Monarch
| Scientific Name | Danaus plexippus |
| Survival Strategy | Long-distant Migrant |
| Arrival in Upper Midwest | May |
| Departure | September |
| Destination | Central Mexico |
| Conservation Status | Critically Imperiled |
Spring
In mid-March, the super-generation born in the north seven months ago begins the return trip from Mexico into the southern U.S. These “super” butterflies will lay eggs and die. In May, the first generation born in the southern U.S. will migrate farther north, lay eggs, and die. These are the first Monarch to reach the upper Midwest.
Summer
The second and third generations will visit milkweed and reproduce in the Midwest from June through July.
Fall
In September, the fourth or fifth-generation (super-generation) born in the Midwest migrate to Mexico.
Winter
The super-generation will spend the winter roosting in forests in the Sierra Madre Mountains in Michoacán. In February, the northward migration begins again.
Behavior
Basking
When temperatures are cool, butterflies often rest with their wings open and facing the sun.
Puddling
Monarchs will take in needed minerals from fresh feces, urine-soaked soils, or muddy puddles like other butterflies.
Mating
Monarchs reproduce by joining the tips of their abdomens while sitting on plants or in flight.
Physiology
Metamorphosis
The larvae (also called caterpillars) will emerge from the eggs in about 3 to 4 days. The larvae will undergo five instars during the next two weeks (separated by molts). After the 5th instar, the larvae pupate (forms a chrysalis). About two weeks later, the pupae emerge as an adult monarch butterfly.
Super Generation
The birth of the super-generation is triggered by decreasing day length and cooler temperatures. These monarchs are larger, stronger, and produce very little Juvenile Hormone, which delays puberty (and reproduction) until mid-February.
Navigating by Algorithm
The DNA of a migrating monarch does not hold genetic memory and is not a map. It’s more of an algorithm that uses changing environmental conditions as inputs (climate, biota, geography) to direct migration using physiological and behavioral responses.
Navigational Sensors
To build a sense of time, monarchs’ eyes monitor the sun’s position, and their antennae are sensitive to light and earth’s magnetic field (magnetoreception). Knowing the time and the sun’s position allows this long-distance traveler to orient to the correct direction. When researchers painted monarch antennas black, the insects got lost, but butterflies whose antennas were coated with clear paint had no trouble navigating.
Seasonal Clock
The circannual clock in their brain keeps track of annual cycles, such as when it’s time to begin their journey north.
Diet
Monarch larvae (caterpillars) feed exclusively on plants in the milkweed family (Asclepias spp.). The white latex sap that milkweed produces contains a bitter-tasting mild poison. The growing larvae accumulate enough toxins, called cardenolides, to make them toxic to most potential predators. Unfortunately for the monarchs, this glue-like sap engulfs and kills thirty percent of newly-hatched larvae.
As adults, monarchs feed on the nectar of many flowering plants, including butterfly weed, common milkweed, black-eyed Susan, rough blazing star, New England aster, and Joe-Pye weed.
Lifespan and Mortality
Fewer than one out of every ten monarch eggs will survive to become an adult butterfly. Adult monarch butterflies typically live from 2 to 6 weeks, except for the last generation of the summer (super-generation), which can live up to 8 to 9 months.
Predators
Ants, spiders, flies, assassin bugs, wasps, and birds feed on monarch larvae. Adult monarchs are preyed on by birds and large orb weaver spiders.
Ophryocystis elektroscirrha (O.E.) is a protozoan parasite that weakens monarchs. Infected adults spread O.E. spores onto milkweed leaves, passing the parasite on to the hungry larvae
Climate Vulnerability
Abnormal weather patterns associated with a warmer climate can impact monarch populations. Sudden cold snaps in their winter range and extended drought conditions in the breeding grounds can contribute to population decline.
Monarchs have several traits that may make it easier for them to adapt to climate change. These traits include a geographic range covering a large area, 4 or 5 generations per year, and a high reproductive rate.
Never stop learning
Traditions linked to Monarch Butterflies:
The Purépecha Indians of Michoacán call monarchs the Parákata, or “harvester butterflies,” because their return coincides with the corn harvest.
The Mexican holiday el Día de los Muertos (Day of the Dead) occurs when the monarchs arrive in the fall. According to traditional beliefs, the monarchs are the souls of ancestors who are returning to Earth for their annual visit.
References