From BBC News :
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 caused by tiny structures inside the animals’ hairs, but those shapes vary across the family tree.
This suggests, the researchers say, that the striking blue is not driven by sexual selection – unlike many other bright colours in the animal kingdom.
This argument is also supported by the fact that tarantulas have poor colour vision, and do not appear to show off their hairy blue body parts during courtship. More.
The researchers think that the blue colour must be a signal to some other party.
See also: What is the true significance of convergent evolution?
and
Evolution appears to converge on goals—but in Darwinian terms, is that possible?
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