Bees could carry tiny magnetic ‘compasses’

A surprisingly high number and diversity of bee species – 74 out of 96 tested – have magnetic propertiesaccording to research by my colleagues and Irecently published in the journal Science Advances.

Some animals are capable of using iron-based magnetic compounds such as magnetite detect and navigate via the Earth’s magnetic field – a sense called magnetoreception. We considered magnetism in the insects we tested as an indicator of which species might be magnetoreceptive.

For decades, biologists have known that cavity-nesting social bees exhibit magnetoreception. Most researchers have assumed that this internal compass is linked to life in a colony; bees communicate the location of floral resources to other members of the colony through a dance that indicates direction relative to the position of the Sun and the geomagnetic field.

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Our study had two objectives: to compare magnetism between bee species living in groups and those living alone, and to trace the evolutionary origin of magnetoreception in bees.

Finding magnetism everywhere we looked

To test magnetic responses, we collected bee specimens from across the Apidae family, which includes social species such as honey bees as well as solitary species such as chimney bees. We ground dried dead bees into powder, then we measured the degree of magnetism of this powder. in a magnetometer.

To our surprise, we found that the magnetic response was strong in both bees that live in groups and those that live alone. This result forced us to reject our initial hypothesis that magnetism was only necessary for social bee species.

Even more unexpected, a bee from a small social species in the family Halictidae was also strongly magnetic. We then expanded our research to include bees from across the bee evolutionary tree, suspecting that the evolutionary origin of magnetism might be found in older lineages of bees.

We identified some trends in the strength of the magnetic response of bees in our study. Larger bees have been tested to be more magnetic. Social bees tend to be more magnetic than solitary bees. And cavity-nesting bees tended to be more magnetic than ground-nesting bees.

Overall, however, we detected magnetism in all different bee families, in social and solitary bees, in nocturnal bees, and in bees that live in nests in the ground as well as those that live above ground in hives. Insects from other groups that we looked at for comparison, including beetles, wasps, and flies, were also magnetic.

We once again had to reject our hypothesis; this time, we demonstrated that magnetism probably predates the evolutionary origin of bees. We concluded that magnetism is likely an ancient and well-preserved trait.

What we still don’t know

Our work leaves many questions unanswered.

On the one hand, even if we assume that the magnetic response is an indicator of magnetoreception, it is notoriously difficult to demonstrate this because it requires experiments with living organisms removed from their natural environment.

Magnetoreception is one of the most controversial animal meanings. Although there is good evidence that some organisms have the ability to sense and navigate Earth’s magnetic fields, it is likely that not the first meaning used, even for organisms with magnetoreception. This makes it difficult to isolate yourself and study. Even among bumblebees, which, according to biologists, are magnetoreceptivethere are many left questions and doubts on their use of this meaning.

Scientists are more certain that bees are magnetoreceptive-researchers even trained them distinguish between local magnetic anomalies. We therefore assumed that the insects we tested that had stronger magnetic responses than bees are also magnetoreceptive. But we can’t prove it. Furthermore, our work does not explain the function of magnetism, nor the mechanism behind magnetoreception.

And although the strength of the magnetic signal varied across body parts, it was never limited to just one body part of the bees we tested. This means that some of the assumptions about how magnetoreception works – for example, thanks to light-sensitive cryptochromes in the eyes– are not well supported by our results.

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