Royal Mimicry: Entomology Meets Etymology

By Katherine McFerrin and John McFerrin

            Summertime in North America is the breeding season for the Monarch butterfly, West Virginia’s state butterfly. Monarchs have a bold wing pattern of black borders outlining orange teardrop shaped patches and white spots dotting the edges of their wings. The northeastern U.S. is a pit stop before heading south to their overwintering grounds in southwestern Mexico. Although monarchs are best known for their arduous 3,000 mile migration, the Monarch, along with the Viceroy butterfly, is also one of nature’s best examples of mimicry.

            The mimicry even extends to their names.  The Monarch is, of course, the king or queen.  The word Viceroy has its roots in an old French term for the assistant to the king.  In the old days, when Britannia ruled the waves and England had an empire, various far flung colonies were overseen by viceroys who were in India, Ireland, North America, etc. in place of the king.  The king (or queen) was the ruler; the viceroy was there in his or her stead.  In the butterfly world, the Viceroy looks very much like the Monarch and, in appearance at least, could take its place.

            Mimicry is when a species, the mimic, resembles another species, the model, to avoid predation. In the case of the Viceroy and Monarch, this mimicry has roots in the Monarch’s ability to dissuade predators through chemical defenses and color. Monarch larvae eat milkweed plants, which contain cardiac glycosides, aka cardenolides. This makes Monarchs poisonous to predators, such as birds. To warn predators, Monarchs display aposematic coloring, specifically their bright orange color acts as a signal that the butterflies are poisonous. When a predator eats a Monarch or even part of a Monarch’s wing, the cardenolides may cause the predator to vomit or go into cardiac arrest. Over time, predators associate the warning color with the bad experience. 

Even though they don’t share the Monarchs’ chemistry, Viceroys ride their coattails, so to speak.  Although Viceroys have their own chemical defenses, appearing similar to Monarchs gives them the benefit of the Monarchs’ chemical defenses in deterring predators as well as their own. In the butterfly world, looking as if you are poison can be as good as actually being poison.  

            At a glance, Monarchs and Viceroys appear the same with bright orange shapes, black lines and white spots. There are, however, visual differences. Viceroys can be up to 1.5 inches smaller than Monarchs, and Viceroys have a distinct black line across their hind wings. A more noticeable difference is their flight patterns. Viceroys fly in a quick and erratic flapping motion that keeps them closer to the ground, whereas Monarchs appear to float with a flap-flap-glide rhythm that allows them to fly at greater heights. 

            They are also around at different times of the year.  Monarchs migrate yearly to Mexico and southern California, but Viceroys do not migrate. In the northeastern U.S., Monarchs usually arrive in mid to late June with Monarch sightings peaking in the fall as the butterflies begin to migrate south. Viceroys typically emerge by late May. 

Taken together, the physical appearances, flight patterns and seasonality of Monarchs and Viceroys can be used to distinguish the two despite their strikingly similar coloring.  You can tell which is the real king and which is there in place of the king.