Monarch butterflies have developed two main adaptations for survival: warning coloration and toxicity, explains National Geographic. As a caterpillar, monarchs eat a diet mainly of milkweed. Milkweed contains a toxin that causes discomfort in potential predators. To avoid ingesting the toxin, predators often leave the monarch caterpillar alone. The brightly colored wings of the adult monarch suggest, to potential predators, it is dangerous to eat.
The monarch butterfly is at a disadvantage when it comes to camouflage, so it uses two adaptations to survive. The first, toxicity, helps the monarch caterpillar reach adulthood. Monarch butterflies rely heavily on the milkweed plant for survival. Monarchs only lay their eggs on milkweed so that, when they hatch, the larvae can eat the plant and ingest the cardiac glycosides unique to milkweed. These glycosides are toxic to other animals and cause them to vomit if they eat the caterpillar. As a result, predators tend to avoid the monarch caterpillar and the discomfort caused by consuming it.
As an adult, the monarch butterfly remains toxic and uses warning coloration to avoid predators. Bright colors are a telltale sign of toxicity. Thus, similar to tree frogs in the rainforest, predators tend to avoid monarchs due to their flamboyant coloring. Toxicity fades as the monarch ages, but the bright colors still serve their purpose of warding off predators.