Humans have good color vision, and some animals, like jumping spiders, can see even more hues than we can. But other predators, such as some types of sharks and lions, which may not rely as much on color, have evolved to be color-blind.
Monarch butterflies, poison dart frogs, and coral snakes are examples of toxic animals that sport warning colors, hues that would-be predators quickly learn and remember to avoid.
The blue and yellow poison dart frog (pictured at the Sunset Zoo in Kansas) advertises its toxicity through its colors. [Photograph by Joel Sartore, National Geographic Creative]
Some mammals that have no venom, such as like skunks and honey badgers, have striking black-and-white stripes that communicate to predators they might be in for a nasty fight or a noxious spraying.
Such warning colors “often vary, [but] what appears to be key is the contrasting dark—usually black or dark brown—and either yellow, orange, red, or white patterning,” like the monarch butterfly, Robert Espinoza, a biologist at California State University, Northridge, says via email.
That means whether a color-blind predator can see the specific colors may not matter in some cases: The high contrast of the prey animal's dark and light patterns “are so striking that they evoke an innate response—'Warning! Bad tasting or dangerous critter ahead,'" Espinoza says.
Let There Be Light
There's science backing this up in praying mantises or mantids, which are thought to have little or no color vision.
Luckily, “praying mantids are darn good at seeing movement and reacting quickly to it, as any fly could attest,” says Katy Prudic, an entomologist at the University of Arizona.
Praying mantises (pictured, a Tenodera aridifolia eating a honeybee) can't see colors. [Photograph by Daniel BorzynskiI, Alamy]
In a 2007 study published in Behavioral Ecology, Prudic tested how color-blind Chinese mantids would react to bitter-tasting milkweed bugs painted with gray paint of different contrasts and set against a gray background.
The mantids learned to avoid the high-contrast bugs more quickly and retained that aversion longer than they did with low-contrast bugs.
This showed that the color-blind predator could still detect a difference in color via something called luminance contrast, or “the amount of light reflected off the prey,” Prudic says.
In some ways, the cotton harlequin bug of Australia seems to have the best of both worlds: Warning colors and camouflage, which each serve to dissuade a different predator.
The insects come in two types of warning colors: solid orange and orange with iridescent turquoise patches. Birds can see these colors and know to avoid the bugs.
Mantids don't mind the warning colors, and will eat the bugs—but only the shinier turquoise individuals. The uniformly orange ones are completely camouflaged to mantis eyes, according to a 2014 study.
It’s plausible, the study says, that mantids could even influence the evolution of harlequin bugs—by eating so many turquoise insects, more orange insects could be left to breed.
See? You have to know your audience. Or they might eat you.