Shades of Prey: Can Color-blind Predators See Warning Colors?

Shades of Prey: Can Color-blind Predators See Warning Colors?
Snakes, butterflies, and more have evolved vibrant patterns to advertise their toxicity to predators.

That’s the gist behind Saturday’s Weird Animal Question of the Week from TJ Skelton, who asks via Facebook: “Can a color-blind animal still tell if another animal is [venomous], even if they can’t see the bright colors?”

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 andlions, 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. (See "Belly Up: Why Do Some Snakes Have Elaborate Belly Patterns?")

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, 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. (Also see "Why Do Butterflies Have Such Vibrant Colors and Patterns?")

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.

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.

True Colors

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. (See "Photos: Masters of Disguise—Amazing Insect Camouflage.")

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 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 "Butterflies Can Evolve New Colors Amazingly Fast.")