Henry Maudsley dismissed the verdict of suicide as a trampling of reason by romanticism: “It is quite possible,” he wrote in the journal Mind, “that an animal in a state of excitement or delirium from pain and illness may make a frantic rush that issues in its death, just as a human being may do; but this is quite a different thing to a distinctly conceived and deliberately perpetuated suicide.”

All the same, those of anthropomorphic bent seem determined not to let such level-heads spoil their mythology.

Toxoplasma gondii has just one cell, but so far the parasite has infected 30 to 50 per cent of the world’s population, as well as all warm-blooded animals. Not even the sea is safe: whales and dolphins have it too. However, Toxoplasma has only one definitive host—cats. In felines, it can reproduce and form oocysts, thick-walled sleeper cells in which the parasite hibernates in safety for up to a year. Toxoplasma rewires the brains of infected rodents, reducing their sensitivity to cats’ scent—thus increasing the chances of a rodent host being eaten by a cat and allowing the parasite to reproduce.

At Milton, near Dumbarton, Scotland, a granite bridge spans the Overtoun Burn. Each end warns dog walkers: “Dangerous bridge—keep your dog on a lead.”

This is because, in the past six decades, some 600 dogs have jumped from the Overtoun Bridge. For more than 50 dogs, it was their last leap, onto rocks 15 metres below.

The dogs were driven mad, people said, by the presence of the ghost of Lady Overtoun, widow of the baron who built the bridge, sleepless since the death of her husband in 1908. Others said the dogs suffered from a surfeit of empathy and were compelled to self-destruction by the suicidal tendencies of their owners. Another theory held that the dogs’ judgment was jumbled by high-tension wires or a nearby nuclear installation.

All the deaths had happened on clear, sunny days, and all involved long-nosed breeds such as retrievers and collies. Animal behaviourist David Sands noted that mink, a particularly pungent member of the ferret family, were reported as breeding in numbers at Milton right about when the dog deaths began in the 1950s. Searches under the bridge confirmed that mink had been calling it home ever since, while a test of the ill-fated dog breeds found a predilection for the scent of mink.

The Overtoun Bridge features low granite walls, perhaps a metre high at most, but enough to block a dog’s vision. This meant, argued Sands, the dogs were stimulated more than ever by the musky smell coming from the bridge’s piers. They had no inkling of the void on the other side of the wall, and couldn’t look before they leapt.

(In an online poll by the Daily Mirror, twice as many people preferred the ghost explanation to the animal behaviourist’s.)

Invariably, examination of animal suicide follows very human terms of reference: suffering, bereavement, a release from cruelty or boredom. In fact, creatures can and do kill themselves every day, but for very different motives.

When their colony is threatened, the soldiers of certain termite species can rupture a gland near their neck—a self-destruction called autothysis that releases a sticky goo to mire marauding ants. Behaviourists call this altruistic suicide—self-sacrifice for the good of the colony, and by extension, the martyr’s genes.

Malaysian worker ants perform the same trick, and evolutionary biologists think that, while many ants once had venomous stings, autothysis has been selected for instead, because it takes out many more attackers than a simple fight to the death. Other soldierless, termite species simply blow themselves apart, cleaving the joint between head and abdomen to block the galleries of their nests with corpses.

Auto-detonation is a common theme in invertebrate suicide: when threatened by a ladybird, the pea aphid explodes with such force that the predator is often killed in the blast. The forfeiture of one allows the escape of the many.

Other apparent suicides turn out to be a case of enslavement of the mind. Certain parasites can manipulate the chemistry of hormones in the brain of their intermediate host, altering its behaviour so that the parasite can reach its ultimate host, where it can finally breed. The protozoan parasite Toxoplasma gondii can reproduce only inside cats, and to get there, it scrambles vasopressin-related genes in the amygdala of a mouse. Ordinarily, mice are highly averse to chemical cues emitted by cat urine, but T. gondii makes them oblivious to their peril, and far more likely to be caught and eaten.

A parasitic fungus, Ophiocordyceps, overturns the minds of ants, bending them to its will. The host ant picks up fungal spores while feeding, and once the cells reach its head, they release chemicals that hack into its central nervous system. The zombie ant is then compelled to climb high to a suitable germination site, where it clings tightly onto a twig. It is a death grip: the fungus kills the ant, then grows a stalk from the back of its victim’s head, bearing more spores to begin the cycle anew.

Some female spiders allow their young to devour them, and male praying mantises will continue to copulate with a female that is eating them, but this isn’t borne of any desire to end it all—it’s a compunction to start it all. A study conducted by Macquarie University in Sydney found that cannibalistic female mantises produced many more eggs than those that let their lovers walk away, and those eggs were enriched with greatly more male-derived amino acids.

If you accept a fundamental definition—the act of killing oneself deliberately—then yes, we might semantically allow that other creatures practise suicide, but we’d need to presume that a spider, or a lemming, bears an awareness of mortality. Avoiding or accepting predation may not be the same thing as fearing or inviting death.

No one has yet been prepared to grant other animals the full spectrum of consciousness, so as far as anybody knows, suicide remains a uniquely human act.

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