The appearance of orange and black on an insect is a biological strategy known as aposematism. This high-contrast coloration acts as a warning signal to potential predators, advertising that the insect is either toxic, tastes bad, or is otherwise dangerous to eat. The bright pigments serve as a memorable visual cue, conditioning birds and other vertebrates to avoid anything displaying this distinctive pattern. Many different insects across several orders have independently evolved this color scheme, often by sequestering toxins from their host plants to make themselves unpalatable.
Butterflies and Moths: The Flyers
Among the most recognizable insects utilizing this color scheme is the Monarch butterfly, Danaus plexippus, a member of the order Lepidoptera. Its large wings are vibrant orange, overlaid with thick black veins and a black border dotted with white spots. This striking pattern directly correlates with the butterfly’s toxicity, which is acquired during its caterpillar stage.
Monarch caterpillars feed exclusively on milkweed plants, ingesting and storing the plant’s toxic cardiac glycosides, which are poisonous to most vertebrates. This sequestered toxin remains in the insect’s body throughout its transformation, making the adult butterfly distasteful and potentially nauseating to birds. The coloration is so effective that it is often mimicked by other species.
A smaller example of an orange and black flyer is the Cinnabar Moth, Tyria jacobaeae, a day-flying species. Its hindwings are a bright vermillion and black, which also signals its unpalatability. This toxicity is derived from the toxic alkaloids it consumes as a larva from its host plant, ragwort.
Beetles: Hard-Shelled Warning Signs
Beetles, belonging to the order Coleoptera, are distinguished by their hardened forewings, called elytra, which meet down the middle of the back to form a protective shell. A common orange and black beetle is the Multicolored Asian Lady Beetle, Harmonia axyridis, which, despite its name, is often a pale orange rather than the traditional red of native ladybugs. These beetles have a variable number of black spots on their elytra, but they are most reliably identified by the distinct black “M” or “W” shape on the white area behind the head, the pronotum. Like many brightly colored insects, the Asian Lady Beetle’s coloration serves as a warning, and they can secrete a foul-smelling, yellowish fluid when disturbed to discourage attack.
Another distinct example is the Colorado Potato Beetle, Leptinotarsa decemlineata, an agricultural pest. The adult beetle has a yellowish to orange-brown body with ten prominent black stripes running lengthwise down its convex, oval-shaped back. This species is an example of an insect that uses its coloration less for aposematism and more for being conspicuous.
True Bugs: Flat Bodies and Piercing Mouthparts
Insects of the order Hemiptera are known as the “true bugs,” a group defined by having mouthparts formed into an elongated, jointed, piercing-sucking tube called a proboscis. They also characteristically possess a large, triangular plate on their back, the scutellum, which is visible between the bases of their forewings. The Large Milkweed Bug, Oncopeltus fasciatus, is a prominent true bug that displays a bold orange and black pattern.
The adult Large Milkweed Bug features three distinct black patches on its orange-red body, which act as a warning signal of its unpalatability, similar to the Monarch butterfly. This species feeds on the seeds of milkweed plants, using its specialized mouthparts to suck out the juices and acquiring the same defensive cardiac glycosides that make it toxic to predators. A related, though less toxic, true bug is the Boxelder Bug, Boisea trivittata, which has a black body outlined with reddish-orange markings along the edges of its wings and the thorax. These true bugs are commonly known as nuisance pests when they congregate in large numbers on the sunny sides of buildings in the fall, seeking sheltered places to overwinter.