Monarch butterflies are a common summer sight in the northeastern United States. In late summer and early autumn country fields of goldenrod and other wildflowers come alive with the black and orange flutterers, drifting and diving among the flora. Amazingly, these swift and sensitive aerial acrobats’ flight speeds have been measured at up to 30 miles per hour.
They are also highly perceptive and super-aware.Caterpillars and butterflies can sense touch, taste, smell, sound, and light. Butterflies use their senses of sight, touch, hearing, smell, and taste to survive in the world, find food and mates, lay eggs in an appropriate place, migrate, and avoid hungry predators.
Setae (sensory hairs) on the butterfly’s entire body (including the antennae) can feel the environment. They also give the insect information about the wind while it is flying.
MIGRATION
In the autumn, avid butterfly watchers in the northeast can observe streams of monarchs moving in a southwesterly direction – migrating down to Central Mexico, to the Oyamel Forests. It is known that the monarchs east of the Great Lakes fly southwest, and in areas west of the Great Lakes, fly south-southwest, but their exact migratory path is still being plotted.
What is it that guides the monarchs and signals to them the appropriate time to begin their migration? Apparently, what the monarch butterflies sense is the changing amount of light present and the variability of day and nighttime temperatures. With the change of seasons comes the inevitable shortening of the days, longer nights, and also colder nighttime temperatures. When these characteristics show up, the monarchs leave for their over-wintering sites as much as thousands of miles away. It is thought that they either follow celestial cues such as the position of the sun, or the pull of the earth’s magnetic field to find their way to their over-wintering sites, but this is still being studied.
One recent study has found that the insects' antennae play a very important role in guiding the butterflies to their winter destination.
OVER-WINTERING
Unfortunately, the monarchs are becoming more and more vulnerable in their over-wintering sites in the high-altitude fir forests of the Transvolcanic Range of Mexico; only two of the eleven known roosting sites are well protected from logging. Continued development may mean that a winter may soon come when the monarchs no longer have a place to rest.
Once the butterflies reach their roosting site, they cluster in large numbers in the branches and trunks of the trees. While clustering they stay relatively still and maintain low metabolic rates. In mid-February, the monarchs at the roost sites become more active and mating behavior begins. By the end of February, some of the monarchs begin moving northward, and by mid-March the roost is usually depleted.
Forty to sixty percent of the monarchs die during their stay in Mexico. During the spring migration, the monarch butterflies return to their homes in Canada and the northern most parts of the United States. Along the way, they roost and reproduce, giving rise to new butterflies that will continue the spring flight back.
In Australia and New Zealand the Monarch is known as the Wanderer Butterfly. It is now believed that the butterfly has evolved to follow the pattern of the growth of its larvae's food source: milkweed.
LOSS OF HABITAT
The availability of milkweed, the host plant of the monarch, has also become a serious concern. In Canada, milkweed has been declared a noxious weed. This means that the plant is considered illegal and cannot be allowed to grow on private or public lands in Canada. Although not labeled noxious in the United States, farmers consider the plant a nuisance to crops and often use herbicides to control it along with other weeds. More and more roadsides are being planted in grass instead of being allowed to overgrow with wildflowers and weeds. The result is that butterflies have fewer places in the wild to find nectar and lay their eggs. The place the monarchs once knew to be a land full of milkweed and nectar is changing, and now offers them an uncertain future, at best.
No one really knows for sure what next year's migration will bring. Will the monarchs find the winter sanctuary they seek and will they return again, next spring? Will competition with the growing human population ultimately force them into extinction? Without milkweed, the butterflies will have lost their prime food source and sole breeding ground for future generations. Can they adapt and change along with the changing environment? It’s difficult to predict what will happen, but the current course doesn’t look too promising for the wayward wanderers. Only time will tell.
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