×

Monarch Butterflies – A migrating marvel

  • the caterpillars and chrysalises that I have been raising Courtesy of Ruth Smith



For the Monitor
Saturday, September 02, 2017

In recent years the population of Monarch butterflies was so low that seeing just one of the large orange and black insects was reason to rejoice. Recently I’ve been doing a lot of rejoicing. Sightings of butterflies and caterpillars have increased this year, but Monarchs must still contend with many challenges as one of the few insects that migrate south for the winter.

Migration for any creature is arduous, but for one that is about 4 inches in size, has wings made of tiny, delicate scales, eats only nectar from flowers and travels up to 3,000 miles, it is a miracle that any of them make it. Before they head south they must endure hazards at each stage of their life, but various adaptations help them survive.

Female Monarchs lay single tiny white eggs on the underside of a milkweed leaf. The outer covering of the egg is hard and waxy, protecting the larva from drying out or from being eaten by beetles, ants and other insects.

Once the larva has hatched, the minute caterpillar has easy access to its first meal. It feeds on its host plant and will eat only milkweed leaves for its entire caterpillar stage of about 10 days. This diet may seem monotonous but it also provides protection for the caterpillar, and ultimately the butterfly. A toxin in the milkweed renders the insect poisonous to birds and other predators. Another protective feature is a pair of long pointy filaments on each end of its body. One pair are the antennae that help it feel where its food is. The other pair looks nearly identical, thus giving the appearance of a double headed creature – a confusing image for a potential predator.

The black, yellow and white caterpillar molts several times as it grows, eating its shed skin. When it is about 2 inches long, it attaches itself to the underside of a leaf or branch, and hangs upside down in a J shape. Its final molt transforms the caterpillar into a light green, camouflaged, but jewel-like chrysalis, rimmed with shining gold dots.

Over the next 10 to 14 days, the caterpillar becomes completely reorganized, disintegrating into an insect soup before reformulating into an entirely new creature. Toward the end of the transformation, the chrysalis becomes dark and then clear, revealing the compact butterfly within.

The butterfly emerges with damp, crumpled and limp wings. It hangs upside down and pumps fluid through the veins of its wings. In two hours the wings have expanded and dried and the butterfly is ready to fly. The marvelous transformation from a skinny leaf-bound caterpillar to a graceful orange and black sky-dancer is complete. However, its journey has just begun.

At this time of year, eastern populations of Monarchs make an epic migration to Mexico. Traveling between 50 to 100 miles per day, it may take up to two months to reach the Sierra Madre Mountains. During the winter, hundreds of thousands of Monarchs will congregate in roost trees, creating an orange forest even more glorious than our New Hampshire fall foliage.

The southern migrants will live up to 9 months but will not return to their birthplace in the spring.

Beginning in March they will begin to fly north. After stopping in Northern Mexico or the Southern U.S. where females will lay eggs, they will die. The resulting offspring will mature and fly further north to repeat the process. A third generation will arrive in our area by late spring or summer and create the fourth generation which will be the southbound migrants that are emerging now. Each generation is a pioneer with no experience to build on during their travels. It is truly one of the marvels of nature.

To help ensure the continuation of this cycle, some of the wintering grounds have been protected as a biosphere reserve. More people are planting or protecting milkweed for larval food and growing nectar-rich butterfly gardens for adults. These efforts will complement their adaptations and bolster the chances for success of the Monarch as it faces challenges of habitat loss, pesticides, climate change and other known and unknown obstacles.

You can see Monarchs and learn more by attending the Monarch Festival on Saturday at Petals in the Pines in Canterbury, petalsinthepines.com.

For additional information visit: monarchlab.org, fs.fed.us/wildflowers/pollinators/Monarch_Butterfly/migration or monarchwatch.org/blog/2017/07/20/monarch-population-status-31.