The Monarch (Danaus plexippus) is a common poisonous butterfly with a wingspan of 8.6 - 12.4 cm. It is bright orange with black wing veins and outer margins. The wings have white spots on outer margins, and there are three orange patches near the top of the forewings. The hindwings are rounded, and are lighter in color than the forewings. The body is black with white spots.

Male monarchs have a dark spot on the hindwing. Females don't. Males also have much thicker wing veins and small claspers at the end of the abdomen.

The monarch gets its poison (cardenolide glycosides) when it is a caterpillar, from eating the poisonous milkweed plant (genus Asclepias) while in its larval stage. The adult lays its eggs on the milkweed, and the larvae that hatch eat it.

Animals that eat a Monarch get very sick and vomit (but generally do not die). These animals remember that this brightly-colored butterfly made them very sick and will avoid all Monarchs in the future. Of course, as is nature's way, the Monarch butterfly has a mimic. The North American Viceroy butterfly (Limenitis archippus) looks almost identical to the Monarch, but is not poisonous. Its similarity to the Monarch offers it protection from predators.

Monarch butterflies really are beautiful and cool in many ways. One ability which is helpful in their travels is to use the earth's magnetic field for navigation. This comes in handy on cloudy days and their schedule still calls for some serious mileage north or south. For all practical purposes they have a little compass built in somewhere in their bodies.

Ref: J.A. Etheredge et al (1999) "Monarch butterflies ( Danaus plexippus L.) use a magnetic compass for navigation" Proceedings of the National Academy of Sciences, vol 96, no 24, pp 13845-6.

Monarch Butterflies are also know as King Billy or King Billies by Candadians (and others who are Lepidopterists) in honor of King William of Orange whose colors were orange and black.


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