Monarch Butterflies
July 29,2001

It has been a good summer for butterflies. Presently a new brood of monarchs are flitting seemingly aimlessly from one gaudy blossom to another.

Although a sizable butterfly by north American standards, it weighs less than a gram. Yet these lightweights congregate in such dense multitudes that they bow the branches of the trees they rest on. The story has filled volumes and numerous web sites are available.

Countless numbers of school children have participated in the raising of monarchs from egg, to caterpillar to chrysalis to adult and are told that the ethereal creature they release may fly 2,000 miles or so to an over wintering site in Mexico. What information or lack of information keeps scientists and amateurs alike, studying the ways of monarch butterflies?

Among the 165,000 or so known species in the insect order Lepidoptera, which includes both butterflies and moths, there isn't another species that attempts such an extensive journey from north to south each autumn, and a return journey of a different generation in the spring.

A recent book, "Four Wings and a Prayer" with the sub-title "Caught in the Mystery of the Monarch Butterfly" Sue Halpern discusses the facts and mystery of monarchs and the scientists and devoted amateurs that are still searching for all the answers.

What are some of the questions? One of the early ones was, where do monarchs go in the winter? Tagging studies had shown that they did migrate. A known fact monarchs never fly at night. They can't. Once the temperature falls below 55 degrees, they become sluggish, and are unable to flap their wings. Early in the morning, until the sun warms the air a monarch butterfly is practically paralyzed. So, every autumn as the air cools, monarchs do what no other butterfly does...they migrate south for incredibly long distances, at an average of 44 miles a day, out in the open, under sunny skies and very little wind.

Questions: How do the butterflies know when it is time to leave their summer breeding grounds for their over wintering site thousands of miles away? How do the millions of monarchs from the eastern United States and Canada end up every year in a remote 50 acre site in Mexico? As no single butterfly ever makes a round trip, how do they find their way? Sue Halpren reviews and interviews those who have made extensive studies throughout the years.

It has been found that monarchs from an August brood fly south, spend the winter in great congregations in a limited space, fly north in the spring, the female laying eggs en route and dying, the next generation carrying on and heading to patches of milkweed ever further north, whence several generations later a late brood will head south again.

Monarchs have problems. In Canada, the necessary food plant, the milkweed, has been declared a noxious weed. Over wintering sites in Mexico are threatened by loggers. Pesticides, disruptive tourism and expanding human populations are some factors that have caused concern that has resulted in tri-national agreements for conservation of the monarch butterfly.