The City Naturalist

City Naturalist

Monarch Caterpillare and Butterfly

Article and Photos by Leslie Day

MONARCH (Danaus plexippus)

METAMORPHOSIS: Monarchs progress through four separate stages of life: the egg stage, the larval stage, the chrysalis stage, and the butterfly stage.

EGG STAGE: When the Monarch butterflies return to the North from Mexico they mate and lay their eggs on Milkweed leaves. There are stands of milkweed plants growing on the small hill just west of the running track (just North of 72nd along the Hudson in Riverside Park), and along the southern stairs winding down to the Rotunda at 79th Street. The eggs hatch in 3 to 5 days and the tiny, l/8th" long, Monarch caterpillar eats its way out of the egg, and then proceeds to eat the milkweed leaf its egg was laid on.

LARVAL STAGE: The caterpillar grows to 2" long before it pupates in a jade and emerald green chrysalis. The caterpillar is very colorful with black, white and yellow bands. It has 2 long filaments or horns that develop near its head and two more on its next-to-last abdominal segment. It has eight pairs of legs, using five of them to hold its body up when it crawls, and the three remaining pair near its head to help the caterpillar crawl. With sharp nippers in its jaws it cuts holes in leaves. It eats almost nonstop until it is too big for its skin. The catepillar sheds its old skin, eats it, and then continues to eat milkweed leaves. It molts 4 times until it is ready to change into its 3rd stage of development.

CHRYSALIS STAGE: In two to three weeks the caterpillar is 2 inches long and must find a place to enter its next stage of metamorphosis, the pupa or chrysalis stage. The caterpillar looks for a firm place, such as a log or branch, which will protect it from the wind and weather. On its lower lip is a body part called a spinneret. With this the caterpillar can spin a sticky, silky thread. When it is ready to pupate it spins a small, silky, sticky knob. It hooks its back feet into the knob and hangs with its head down in a "J" formation. It splits its larval skin for the last time upward from the head to the tail. Its new skin is soft and damp. When it dries it is hard.

The Monarch chrysalis is one of the most beautiful objects in the natural world. It is jade and emerald green with glittering gold and black dots. Inside the chrysalis miraculous changes are taking place. The animal inside is changing form a crawling insect to a butterfly capable of flying over 2,000 miles. It takes 10 days for the complete metamorphosis. By 7 days the colors of the chrysalis change and the dark orange and black of the wings begins to show. Within 10-12 days the shiny, now perfectly translucent skin of the chrysalis splits and the butterfly emerges.

BUTTERFLY STAGE: The butterfly is damp, crumpled when it emerges. It pumps liquid into the black veins of its wings to stiffen them. It is a beautiful butterfly with orange and gold and brown wings. Black veins streak its wings and white dots border the wings and cover the black, velvety head and thorax. It has two pairs of wings which are covered with dust-fine scales. The scales overlap like shingles on a roof so that it can shed rain. Its tongue has become a coiled tube. As a caterpillar it was a chewing insect. As a butterfly it is a sipping insect.

Shortly after emerging, the Monarch moves its wings up and down to dry them. It makes short flights until it is strong enough to fly a longer distance. It searches for flowers with sweet nectar, like the Butterfly Bush or Buddlea davidii which you can see directly in front of the 79th Street Marina garage. In the late summe1 and all through the fall, while it blooms, this white and purple flowering bush is covered with butterflies, including many Monarchs. This bush was named after the Reverend Adam Buddle, English Vicar and botanist (1660-1715). It originates in Central and Western China. It was introduced into Europe by the French missionary David in 1864. It grows to 15 feet with mid-green lanceolate leaves, greyish beneath and slender panicles 12-15 inches long of closely packed, fragrant, lilac and white flowers.

MIGRATION: While the monarch butterflies are in the north, during the spring and summer, as many as six generations will go through the above life cycle in Canada and the U.S. Temperature and length of daylight affect their life cycle. Butterflies that hatch in midsummer will go through the life cycle and die in 4-5 weeks. Butterflies that hatch in September will live to migrate. They drink nectar from flowers. The sugar in the nectar is turned into fat. They use this fat to give them energy on their long flight south.

Monarchs that live east of the Rocky Mountains fly to Mexico. They move in great flocks. It takes them two months to reach their winter home about 75 miles from Mexico City, high in the mountains. It was discovered by scientists in the mid-1970s, but was known to the people of Mexico for generations.

Monarch butterflies have been depicted in the artwork and crafts of the Indians since before the time of Columbus. Since the 1980s The Mexican government has made the area they migrate to into a preserve. No more tree cutting can be done where the monarchs winter. No one knows for sure why the Monarchs migrate north. Scientists think it is because they may have followed their favorite food -- the milkweed plant -- as it spread northward after the ice age.

During the winter in Mexico the butterflies feed on sweet nectar and store up energy for the long flight back north. At night they rest in trees. In late April or early May they begin their migration north, mating along the way. The females are attracted by a scent released by the males. The female lays eggs along her journey north, just one egg on each leaf. Each female lays about 300 eggs. The Monarchs summer here in the North. Each September they gather in flocks of hundreds and thousands for their long journey back to Mexico.

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