Erythrism

Lore & Background

Erythrism in katydids has been occasionally observed. The coloring might be a camouflage that helps some members of the species survive on red plants. There is also consensus that the erythristic mutation is actually a dominant trait among katydid species, albeit a disadvantageous one, due to the overwhelmingly green coloration of most foliage. Hence, most pink or otherwise vividly colored katydids do not survive to adulthood, and this observation explains their rarity.

Reader's Guide

Erythrism is a rare pigmentation condition that has been documented across diverse animal groups, including insects, mammals, and birds. In katydids, the pink coloration is thought to be a dominant but disadvantageous mutation, as most foliage is green, making pink individuals more vulnerable to predators and rarely surviving to adulthood. Among leopards, erythrism is rare; one study reported that two of twenty-eight leopards seen in camera traps in a South African nature reserve were erythristic, and the authors found records of five other 'strawberry' leopards from the region. In birds, common guillemots lay eggs with highly variable colors, including rare red eggs, estimated at a frequency of 1 in 1,000 to 1 in 10,000 eggs. The red color is thought to be due to the absence of biliverdin and/or an excess of protoporphyrin IX. One such rare red common guillemot egg was the Metland Egg. The condition highlights the interplay between genetics, diet, and environmental pressures in shaping animal coloration.

Did You Know?

• Erythrism in bees can be caused by feeding on artificial food coloring.
• The erythristic mutation in katydids is considered a dominant but disadvantageous trait.
• Two of twenty-eight leopards in a South African nature reserve were erythristic, with five other 'strawberry' leopards recorded from the region.
• Rare red common guillemot eggs occur at an estimated frequency of 1 in 1,000 to 1 in 10,000 eggs.

What Erythrism Is and What Causes It

Erythrism, also called erythrochroism, describes a striking reddish discoloration that can appear in an animal's hair, skin, feathers, or even eggshells. Rather than being a single condition, it is an umbrella term for any unusual shift toward red tones in an organism's natural coloration. The phenomenon can arise through at least two distinct pathways. The first is genetic: a mutation may eliminate a pigment that would normally be present, or it may drive the overproduction of a different pigment, and either mechanism can push the visible color toward the red end of the spectrum. The second pathway is dietary. A well-known example involves honeybees that took in "bright red corn syrup" left over from maraschino cherry production, which tinted their bodies an unexpected reddish hue. In both cases the underlying principle is the same—something alters the balance of pigments, and the result is an animal that looks markedly different from its peers.

Erythrism in Katydids: Camouflage and Survival Cost

Among insects, erythrism is most frequently documented in katydids, where pink or vividly colored individuals have been spotted on occasion. Researchers have proposed that in certain environments this unusual coloring could actually serve as effective camouflage, allowing a red-toned katydid to blend in among red-flowering or red-leafed plants. However, the broader ecological picture tells a different story. There is scientific consensus that the erythristic mutation in katydid species behaves as a dominant trait, meaning it can be passed to offspring with relative ease. Paradoxically, this same dominance makes the trait a significant survival disadvantage. Because the overwhelming majority of foliage in natural habitats is green, a pink or brightly colored katydid stands out conspicuously against its background, making it far more vulnerable to predators. As a result, most erythristic katydids never reach adulthood, and this selective pressure is what accounts for how rarely such individuals are encountered in the wild.

Strawberry Leopards of South Africa

Large predators offer a particularly dramatic window into erythrism, and leopards provide one of the most remarkable examples. While the condition is exceedingly rare in this species, a camera-trap study conducted in a South African nature reserve documented two erythristic leopards out of twenty-eight individuals photographed over the observation period. The researchers did not stop at their own data; they also compiled historical records from the same region and identified five additional "strawberry" leopards that had been observed previously. Together, these seven documented cases paint a picture of a small but persistent sub-population carrying the reddish pigmentation variant. The term "strawberry leopard" has entered informal wildlife discourse to describe these animals, whose coat takes on a warm, reddish-brown tone rather than the typical rosette-patterned tawny coloration. The South African reserve thus stands as a notable site where this otherwise vanishingly rare coloration has been repeatedly confirmed, offering researchers a small but valuable population in which to study the genetic and ecological dimensions of erythrism in a large felid.

Red Eggs of the Common Guillemot

Erythrism is not limited to the bodies of animals; it can also manifest in the shells they produce. Common guillemots, a seabird species, are known for laying eggs whose colors vary enormously from one clutch to the next, and within that spectrum sits a rare subset of eggs that appear distinctly red. Ornithologist Tim Birkhead has estimated that such red eggs occur at a frequency somewhere between one in a thousand and one in ten thousand guillemot eggs, making them a genuine rarity even within a species already noted for egg-color diversity. The biochemical explanation points to a disruption in the normal pigment pathway: the red hue is believed to result from the absence of biliverdin, the pigment responsible for the typical blue-green eggshell color, and/or from an overabundance of protoporphyrin IX, a compound that imparts reddish tones. One particularly notable specimen, known as the Metland Egg, has become a reference point in discussions of this phenomenon, illustrating how a single egg can carry a pigment signature that deviates sharply from the norm of its species.