It’s taken as common knowledge that honey bees, and ants, migratory birds and sea creatures, are sensitive to the planet’s magnetic field. That they should be was first suggested at the end on the 19th century, but the first convincing evidence wasn’t produced until 1965. A research group in Frankfurt that included Wolfgang Wiltschko demonstrated that migratory European Robins could detect the geomagnetic field as a directional compass. But just exactly what did being ‘magnetosensitive’ mean?
Since then, despite not knowing exactly what animals were sensing, or how, or indeed when they paid attention to the sense itself, it’s now accepted that many animals are known to be magnetosensitive, including bacteria, honey bees, cockroaches, newts, turtles, rodents, lobsters, fish, bats, and many birds. While ‘affected by’ or ‘sensitive to’ do not automatically mean ‘use’, detecting and orienting yourself with respect to the Earth’s magnetic field could potentially be done equally well in the atmosphere, in the deep oceans, and on the ground. The magnetic field appears to be more universal and constant than any other navigational cue, so using it to get around seemed an obvious use.
What’s in a field?
Finding evidence for any organs or structures that might be involved in detecting the properties of the field and explaining how it provides information that is acted upon still proves to be very difficult. It was not a simple job either to anticipate just what kind of information could be obtained or how useful it could be. If you imagine the earth as a giant magnet then the most obvious bit of information is polarity, in our terms, a ‘North’ or ‘South’ direction. Direction though, is not location.
Two other features of the field might help. As the field curves around a globe, parallel to the surface at the magnetic equator but perpendicular to the poles, the other piece of ‘positional’ information is the angle the field makes relative to the Earth’s surface. We call that the ‘inclination’. The intensity or strength of the field also varies, but not by much, and not in any systematic way. So, while there might be some local ‘character’ that might allow you to learn to identify a unique place it’s difficult to image how field strength might be used to get you to that place.
So that’s a long way of suggesting that animals (who do not share the same needs), may be sensitive to different features (or combination of features) of magnetic fields. They may use the Earth’s magnetic field in different ways AND therefore use different ‘apparatus’ to do it. For instance, Robins apparently, sense the field inclination, and not polarity.
Bee-ing sensitive
In 1972 Martin Lindauer published a paper1 describing how the orientation of honey bees’ combs and their foraging dances could be altered by manipulating the magnetic field they could sense with a device called a helmholz-coil2. Subsequent research (based on evidence from bacteria) suggested that an iron oxide (magnetite), which could be found in all sorts of animals, would react to a magnetic field and could therefore be the basis of some sensory structure. Theoretically, if the iron could be found, somewhere close by there ought to be some link to the nervous system that would enable perception3.
The problem is that iron is an essential omnipresent component everywhere in biological cells and, since the body is transparent to magnetic fields the candidate cells could be anywhere. Worse, experimenter's labs were awash with magnetic material, contaminating their work and confounding their results4.
Hypothetical, or entangled and absurd
In honey bees two possible sites lead the field as potential locations for their magnetic ‘sense’, the anterior dorsal region of the abdomen, where evidence suggests magnetite particles are present, and in the ventral abdomen where there are iron granules in cells in the subcuticular fat layer. Few studies, or none if you want to be critical, have produced robust evidence that the presence of iron is functional in a navigational sense.
It has been suggested that exposure of live bees to an intense magnetic field alters the magnetization of the ferromagnetic particles in their abdomens so that, unlike comparable control bees, they failed to respond to an anomaly in a controlled magnetic field that signalled a sugar reward. These studies, ten or fifteen years later, are still debated and lack support; do the iron particles just represent stored dietary iron? Are the associative learning choices they faced ecologically relevant, and can the results be reproduced? At the moment magnetite-based reception is hypothesis, not theory.
In migratory birds the most useful hypothesis is quite different5. In this case the suggestion is that a magnetic field causes light photons to alter the direction of electron spin in some atoms, changing the balance of some chemical reactions between light sensitive molecules in their eyes (molecules that bees do not have). This ‘Radical-Pair Mechanism of Magnetoreception’6 involves the quantum physical phenomenon of electron ‘entanglement’ and I am not the one to explain it! There is no doubt the effect can be experimentally demonstrated, but whether in fact it is used by birds hasn’t been proved. As Richard Feynman famously observed7 (about quantum physics particularly), “I hope you can accept Nature as She is – absurd.”
Irrelevant noise?
The other research problem, especially but not just for honey bees, is that so often the ability to sense a magnetic field appears somewhat irrelevant. Some animals that do appear to respond to changes in a field do so very slowly. Despite its ubiquity, very few animals appear to rely on our magnetic field completely, if at all. If they do refer to it, its status appears relegated to ‘backup’ or ‘supporting info’, while celestial data, way-points, path-integration, image-matching and so on take centre-stage. Testing the ability in a laboratory, with all sorts of creatures, is frequently far from conclusive and needs scale and repetition.
Maybe that shouldn’t be surprising. The Earth’s magnetic field is, as far as energy goes, a pretty weak phenomenon. Thermal and electrical energy are orders of magnitude larger, and there is no obvious way in which the ‘signal’ could be amplified above the energetic ‘noise’ by something analogous to eyes or ears8. As long as they are there, there are plenty of alternative clues to your whereabouts that are faster and easier to use than a tiny magnetic field. If you are a night-migrating song bird or an ocean-going sea turtle the world is very different and there’s no alternative, but we have to ask if a magnetic sense in honey bees, if it is employed at all, is just an obsolete vestigial ability with very little contemporary ecological relevance?
*This article first appeared in the Apiarist’s Advocate, April 2025. Read more of the Advocate here.
Martin Lindauer, 1972. Magnetic Effect on Dancing Bees. Anim Orientat Navig 559–567.
Helmholtz coils are a special form of electromagnet in which a there is a pair of parallel, coaxial, wire coils separated by a distance equal to their radius. They generate a uniform magnetic field between the coils when an identical electric current is passed through each coil. The system can be ‘tuned’ to negate the effect of the Earth’s magnetic field or produce a uniform field with a known strength and direction. https://www.electricity-magnetism.org/helmholtz-coils/
Kuterbach, D.A., Walcott, B., Reeder, R.J., and Frankel, R.B. (1982). Iron-Containing cells in the honey bee (Apis mellifera). Science 218, 695–697. https://doi.org/10.1126/science.218.4573.695.
Kobayashi, A.K., Kirschvink, J.L., and Nesson, M.H. (1995). Ferromagnetism and EMFs. Nature 374, 123. https://doi.org/10.1038/374123a0.
Warrant, E.J., 2021. Unravelling the enigma of bird magnetoreception. Nature 594, 497–498. https://doi.org/10.1038/d41586-021-01596-6
Hore, P.J., Mouritsen, H., 2016. The Radical-Pair Mechanism of Magnetoreception. Annu. Rev. Biophys. 45, 299–344. https://doi.org/10.1146/annurev-biophys-032116-094545
Feynman, Richard P. (1985b). QED: The Strange Theory of Light and Matter. Princeton University Press. ISBN 0-691-02417-0. Transcribed from Richard P Feynman's lecture series by Ralph Leighton, first presented at The Douglas Robb Memorial Lectures at the University of Auckland. http://www.vega.org.uk/video/subseries/8
Johnsen, S., Lohmann, K.J., Warrant, Eric.J., 2020. Animal navigation: a noisy magnetic sense? Journal of Experimental Biology 223, jeb164921. https://doi.org/10.1242/jeb.164921