The Forest in Fall:
The Monarch Butterfly (Danaus plexippus) is believed to be the best known butterfly in the United States. It’s also the only butterfly known to complete a two way migration from the northeastern United States down to the Sierra Madre Mountains of Mexico. Before embarking on that roughly 3,000 mile journey, the monarch must first get its wings.
There are four main stages of life for the monarch butterfly including the egg, larva (caterpillar), pupa (chrysalis), and the fully grown adult stage. Females lay eggs primarily under milkweed (Asclepias spp) leaves, making it a key plant species for monarchs. After about 4-6 days, depending on weather and temperature, these eggs will hatch into larvae commonly known as caterpillars. The black, white and yellow banded larva will increase its body mass by more than 2000 times in the 9-14 day period (see photo above by Susanne Vondrak, a Black Rock Forest staff member & neighbor). After its binge of eating everything in sight, the larva will attach itself to a smooth surface where it will begin its metamorphosis. The chrysalis starts out as a green casing that will darken over the 10-14 day stage, then turning clear just before the butterfly emerges. The butterfly will emerge from its chrysalis and flap its wings for a few hours, or until they are dry and ready for flight.
Monarchs that emerge from the chrysalis during late summer enter a state of suspended reproductive development which is called diapause. Diapause and many other natural processes are controlled by photoperiod or the length of daylight in a day. These butterflies will travel about 50 miles per day, following waterways and coastlines on their trip to Mexico. These butterflies travel during daylight and can be seen roosting in large groups along branches at dusk and dawn. A series of different migration paths converge in the state of Texas where the monarchs begin the last leg of their journey. The butterflies then arrive in the same mountain ranges as many generations before them to spend their winter months in a more ideal microclimate. It is not uncommon to find several thousand butterflies on a single tree during the winter months when they huddle together to remain warm.
As the days get longer and temperatures begin to rise in the Sierra Madre Mountains, the monarchs become reproductive and lay the eggs of new generations to come. These new eggs will start the life cycle all over again, ultimately beginning the journey back to the Hudson Valley.