A compass works by aligning its pin with the Earth’s magnetic field and pointing North, allowing humans to navigate through unfamiliar environments. Though we know now that human compasses are not 100% accurate due to local disturbances in the Earth’s magnetic field (good thing we have GPS cellphones anyway), many animals have their own internal “compass” that helps them to navigate and determine the proper direction to travel for food, home, or migration. Such animals are able to actually sense Earth’s magnetic field and use this information for their own navigational benefit. Honey bees (Apis mellifera) in particular possess this magnetic sense, likely due a metal called magnetite that exists in their abdomens. Because of this sensitive metal, they are able to sense the directionality of the magnetic field and use this ability primarily when foraging, finding their way back to their hives, and orienting themselves within them.
The magnetic sense of animals like honey bees is difficult for researchers to understand because it is not a sense that humans possess and thus we only have a limited perception of how it works. Past experiments have shown that honey bees can sense local and subtle variations in the magnetic field, but the true underlying mechanism for this ability is still unknown. Trying to shed light on the complexity of the magnetic sense, researchers Veronika Lambinet and colleagues investigated whether honey bees are sensitive to the polarity of magnetic field, meaning they can sense where magnetic north and south are. To be polarity sensitive would give the honey bees a strong indicator of what direction they are oriented in, help them remember where to go for the best food, and then help them return to their hives. Furthermore, this ability would be in contrast to being “inclination sensitive,” in which an animal could sense the field’s intensity where they currently are relative to their destination.
To test whether honey bees are polarity sensitive, the researches set up an experiment in which they put bees in watch glasses that had a mechanically-generated magnetic field around them. They first trained each bee to associate a sugar reward with a magnetic field that converged towards the reward itself. Once the bees had developed this association, the researchers reversed the magnetic field away from the sugar reward to see if the bees would still respond to this change in polarity. If the bees responded to the magnetic field in its normal state but did not respond to the reversal, then the researchers predicted that they are in fact sensitive to polarity.
It turned out that the bees in fact did not respond to the reversal of the magnetic field, as they visited watch glasses with and without the reversed magnetic field equal amounts of time. This result means that honey bees are polarity-sensitive and can also likely detect very small changes in Earth’s magnetic field intensity and polarity. Knowing they possess this ability helps us to understand how bees can both use their magnetic sense to find food and move throughout their dark hives, as the magnetic sense does not rely on light. It is also one more piece of evidence that provides important information about how animals in general exploit Earth’s geomagnetic field to navigate. Each piece of research on this moves us closer to understanding an ability that we as humans cannot even possess without the help of outside instruments.
Lambinet, K., Hayden, M.E., Reid, C., & Gries, G. (2017). Honey bees possess a polarity‐sensitive magnetoreceptor. Journal of Comparative Physiology A 203: 1029-1036.