Tarantulas have evolved almost exactly the same shade of vibrant blue at least eight separate times.
That is the conclusion of a study by US biologists, exploring how the colour is created in different tarantula species.
The hue is created by tiny structures inside the animals' hairs, but those shapes vary across the family tree.
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What is more, all these blue spiders evolved almost precisely the same shade; the wavelengths the team saw in the images all fell within a tight 20 nanometre range, clustered around 450nm - a bright, cobalt blue.
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The results, again, pointed to the colour cropping up multiple times independently: several different types of shape could be seen, even on the same branch of the family tree.
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Given their relatively simple eyes, it is doubtful that tarantulas can distinguish this shade of blue from any other colour.
That is one of the reasons that sexual selection seems unlikely
