Do bulls charge at red?

Short answer

No. Cattle's eyes have only two types of color receptors; they can't tell red apart as the bright, striking color we see it as — what sends a bull charging isn't the color of the cape, it's its motion. A red cape is a tradition of the spectacle, not a requirement of the bull's perception.

The claim

The claim is a familiar one: a red cloth drives a bull wild. In English, the idiom "like a red rag to a bull" is used to mean deliberately provoking someone; many languages have similar sayings. This belief doesn't stay confined to an idiom — it circulates as everyday "knowledge": someone wearing red feels uneasy walking past a herd of cattle in the countryside, and children are told that bulls hate red.

Behind the claim is an unstated assumption: that the bull sees red the way we do, and that this color stirs up a particular rage in it. The two assumptions need to be tested separately: how does a bull actually see red, and what really triggers the charge?

Where did it come from?

The belief's most visible source is Spanish-style bullfighting. In the final stage of the show, the matador uses a small red cloth draped over a stick; this cloth is called the muleta. The audience watches the bull charge at this red cloth again and again and links two things together: red and rage. The show's visual language reinforces that link; the red fabric stands out sharply against the sand-colored arena floor.

The most common explanation for why the muleta is red is that the color hides the bull's blood and gives a strong light-dark contrast against the arena floor. That explanation is itself just a popular interpretation of the tradition; but whichever it is, it's clear the choice was made for the audience, not for the bull. The real clue lies in another part of the show: the large cape used in the earlier stages, the capote, is a fabric with one side magenta and the other side yellow or blue, and the bull charges at it with the very same fervor.

What does the evidence say?

The first piece of evidence comes from the eye. A cow's or bull's eye relies on only two types of cones for color: one most sensitive to the blue-violet range, the other to the yellow-green range. As in dogs, this arrangement largely erases the difference between red and green. To a bull, a red muleta is not easily distinguished by color from a green or brown cloth; at most it stands out by a difference in lightness and contrast. The general logic of dichromacy is covered in KE-06, and cone cells themselves are covered in BI-09.

The second piece of evidence comes from behavior. In 2007, a science entertainment show tested what bulls actually charge at, using several setups. Three mannequins waving red, white, and blue flags were placed in the arena; the bull charged the white one first, then the blue one, and the red one last. In another trial, a person dressed head to toe in red stood still while two other people ran around the arena; the bull went only for the people in motion and ignored the person in red.

This experiment isn't a controlled scientific study; it was done with a handful of animals, for a television show. But it points the same direction as both the physiological findings about the eye and the observation of the multicolored cape in bullfighting. When three independent pieces of evidence point to the same conclusion, the verdict grows stronger.

Verdict — False

Bulls don't charge at red; they charge at whatever moves fast in front of them and provokes them. The red cape is a color chosen for the audience's eye, not the bull's. The one part of the claim that holds up is that a red cloth really is used in bullfighting and the bull really does charge at it; what's false is the cause-and-effect link drawn between the two.

Example — a walk through a pasture in a red jacket

Imagine you're walking along a rural trail that passes through a pasture where cattle are grazing. You're wearing a red jacket, and before reading this lesson you would have felt uneasy. But for the animals, what matters isn't the color of your jacket, it's your behavior: running suddenly, shouting, stepping between a calf and its mother. What cattle breeders recommend isn't changing your color, it's moving calmly and predictably. The same holds for a person: a bull doesn't look at the clothing or the skin tone of someone standing still; it watches motion.

Common misconception

Summary

1. Cattle's eyes have only two types of cones; red isn't easily distinguished from green or brown for them.
2. In bullfighting the bull charges the magenta-and-yellow cape with the same fervor; in a television experiment it ignored a motionless person dressed in red.
3. Motion and provocation trigger the charge; the muleta's red is a tradition chosen for the audience.

Test yourself

1. (Easy) How many types of color cones does a bull's eye have?
2. (Easy) What is the red cloth used in the final stage of a bullfight called?
3. (Medium) What property of the cape does the bull respond to?
4. (Medium) How do the colors of the large cape (the capote) weaken the claim?
5. (Hard) Why isn't the television experiment's result a strong piece of evidence on its own, and how does it still contribute to the verdict?
6. (Hard) How would you respond to someone who says, "Bulls can't see colors at all"? How should the correct statement be phrased?

Answers

1. Two; their peak sensitivities are at about 444–455 nm and 552–555 nm ("What does the evidence say?").
2. The muleta ("Where did it come from?").
3. Its motion; the bull charges at the cloth that's whipped around fast and provokes it, not at its color ("Verdict — False").
4. The capote is magenta and yellow or blue, not red; the bull charges at it with the same fervor, which shows color isn't what's decisive ("Where did it come from?").
5. It was done with a handful of animals, not in a controlled study design, but for a show. Still, because it points the same direction as measurements of the eye's physiology and the observation of the multicolored cape in bullfighting, it supports the independent evidence ("What does the evidence say?").
6. Cattle do see color; they just can't tell red and green apart well because they have only two cone types. The correct statement: "Cattle see dichromatically and don't perceive red as a standout color" ("Common misconception").

Sources

• Jacobs, G. H., Deegan, J. F., and Neitz, J., "Photopigment basis for dichromatic color vision in cows, goats, and sheep," Visual Neuroscience 15: 581–584, 1998.
• MythBusters, "Red Rag to a Bull," season 5, Discovery Channel, 2007.
• Live Science, "Why Do Bulls Charge When They See Red?"
• Snopes, "Does the Color Red Trigger Bulls to Attack?"

Next step

BI-09 unpacks this myth's physiology: it covers the sensitivity curves of the S, M, and L cones in the human eye, night vision, and the Purkinje effect, showing what two cones leave out compared to three. KE-06 carries the same question to other animals: it compares dogs' two cone types, bees' ultraviolet vision, and birds' four cones.