Some objects in nature inherently have a red coloration due to their chemical composition or biological pigments. Determining which objects are naturally red can be useful for artists looking to accurately depict the colors found in nature or for scientists studying the causes and functions of biological coloration. In this article, we will explore common examples of objects that are red by nature without artificial coloring.
Blood
Blood obtains its red color primarily from the protein hemoglobin. Hemoglobin contains iron atoms that can form bonds with oxygen, giving blood its ability to transport oxygen throughout the body. The iron in hemoglobin also gives it a distinct red color when oxygenated.
While human blood generally appears redder when oxygenated and darker red when deoxygenated, blood is inherently red regardless of oxygenation levels due to the presence of hemoglobin. Blood from all vertebrate species contains hemoglobin and is red, though the shade may vary between organisms. For example, many fish have blood that appears blue or green, but this is still caused by the red hemoglobin being visible through scales and tissue.
Red Peppers
Red bell peppers naturally obtain their vivid red color from lycopene, a carotenoid pigment. Along with tomatoes, red peppers are one of the highest natural sources of lycopene. It is a potent antioxidant that may offer health benefits.
The level of lycopene increases as peppers fully ripen, resulting in a bright red skin and flesh. Other red-pigmented fruits and vegetables rich in lycopene include watermelon, pink grapefruit, and papaya. However, red peppers stand out as having extremely high lycopene content per serving.
Ruby Gemstones
Ruby is a gem-quality variety of the mineral corundum, composed of aluminum oxide. Chromium impurities in corundum result in the deep red color of ruby. The word “ruby” originates from the Latin “ruber”, meaning red.
Natural rubies form through geological processes and are found in a limited number of locations around the world. They are considered one of the four precious gemstones, along with diamonds, emeralds, and sapphires. Synthetic rubies can also be created through manufacturing processes, but natural rubies are most valuable.
Ladybugs
Ladybugs, more accurately called ladybird beetles, contain a red pigment called coccinellin. This bright scarlet pigment is found in most of the over 5,000 species of ladybugs around the world. It serves as a warning signal to potential predators that ladybugs may not taste pleasant.
In some ladybug species, the red coloration only appears at the adult stage. Ladybug larvae and pupae may be black, gray, or yellow until they fully develop wings with the characteristic red coccinellin pigment. The distinct red and black pattern makes ladybugs easy to identify.
Cardinals
The cardinal is a medium-sized songbird found in North America named for the male’s vivid red plumage. While the female cardinal is more brownish in color, the male’s red feathers come from carotenoid pigments obtained through its diet of seeds and fruit.
Cardinals molt and replace their feathers annually. The brilliant red coloration helps male cardinals attract mates and defend their breeding territories. When kept in captivity away from their typical diet, cardinals can lose their reddish hues due to insufficient carotenoid levels.
Redwood Trees
Redwood trees refer to a few related species of massive conifers on the United States Pacific coast: the coast redwood and giant sequoia being the most common. They derive their name from their reddish-brown bark and heartwood.
The red pigmentation comes from tannins and other chemical compounds in the wood. These serve to protect the trees from insects, fungi, and other threats. Redwood bark also helps the trees retain moisture during drought conditions. The reddish bark is present throughout the redwood tree’s lifespan of over 2,000 years.
Red Foxes
While foxes exhibit a range of coat colors, the North American red fox lives up to its name with fur that is predominantly reddish-orange. The red fur is a result of pigmentation from pheomelanin, a protein involved in melanin production that also gives many mammals red hair and whiskers.
In the winter, red foxes may appear more gray as the fur in their undercoat thickens. They may also blacken with age. But typically red foxes maintain their signature red coats throughout their lifespans due to the pheomelanin pigment. The coloration provides camouflage in their environment.
Coral Reefs
Coral reefs contain several species of corals that are naturally red due to their symbiotic relationship with red algae called zooxanthellae. The algae live within the coral’s tissues, producing nutrients through photosynthesis and giving coral its vibrant coloration.
Without zooxanthellae, coral would be white. The loss of these algae results in coral bleaching, leaving reefs colorless. Other corals like soft corals and gorgonians also contain red pigments like astaxanthin to allow optimal light absorption for their algal symbionts, contributing to richly hued reefs.
Ruby-Throated Hummingbirds
Male ruby-throated hummingbirds are adorned with iridescent red feathers on their throats, giving them their name. This bright crimson patch results from the physical structure of the feathers, which refracts light to produce vivid color.
Pigment cells called melanocytes alter the anatomy of the hummingbird’s feathers, removing the tiny air pockets that create blue or green iridescence and resulting solely in red. Females may also exhibit some red on the throat but generally, have white underparts. The males’ red throats help attract females.
Cranberries
Cranberries get their red hue from anthocyanins, a subclass of flavonoids that provide pigmentation to many red, purple, and blue plants. Anthocyanins have antioxidant properties and benefit plant health.
They are found in high concentrations in cranberries, specifically anthocyanidins like cyanidin, peonidin, and petunidin. The level of anthocyanins increases as cranberries mature, deepening their scarlet color. Similar berries like lingonberries and chokeberries also contain anthocyanins and natural red hues.
Red Maple Trees
The red maple tree is named for its bright red flowers, leaf stems, and fall foliage. These red parts obtain pigmentation from a class of compounds called anthocyanins, the same antioxidant phytochemicals that give cranberries and other fruits their red-purple colors.
Red anthocyanin production in maples is influenced by light exposure, temperature shifts, and plant hormones. Red maple trees can tolerate shadier environments than other maples, as their red pigments allow more light absorption for photosynthesis in low light conditions. The red foliage stands out vibrantly in the fall.
Cherries
Sweet and sour cherries contain high levels of anthocyanins like cyanidin, particularly in their skin and flesh. This class of red and blue plant pigments gives cherries their dark red coloring as they ripen.
The anthocyanins in cherries act as antioxidants and give cherries health benefits. Sour cherries contain higher anthocyanin levels compared to sweet cherries. As cherries mature, anthocyanin concentrations increase, resulting in darker red hues. This makes fully ripened cherries deeply and naturally red.
Radishes
The common red radish gets its color from anthocyanins concentrated in its outer surface. Smaller radishes tend to be most vibrantly red. The levels of red pigment decrease as radishes grow larger.
Radishes belong to the Brassicaceae family, known for containing anti-inflammatory, cardio-protective anthocyanins. Red radishes not only have a red exterior but a deep red interior as well. The pigments serve as antioxidants and form a protective barrier against fungi and other pathogens as radishes grow.
Rhubarb Stalks
Red rhubarb varieties have vivid crimson stalks resulting from the presence of anthocyanins. Higher light exposure and cool night temperatures promote anthocyanin synthesis, creating deeply pigmented rhubarb.
The levels of red anthocyanins are higher in rhubarb stalks compared to rhubarb leaves. Rhubarb leaves contain toxic compounds and should be avoided. But the stalks are rich in beneficial anthocyanins that provide antioxidant, anti-inflammatory, and other health effects. Cooking rhubarb helps retain the red anthocyanin content.
Summary
In nature, red colorations often serve important biological purposes, like attracting pollinators, providing camouflage, or protecting against UV damage. Red hues in wildlife, plants, and geology frequently stem from pigments like carotenoids, anthocyanins, and other flavonoids with antioxidant properties. By understanding the causes of natural red coloration, we gain appreciation for the beauty and complexity of the living world. Discovering which objects are inherently red also provides inspiration for artists and insight for scientists.
