Cockroaches, infamous for their tenacity, are often cited as the most likely survivors of a nuclear war. Some pundits even claim the critters can live without their heads. It turns out that this assertion is fact: at times headless roaches can live for weeks.

To understand why cockroaches—and many other insects—can survive decapitation, it helps to understand why humans cannot, says physiologist and biochemist Joseph G. Kunkel of the University of Massachusetts Amherst, who studies cockroach development. First, decapitation in humans results in blood loss and a drop in blood pressure, hampering transport of oxygen and nutrition to vital tissues. “You'd bleed to death,” Kunkel states.

In addition, humans breathe through their mouth or nose, and the brain controls that critical function, so breathing would stop. Moreover, the human body cannot eat without the head, ensuring certain death from starvation should one survive the other ill effects of head loss.

Cockroaches do not have the same kind of circulatory system as people. For blood to make its way through the vast network of human blood vessels, and especially through the tiny capillaries, a fair amount of pressure must be maintained. The roach vascular system is much less extensive and lacks tiny capillaries, Kunkel notes, so pressure can be significantly lower. “After you cut their heads off, very often their necks will seal off just by clotting,” he adds. “There's no uncontrolled bleeding.”

Moreover, the hardy vermin breathe through spiracles, or little holes in each body segment. The roach brain does not control this breathing, and blood does not carry oxygen throughout the body. Rather the spiracles pipe air directly to tissues through a set of tubes called tracheae.

Cockroaches are also poikilothermic, or cold-blooded. Consequently, they do not expend energy to heat themselves up and so can get by on much less food than humans need. They can survive for weeks after just one meal, Kunkel says. “As long as some predator doesn't eat them, they'll just stay quiet and sit around.”

Entomologist Christopher Tipping of Delaware Valley College has actually decapitated American cockroaches (Periplaneta americana)—“very carefully under microscopes,” he observes—to study what happens, among other things. “We sealed the wound with dental wax to prevent them from drying out. A couple lasted for several weeks in a jar.”

Roaches and many other insects have clumps of ganglia—nerve tissue agglomerations—distributed within each body segment, and the clumps are capable of performing the basic nervous functions responsible for reflexes, “so without the brain, the body can still function in terms of very simple reactions,” Tipping says. “They can stand, react to touch and move.”

And it is not just the body that can survive decapitation; the lonely head can keep on functioning, too, waving its antennae back and forth for several hours until it runs out of steam, Kunkel says. If given nutrients and refrigerated, a roach head can last even longer.

Still, in roaches “the body provides a huge amount of sensory information to the head, and the brain cannot function normally when denied these inputs,” explains neuroscientist Nicholas J. Strausfeld of the University of Arizona, who specializes in arthropod learning, memory and brain evolution. For instance, although cockroaches have a fantastic memory, he says, trying to teach them is futile when they have bits of their body missing. “We have to keep their bodies completely intact.”

Cockroach decapitation may seem macabre, but scientists have conducted many experiments with headless roach bodies and bodiless roach heads to answer serious questions. Loss of the noggin deprives roach bodies of hormones from glands in their heads that control maturation, a finding that is helping researchers investigate metamorphosis and reproduction in insects. And studies of bodiless roach heads elucidate how insect neurons work. Ultimately, though, the results provide one more testament to the cockroach's enviable endurance. A headless roach may not be the smartest of its kind, but it can certainly survive.

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