Researchers at Nanyang Technological University, Singapore (NTU Singapore) have shown that while cockroaches contain magnetic particles they do not use them for navigation, contrary to what was previously believed.
Previous studies suggested that cockroaches can sense and interact with the Earth’s magnetic field and showed that they can become magnetised themselves if they stay too long near magnets. A leading scientific explanation for the sensing was that cockroaches use special cells containing rotatable small magnetic particles, similar to tiny compasses.
Using a highly sensitive atomic magnetometer, researchers Associate Professor Rainer Dumke and Assistant Professor Tomasz Paterek, both professors at NTU’s School of Physical and Mathematical Sciences, studied the phenomenon on the American cockroach[1], a common cockroach species in Singapore.
They found that the microscopic magnetic particles rotated too slowly to influence their navigation.
Assoc Prof Dumke said, “It was a common belief that some insects have a form of magnetised navigation mechanism. Our research now substantiates the claim that cockroaches might have another form of magneto-reception mechanism, opening the door for further studies on insect navigation and even bio-sensor applications.”
“Our interdisciplinary research blends entomology and physics to resolve important magneto-reception questions using an unconventional medium – that is, the humble cockroach. It also enhances existing research on how biological organisms sense magnetic fields,” said Asst Prof Paterek.
For their discovery and contribution to understanding how animals sense magnetic fields, the NTU researchers received the Ig Nobel Prize in a ceremony today at Harvard University in the United States. Presented by Nobel laureates, the award celebrates the unusual, honours the imaginative, and spurs people’s interest in science, medicine, and technology.
The study was published in 2018 in Scientific Reports, an international peer-reviewed journal.
To measure the cockroaches’ response to magnetism, the researchers used a highly sensitive atomic magnetometer that can detect magnetic fields ten billion times smaller than the Earth’s.
The magnetometer was an earlier project of Assoc Prof Dumke’s team, through his joint appointment as a Principal Investigator with the Centre for Quantum Technologies at the National University of Singapore. The quantum device measures small magnetic fields by looking for changes in how a laser beam interacts with a gas.
“Whenever scientists come up with new technology, that technology is likely to find applications we could never have predicted at the outset of the research. Using an atomic magnetometer to study the magnetism of cockroaches is an excellent example of an unexpected use case for a quantum device,” said Artur Ekert, Director of the Centre for Quantum Technologies.
How the study was done
The NTU research team exposed both living and dead cockroaches to a magnetic field of three kilogauss – about a hundred times stronger than a typical fridge magnet – then measured the strength of their magnetisation and how fast it decayed.
They observed that the magnetic field around the living cockroaches decayed in about 50 minutes while it took almost 50 hours for it to decay in dead cockroaches.
Their experiment showed that cockroaches become magnetised because they contain magnetic particles that can become aligned with an external magnetic field. These particles are contained in a viscous fluid within the living cockroaches.
However once the insects die, the fluid starts to harden, increasing its viscosity and slowing the random movement of magnetic particles out of their alignment, and thus slowing magnetisation decay.
Based on the 50 minute decay times in living cockroaches, the researchers conclude that the magnetic particles in cockroaches are not responsible for cockroaches’ magnetic field-sensing abilities, since that is too slow to account for their receptiveness to magnetic fields that rotated every 10 minutes in previous behavioural experiments.
Building on the findings, the researchers will continue studying the insects to find a clear and distinct explanation on their response to magnetic fields.
Note to Editors:
Paper titled “In-vivo biomagnetic characterisation of the American cockroach” published in Scientific Reports in March 2018.
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[1] The American cockroach, Periplaneta Americana (Linnaeus), is the largest of the common cockroaches measuring about 3-4 cm in length. They are reddish brown and immature cockroaches resemble adults except they are wingless. They are commonly found across southern United States, especially Florida.