Queen Mary scientists prove sweat bees change colour
In a study published in Biology Letters, scientists led by Dr Madeleine Ostwald of Queen Mary University of London, have found that moisture in the air can cause some bees to change colour and back again when conditions dry out.
Sweat bees are known for their bright, metallic green and blue colour. Until now, reports on their ability to change colour like a chameleon have been anecdotal. This research now provides the first experimental proof.
The Queen Mary scientists studied museum specimens of a sweat bee species from North America, Agapostemon subtilior. They discovered that, when the bees were placed dry air, they appeared to be a deep blue. But as humidity increased, they turned into a “warmer, copper-green colour,” before returning to blue when conditions dried out.
Unlike most animals which get their colour from pigments, the bees have microscopic structures on their bodies that reflect and scatter light at particular wavelengths. This is the same effect that causes the iridescent feathers in hummingbirds and the changing skin colours of cuttlefish. For some animals, the structures swell slightly when exposed to moisture, causing them to reflect redder colours. The scientists at Queen Mary believe the same could be occurring with the bees but more work will be needed to “fully understand the mechanism.”
The team also looked at colour changes in the wild, analysing hundreds of public photos from the citizen science app iNaturalist, and compared these with local humidity levels. They found that, like their test results, the bees found in drier areas tended to be bluer. Moreover, they found that older animals showed the strongest colour changes, suggesting that the outer shells slowly degrade over time and allowing moisture to enter more easily.
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