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Monarch Butterfly and Common Milkweed Notecard



Common Milkweed (Asclepius syriaca) and Monarch Butterfly (Danaus plexippus)

This milkweed is common in dry fields, thickets and roadsides from New England to Georgia and west to Kansas. Many insects come to feed on nectar from the fragrant blossoms; bees, wasps, flies, beetles and butterflies. The flowers are slippery and as an insect struggles for a holding place, its feet may get caught in fine little clefts at the base of each flower. If so, the insect can not escape without taking along a pair of flattened, yellow pollen masses, or pollinia, which have become ingeniously clipped to its legs. When the insect flies to another milkweed flower, the pollinia may come in contact with a receptive stigma, to which it firmly adheres. Then the insect must break the connecting bonds of the pollinia to free itself; smaller insects may actually become entrapped.

Butterflies are probably the most effective milkweed pollinators. Female monarch butterflies normally deposit their tiny eggs on the underside of milkweed leaves. The emerging caterpillars feed on the leaves, even though they contain alkaloids, distasteful compounds which, along with similar compounds, form the plant world’s main line of defense against insects and other herbivores. Monarchs have evolved an immunity to milkweed’s toxic effects; in fact they concentrate the alkaloids in their body tissues, becoming distasteful to birds and other predators. The monarch’s bright warning color discourages potential predators from attempting an unpalatable meal.

Monarchs occur throughout the U.S. and much of the world, wherever milkweeds grow. Monarchs are well known as one of the few migratory butterflies. The last generation of the summer heads leisurely southward, often congregating with other monarchs in large bands and stopping in the same rest spots each year. Butterflies that return to the north in the summer are not the same individuals that left the preceding fall, but are offspring of individuals that reproduced in the wintering grounds or en route northwards.

artwork by Lynn Usack © 1995

text by Steve Sierigk