Monarch Butterfly

Danaus plexippus

• Content: Bill Kaufman
• Photo(s): Bill Kaufman

A diet of milkweed makes this butterfly distasteful to predators and the orange coloration is a warning that says to other creatures, “do not eat me.”.

Everyone loves Monarchs but some mistake it for our common Queen. The Monarch is a rich cinnamon-orange color on the top with black veins and a light, yellowish-orange underside; the Queen lacks the black veins on top, and the color is a darker orange on both the top and bottom. There is less black on the forewing tip of the Queen and there are several distinct white spots on the forewing submarginal area that are absent in the Monarch.

The males of both species have a small black oval spot on either side near the abdomen along a hindwing vein. The caterpillars are similar but the Monarch has two pairs of black filaments while the Queen has three. The pupa of the Monarch is larger than that of the Queen but they are very difficult to tell apart.

Millions of Monarchs from central and eastern North America migrate to winter over in the mountain forests of central Mexico. In the spring they move north, stopping to breed where they find milkweeds, their larval food plant. Their offspring continue north and also stop to breed; by summer the next generation has spread over much of North America. Starting in late summer, what is by now the 4th or 5th generation removed from the ones that wintered in Mexico the previous year repeats the migration cycle.

Remarkably the butterflies that return to Mexico find their way even though they have never been there before. Monarchs found in Western North America also undergo this migration cycle, but they winter along the coast of California. There are some populations that do not migrate but breed year-round in southern Florida and Texas.

Milkweed is poisonous to most animals, but the Monarch (and Queen) larvae are unaffected. They are, in fact called milkweed butterflies. This diet makes them distasteful to predators and the orange coloration of the butterfly is a warning that says to other creatures, “do not eat me.” Male milkweed butterflies feed on nectar from ageratum, eupatorium and heliotrope flowers to obtain an alkaloid pheromone that attracts females.

The photographs were taken at Tohono Chul Park but Monarchs, although not nearly as common as Queens in this area, may be found all over the city, particularly in areas where the above-mentioned flowers are planted. The caterpillars in the photo are on a milkweed plant.