Earth’s geomagnetic field is a poorly understood natural phenomenon without which life as we know it wouldn’t exist. It diminishes deadly solar radiation and, among others, mole rats and supersonic jet pilots use it to navigate. Cockroaches tap into the global magnetic field too, if not for navigation — because they don’t migrate or fly planes — then for spatial orientation.
Now an international team of physicists has won the prestigious 2019 Ig Nobel prize for biology for their paper investigating the biomagnetic properties of American cockroaches. They discovered, to their shock, that when a cockroach is magnetized it generates a little magnetic field, which takes roughly an hour to decay - unless roach is dead. Then it takes two to three days for the field to decay.
The original paper feted at the Ig Nobels appeared in Nature in 2018.
Why would an international team of physicists in Singapore, Australia, China and Poland investigate the magnetic fields emitted by magnetized cockroaches at all, let alone live ones versus dead ones? The team says it proved the validity of its measurement method, which could be used for things other than magnetic fields. Or:
“We are all physicists with a background in quantum optics,” co-author Herbert Crepaz of Nanyang Technological University told Haaretz. “In discussions with theorists, it was mentioned that there are indications of quantum effects in living organisms, with magnetoreception among them. ... We built one of the most sensitive magnetometers [anywhere] and then were asking ourselves what would be interesting to measure with it.”
The answer, evidently, was unsolved problems in despised insects, which apparently house their magnetic particles in their hindgut, not in their brains like so many other living creatures.
Actually, the wonders of our own human utilization of the geomagnetic field is only now coming to true light — blue light. “Starved men, but not women, significantly oriented toward the ambient/modulated magnetic north or east, directions which had been previously food-associated, without any other helpful cues” – but only under conditions of blue light, a team wrote this February in PLOS One.
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Yes, they showed that male humans need blue light to be geomagnetically oriented. Sounds like the more we know about geomagnetics, the better.
Back to the roach. The researchers had set out to characterize the biomagnetic properties of the American cockroach (Periplaneta americana), alive or dead. The americana throngs Singapore, home to most of the team, says Crepaz, explaining the choice of bug. Also, as he points out, the Periplaneta’s magnetoreception talents have been documented.
They had not expected to find a major difference in the decay times of the magnetic field alignment in dead cockroaches compared with their still-breathing peers. “The magnetic particles themselves do not change or disappear in a corpse,” he points out. Yet they did find a major difference.
Cockroaches tap into the planet’s magnetic field using the unwitting power of sensory magnetoreception. You do too, in order to orient yourselves (though we use our brains, not our behinds). Magnetoreception is achieved by particles of magnetite, i.e., iron oxide, in our brain cells.
Magnetite is a naturally occurring mineral that reacts to magnetic fields by change of molecular orientation. In the roaches, possibly the magnetic nanoparticles in its butt are greigite — a sulfur-based equivalent to the iron oxide magnetite.
Their magnetic particles can, it turns out, be exploited to render roaches magnetic, as one does.
One magnetizes cockroaches by applying a magnetic field to them. As the cockroaches are thusly rendered magnetic, the magnetic particles in their rears become (partially) aligned, like compass needles. But you shouldn’t use them as fridge magnets, if only because their magnetic field isn’t perpetual. It decays.
One knows the magnetic field the roach generates decays because one measures the signal using a highly sensitive magnetometer.
Live roach: fast field decay. Dead roach: much, much slower field decay. (Occasionally, in live roaches, the magnetic field would strangely reverse from its decay trajectory. We shall ignore that anomaly, as the team pretty much did.)
Once our cockroaches are magnetized, the field generated by live ones is more intense than the field generated by dead ones. But even with that factored in, the magnetic nanoparticles in live cockroaches and dead cockroaches behave vastly differently.
Why would the magnetic field emanating from a dead cockroach decay more slowly?
Because the innards of a dead cockroach dehydrate, increasing environmental viscosity within the cells, the team of quantum physicists discovered. The magnetic particles lose their uniform orientation, moving at random, more slowly.
In other words, the inside of the dead, inert cockroach is gummier than the inside of a live, metabolizing cockroach. Makes perfect sense when you think about it.
Although they would have eaten anything — garbage if given their druthers — the test cockroaches were fed on cat food (in case you want to repeat the experiment). The live ones were first immobilized by being subjected to 4-degree Celsius temperatures, while tests on the dead ones were run at least two days after their demise.
The paper "makes you wonder if there’s a difference between cockroaches and human beings," Marc Abrahams, co-founder of the Annals of Improbable Research, the journal behind the Ig Nobels, told Haaretz. Indeed, this is the kind of paper that makes one laugh, then think, as his organization aspires to achieve.
So how did Crepaz feel at being awarded an Ig? At first he had mixed feelings, he tells Haaretz, “given that there were some really weird cases. But then reading more about it, I was thrilled to get this prize and had a great experience at the ceremony.”
So does it make sense to use a dead magnetized cockroach as a fridge magnet? No.
But it does make sense that the cockroach would find the stimulus from external magnetic fields annoying. So yes, if you can build a magnetic field generator strong enough, they might be deterred from your kitchen. And if that works, you might get an Ig Nobel for it.