5 Amazingly Blue Animals

By Anne Casselman

Some animals are blue to attract mates, to blend in, to announce a sex change, or simply because of a fluke of nature.

No matter the reason, these cobalt creatures are hypnotizing to the extreme. (Also see “Photos: Hot-Pink Slug And 5 Other Rosy Animals.”)

Blue-Footed Booby

Some people may go blue in the face trying to woo their love, but blue-footed boobies of Central and South America go blue in the feet. (Watch a video of blue-footed boobies in the wild.)

A photo of a blue footed booby.
A blue-footed booby performs a courtship display on Ecuador’s North Seymour Island in 2008. Photograph by Wolfgang Kaehler, Corbis

The bluer the feet on this comical-looking seabird—its name is believed to have derived from bobo, meaning clown in Spanish—the better its chances at courtship, according to a 2006 study in the journal Oecologia.

That’s because the blue pigment in the males’ feet comes from the fresh fish they feed on, and is a direct and honest measure of their fitness. The bluer the feet, the healthier the bird—and the more fetching he is to females boobies looking for a good brood-daddy.

Moor Frog 

The males of this reddish-brown frog species, found in Europe and Asia, turn a distinct shade of baby-making blue for a couple of days during their fast-and-furious breeding season. (Read “New Frog Found—Has ‘Striking’ Color Change.”)

Moor frogs mate  in Germany’s Middle Elbe Biosphere Reserve. Photograph by Kevin Prönnecke, imagebroker/Corbis

Why is another question: Some experiments suggest that the female frogs don’t care whether the males are blue.

So one theory is that the male frogs evolved to be temporarily blue so that they could quickly sort through the genders in a rapid-fire way and not waste any time accidentally (and fruitlessly) trying to mate with other males.

That way they can instead focus their energy on “scrambling for females,” as the research scientists so delicately put it in a 2012 study in Behavioral Ecology and Sociobiology. Talk about speed dating!

Eastern Blue Groper

For several species of hermaphrodite fish, blue really does means it’s a boy. Take the eastern blue groper of Australia: As females morph into males, they turn a distinct shade of blue.

In fact, these fish will morph through three colors in their lives. All eastern blue gropers start out as green females. Then as they sexually mature, they turn brown. As the eastern blue gropers grow older and larger, lo and behold they transform into a large and very blue male. (See “Pictures: Fish Light Up in Neon Colors.”)

Although sometimes the color change precedes the sex change and vice versa, one thing is clear about this color-meets-gender morph—concentrations of a blue pigment called biliverdin in their blood are culprit, according to a 2012 study in the Journal of Zoology.

Blue Lobster

The odds are slim indeed—one in two million—but thanks to a rare genetic mutation, the normally grayish-green American lobster does come in blue too. (Related: “Odd-Colored Lobsters Decoded.”)

A photo of a blue lobster
A blue lobster found off the coast of Scotland. Photograph by Natural History Museum / Rex Features

But that’s not all. In the lottery of strange-colored lobsters, blue are actually not the rarest. Turns out that mutations can render lobsters all sorts of different colors. Traffic-cone-orange lobsters are one in 30 million, albino lobsters are one in 100 million, and red lobsters (which are red before they’re cooked) are one in 10 million.

Blue-Gray Taildropper Slug

This slimy and endangered native of the Pacific Northwest—one of the mascots of the Ugly Animal Preservation Society—has a remarkable escape tactic in the face of predation: It loses its tail.

No one knows what makes these slugs blue, but recent studies report that the blue-gray taildropper is a fungus eater, and spreads the spores of underground truffle species across the forest floor, according to the U.S. Bureau of Land Management.

Tell us: What other blue animals have you seen?

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