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.
The team also purchased specimens of eight tarantula species, and took a close look at those blue hairs.
They used electron microscopes to zoom in on tiny shapes within those hairs and conducted simulations of how those shapes could produce a "structural colour" by reflecting - very specifically - this wavelength of blue light.