Tarantula Species Independently Evolved Same Blue Hue
Researchers marvel at the evolutionary convergence, even as they're not sure what purpose the color serves.
Some tarantulas have a characteristic that might be able to charm even the most dedicated arachnophobe: they're blue. A striking, shimmering blue. And now scientists have learned that many species of the spider have evolved the same blue hue independently -- at least eight different times.
The findings come from a study just been published in the journal Science Adventures by researchers from The University of Akron (UA) and the Scripps Institution of Oceanography at the University of California, San Diego.
The tarantulas create the blue look not from pigment but from nanostructures in their hairs.
And while other animals, such as birds and butterflies, also use such tiny structures to create the kinds of colors that will impress females, sexual selection doesn't seem to be the reason tarantulas evoloved the blue.
"Tarantulas don't see well, so their blue colors could not have evolved for courtship," said the study's lead author, UA biomimicry fellow Bor-Kai (Bill) Hsiung, in a statement.
What's more, the blue shade in the tarantula species is close to the same in all of them, and yet it's created with structures that aren't the same for each species.
"Even more remarkably," said Hsiung said, "different types of nanostructures all evolved to produce the same 'blue' across distant branches of the tarantula family tree. In other words, natural selection has led to convergent evolution."
One nagging question that persists, and is yet unanswered, is "why?" What evolutionary edge do the spiders get out of being blue, if not for mating? Is the striking coloration meant, for example, to scare away potential predators?
"For them to be this specific, it means that the blue color must itself have some function," Hsiung told The Atlantic. "We definitely think it has to have some kind of visual function."
For now, though, the scientists just can't be sure.
Meanwhile, increasing our knowledge about the nanostructures could be well worth the effort, Hsiung notes. Especially if the mechanisms could be reproduced.
"They could be used as pigment replacements in materials," the researcher said. "Such as plastics, metal, textiles and paper, and for producing color for wide-angle viewing systems in phones, televisions and other optical devices."
A greenbottle blue tarantula (
You almost feel for them, spiders. They can't help being what they are, and yet almost no one is happy to see them. Especially true when they have exceedingly long legs, thick bodies and a general mien that makes you turn quickly in some other direction. Photos don't bite, though, so let's take a look at some honking-big spiders -- with Halloween on the way, we may as well get started freaking ourselves out. Shown here is the Brazilian wandering spider (a.k.a.
), a feisty and venomous crawler from South America. Just four years ago it took home an award from the Guinness World Record people for the title of "most venomous" spider. This spidey's legs can span nearly 6 inches, its body just shy of 2 inches. It gets its name thanks to its preference for strolling along the tropic floor at night seeking out prey, rather than building webs or hiding out someplace waiting to strike. During the day, it lays low wherever it's convenient -- even inside banana plants, which is how it get its nickname "banana spider."
Not to be outdone is a spider that's been making a big splash of late, with an entomologist's
blog about his encounter with one
. It's called the Goliath bird-eater (a.k.a.,
). It can weigh in at almost 6 ounces and it's been known to reach nearly a foot in leg-span. The "bird eater" moniker must be there to warn birds away, though, because this spider doesn't typically eat birds as a matter of, er, course. It will regularly eat small land animals such as frogs, lizards, and snakes, however.
Meet the golden-silk orb weaver spider. Step into its parlor, if you must. Don't be fooled by its deceptively gentle-sounding name. The female golden-silk orb weaver's body alone can reach 2 inches, its legs can stretch to more than 5 inches, and it's even been observed killing and eating tree snakes. What's more, a study published earlier this year found that these spiders, when living in urban areas,
than usual. Interesting side-note: The golden-silk orb weaver also belongs to the oldest surviving genus of spiders,
, which has a fossil in the record that dates to 165 million years ago.
The Brazilian salmon pink bird-eating tarantula has a leg-span that can reach 11 inches and weight that can tip the scales (well, for a spider) at about 3.5 ounces. Despite its name, it's not confirmed that they actually eat birds any more than do the Goliath bird-eaters. Instead, they dine on insects or the random small amphibian or reptile. Instead of making a web, it takes its prey by quick-strike ambush in the open.
The giant huntsman spider is so big it even took the trouble to have a size descriptor built into its name (given that Goliath was taken). The huntsman is neck and neck, or leg and leg, with the Goliath bird-eater for the title of biggest spider, by leg-span (in sheer body mass, though, the Goliath is more like an offensive lineman, while this spider is a lanky cornerback). A giant huntsman's legs can stretch out to 12 inches, and its speedy, crab-like gait makes it a fast hunter that excels at chasing down its meals. It hails from caves in Laos.