Monarch Butterflies (Danaus plexippus) are unique in the insect world because of their migration habits. While there are other butterflies that migrate, the Monarch is the only one known to make a two-way migration like birds do.
There are four stages in the life of a Monarch butterfly: egg, larva (caterpillar), pupa (chrysalis) and adult. A single, very tiny egg is laid on a plant, often on the bottom of the leaf near the top of the plant. In 3-4 days it hatches into a tiny black and yellow caterpillar. Caterpillars are voracious eaters and grow rapidly; so rapidly that they go through five instars, molting each time they become too large for their skin.
After about two weeks, the caterpillar is fully grown. At that time, it searches for a safe spot and then uses a hook-covered appendage called a cremaster to create a silk pad on the underside of a branch or twig and then twists around and covers itself with more silk, creating the chrysalis. The chrysalis starts out soft and skin-like, but gradually hardens to form a protective shell. During the next 10-14 days rapid change takes place within the chrysalis. The old body parts of the caterpillar undergo a remarkable transformation (called metamorphosis) to become the body parts of the beautiful butterfly that will emerge.
When it’s time to emerge (eclose), the chrysalis thins and becomes so transparent that the wings of the butterfly can be seen. The pleats of the chrysalis expand and separate and the butterfly emerges. At first the wings appear small and crumpled, but over the next hour, hemolymph from the abdomen is pumped through the wings and they expand. This entire process is performed upside down so that the wings are able to fully expand and dry. The butterfly spends the next 2-6 weeks feeding on the nectar from flowers, lays eggs for the next generation and then dies. It’s a sadly unremarkable life for such a beauty.
There can be up to six generations of Monarchs a year. The first generation is around March 15th and then every 25-37 days new eggs are laid. The last generation is around August 15th and hatches around September 15th. The last generation doesn’t become reproductive, and is said to be in “reproductive diapause”. It is this generation that migrates to Mexico to overwinter. When the weather warms and lengthening days arrive, the Monarchs complete the physiological development they halted prior to their hibernation, become reproductive, breed and lay the eggs of the new generation. Then they start the long journey back to North America and the cycle begins anew.
Monarchs have a wingspan of 3-4” and weigh about 500 mg (about the weight of a paperclip). It’s amazing that such a small and light insect can travel between 50-100 miles a day on a journey that can be as far as 3,000 miles and take two months. It’s truly amazing that they know their way to overwintering sites even though this migrating generations has never before been to Mexico!
Eastern North American Monarchs migrate from as far away as Canada using several flyways that merge into a singly flyway in Central Texas. They usually reach Texas during October. Because there are not many nectar producing plants in Mexico, it is important that they consume enough nectar while in Texas to sustain them on their journey.
Monarchs overwinter on the same twelve mountaintop areas in Mexico’s Transvolcanic Belt from late October to late March. They roost in forests of Oyamel Fir trees. These mountaintops are two miles above sea level with temperatures ranging from 32-59°F and humidity created by cloud cover. This is an ideal microclimate for the Monarchs.
While hibernating, there are several dangers that the Monarchs face. Following winter storms in this region, the skies clear and the temperatures drop, causing heat to escape into the night sky and cooling the forest rapidly (called radiational cooling). If temperatures drop below 20° F the butterflies can freeze. Also, with over-logging in this area, the forest canopy has been reduced and their protection from rain is limited; being cold and wet can lead to death. On their return flight, there are other dangers that the Monarchs face. Late spring cold fronts, the overuse of herbicides along roadsides, and human activities that reduce milkweed and nectar sources affect the ability of the Monarchs to survive.
With all the dangers that the Monarchs face, it’s astonishing that they survive at all. Sadly, they are struggling. The spring of 2014 was a low point, with only 33 million Monarchs leaving the Oyamel Fir forests (compared to one billion in 1996). This statistic got the attention of Monarch watchers who wondered if the majestic orange and black butterflies would rebound.
Thankfully this number is up somewhat in 2017, with 45 million Monarchs leaving the Oyamel Fir forests. While this is a comforting, the Monarch population is still down 84% from 1996. And with populations this low, chance events can have a huge impact.
The good news is that you can help the Monarch by creating a Monarch Waystation. These are places that provide food, moisture and shelter to migrating Monarchs and a place can be found in just about any yard and it’s not hard: Site the Monarch Waystation in a sunny, open site that is protected from wind. Plant a variety of flowering plants in bright colors that bloom from early spring through the first frost to attract adult Monarchs, and plant Milkweed, the only source of nourishment for the caterpillars. Avoid the use of chemicals (including those marked organic) in this area. And set out shallow containers with water, mashed bananas in beer, or trays of ripe fruit such as pears and peaches to provide supplemental nourishment.
Some flowers that Monarchs love include Butterfly Bush (Buddelia davidii), Purple Coneflower (Echinacea purpurea), Gregg’s Mistflower (Eupatorium), Ox-Eye Daisy (Leucanthemum vulgare), Penta (Penta lanceoelata), Phlox (Phlox paniculata), Black-Eyed Susan (Rudbeckia hirta), all varieties of Salvia, Verbena (Verbena hortensis), Yarrow (Achillea millefolium), and Zinnia (Zinnia augustifolia). These flowers are so beautiful you’ll love and enjoy them as well.
Be a positive force in helping this beautiful butterfly! Spread the news of the plight of the Monarch to friends and family. Get involved in community activities to help the Monarch butterflies. And plant Milkweed and nectar flowers. You can make a difference! Monarch butterflies are treasures to be protected and cherished. With better stewardship, Monarchs will continue to grace the skies for us, our children and their children for many years to come.