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The Curious Case of Cockroach Magnetization

Birds are the best-known instance of creatures in a position to sense magnetic fields and to make use of them for orientation and navigation. Much less well-known are the magneto-sensing skills of American cockroaches, which shortly develop into magnetized when positioned in a magnetic area.

Simply how these creatures use this skill is the topic of a lot hypothesis. However there’s basic settlement that a greater understanding of biomagnetic sensing may assist engineers design higher sensors for different functions, equivalent to microrobot navigation.

However earlier than that may occur, engineers will want a much better understanding of how cockroaches sense magnetic fields and the way they develop into magnetized themselves.

Enter Ling-Jun Kong at Nanyang Technological College in Singapore and some friends who’ve measured the way in which American cockroaches develop into magnetized. Within the course of, they’ve made a exceptional discovery—it seems that the magnetic properties of residing cockroaches are strikingly totally different from these of useless cockroaches. They usually assume they know why.

The experiments are simple. Kong and co positioned a collection of residing and useless cockroaches in a magnetic area of 1.5 kiloGauss; that’s about 100 instances stronger than a fridge magnet. The group left the creatures within the area for 20 minutes after which measured how strongly that they had develop into magnetized and the way lengthy it took for this magnetization to decay.

The outcomes make for fascinating studying. The group may simply measure the magnetic area related to all of the cockroaches, alive or useless, as quickly as they got here out of the exterior area. The sector related to residing cockroaches then decayed in about 50 minutes. Against this, it took virtually 50 hours for the sphere to decay in useless cockroaches.

That raises an apparent query: why the distinction? Kong and co have created a mathematical mannequin of magnetization to give you the reply. They assume that magnetization is the results of magnetic particles contained in the cockroaches aligning themselves with the exterior magnetic area. When faraway from the exterior area, the magnetization decays as a result of Brownian movement causes the magnetic particles to develop into randomly aligned once more.

However additionally they examine how the time this takes varies in keeping with the viscosity of the medium the particles are trapped in. They present that the decay time will increase because the viscosity of this medium will increase and turns into extra glassy.

This implies a solution to the conundrum. Cockroaches develop into magnetized as a result of they comprise magnetic particles that develop into aligned with an exterior magnetic area. These particles are trapped in a runny medium that has low viscosity in residing cockroaches. However as quickly because the creatures die, the medium begins to harden and its viscosity will increase. That’s what causes the decay time to extend.

That’s fascinating work that helps to reply some essential questions on the way in which cockroaches work together with exterior magnetic fields. But it surely leaves loads of mysteries.

First is the query of the character of the magnetic particles—what are they? Biologists have discovered tiny particles of the magnetic mineral greigite (a sort of iron sulphide) in ants, bees, and termites.

So it might be that cockroaches additionally comprise particles of greigite. Certainly, Kong and co’s outcomes are suitable with the presence of greigite particles with a radius of 50 nanometers or so however the outcomes rule out the presence of associated magnetic minerals equivalent to magnetite.

One other query is the place such particles would possibly come from. Are they contaminants picked up by the cockroaches from their atmosphere or are they biogenic, fashioned by a organic course of contained in the cockroaches themselves? Kong and co are unable to reply this.

Nevertheless, they will throw some gentle on how cockroaches would possibly use this type of magnetization. They are saying that the decay time of 50 minutes in residing cockroaches is simply too sluggish to be of any organic use. “Our information and mannequin present that these magnetic particles can’t be liable for magnetic sensing,” they are saying.

So if cockroaches do exploit magnetic sensing, they have to use another mechanism. The main contender right here is the unconventional pair mechanism during which a magnetic area influences the result of a chemical response.

Many biophysicists take into account this the one mechanism that may realistically affect residing creatures on a time scale that may be biologically helpful. Maybe cockroaches use this, too. “Our experiment supplies assist for different types of magneto-reception, e.g. the radical-pair mechanism,” say Kong and co.

That’s fascinating work that might be a stepping stone to raised understanding biosensing of magnetic fields and of exploiting this skill in future generations of sensors.

Ref: arxiv.org/abs/1702.00538: In-Vivo Biomagnetic Characterisation of the American Cockroach


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