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September is monarch migration season. In 2015, monarchs came through northeast Ohio in greater numbers than they had in recent years. Their lifecycle of long-distance migration is impressive. It also provides a window into the challenges that wildlife faces to survive in a developed world.
Monarchs spend the winter in the oyamel fir forests of central Mexico. Millions crowd into colonies that cover, on average, just 15 acres. Since 1994, the highest number of recorded butterflies approached one billion (in 1996-97). Numbers dropped to 34 million in 2013-2014. Last winter, butterfly numbers rebounded to 200 million.
It takes three or four generations of monarchs to migrate from overwintering grounds to summer breeding habitat in the northern United States and Canada. Migration starts as the air warms in early March. Monarchs leave the protection of the forests, mate, and seek the nearest milkweed fields to lay their eggs. The offspring are Generation 1.
Generations 1 and 2 journey progressively north, mating, laying eggs, and dying along the way. The summer monarchs in Ohio are Generation 3. Some stay to breed and others venture across Lake Erie into Canada.
In the fall, we see Generation 4 heading south. These butterflies will make it all the way to Mexico in one generation, overwinter there, and then start the cycle again.
Northbound and southbound butterflies provide different observation opportunities. Breeding monarchs rely on milkweed, the only host plant that their caterpillars eat. When females arrive in late June, they typically lay one egg on the underside of milkweed leaves. The caterpillar eats the milkweed, internalizing the plant's toxic chemicals. To warn predators, the caterpillar soon turns a distinctive pattern of bright yellow, white, and black.
When ready, the caterpillar finds a sturdy place on its host or nearby plant where it attaches itself and forms a magnificent greenish chrysalis with gold spots. After nearly two weeks, the chrysalis becomes transparent; inside you can see the butterfly that will emerge in a day or two. With their bold orange and black pattern, monarchs are the mostly widely recognized butterfly in North America. You can tell the difference between female and male butterflies. Females have thicker black wing veins and appear darker overall than males.
Southbound monarchs can travel as many as 50 miles a day. They must replenish their energy reserves at stop-over areas. They seek old fields in the afternoon where they can feed on nectar-rich flowers, such as goldenrod and New England aster, before retreating to nearby forests in the early evening. The prairie near Brecksville Nature Center and the large meadows along the Cross Country Trail near Pine Hollow are both excellent monarch habitats.
Will we see as many monarchs as last year? Unfortunately, scientists are predicting fewer this year. Scientists attribute long-term population decline to loss of habitat. To survive, monarchs need food all along their annual route; loss of habitat in just one place can have ripple effects through the population. Scientists also find that weather can cause annual population fluctuations. In 2015, we had ideal weather conditions, contributing to the bump in butterfly numbers. This year a sleet storm in March in Mexico killed many monarchs and may have reversed the bump.
To ensure a brighter future for this amazing animal, people across North America are working together to protect monarchs and a patchwork of plant communities that support them during their four-generation journey. Cuyahoga Valley National Park is part of the Monarch Butterfly Sister Protected Area Network, an international effort by Canada, the United States, and Mexico to conserve monarchs. Monarch Watch is an organization that promotes protection by inviting everyone to plant butterfly friendly flowers in your yard.
For information about how you can create monarch habitat in your yard, visit monarchwatch.org.