Monarch Migration is Underway
by Ro Wauer
Monarch butterfly fall migration is well underway. These marvelous creatures are heading south toward their wintering grounds in the forested highlands of central Mexico. I am daily finding several individuals in my yard, nectaring on various flowering plants or soaring overhead, constantly moving toward their goal another 850-plus miles away. Some of these same individuals may have started their southward trek as far away as Canada, although others may have emerged from a chrysalis much closer, some even perhaps in North Texas. But all are heading south in what is one of nature’s most amazing happenings!
Monarch migration occurs throughout Texas, but the majority passes through the state in two principal flyways. The central Texas route stretches for about 200 miles from Wichita Falls to Eagle Pass, and a second flyway exists along the Gulf Coast. The southbound migrants pass through Texas during September and October, but by the third week of October they have almost all passed through into Mexico. Although Texas migrants may originate throughout much of northern and eastern North America, their journeys end in a ten-acre area in central Mexico where five to six million monarchs over winter together, hanging from conifer boughs in huge clusters.
Monarchs are the only true butterfly migrant, the only species that travels both south and north. Although several other butterfly species, such as the painted and American ladies, red admiral, and several of the large sulphurs, are often considered fall migrants, they rarely live long enough to head back north in spring. They one-way movement is properly called emigration. Monarchs that migrate to Mexico and return to the southern United States live at least eight months, although the spring and summer generations live only four to six weeks. Those that return to Texas in spring, usually in March and April, reproduce as soon as possible and the next generation continues the northward movement. Monarchs breed four to five times per year, and almost every generation is part of the migratory movement.
Monarchs are the poster-child of the insect world. As the best known North American butterfly, monarchs attract an amazing amount on interest throughout the United States. And in spring and fall, when they are in the process of migrating, "Monarch Watch" reporters keep track of their progress and post it on the internet. "Real-time Migration Maps" can be seen at http://www.learner.org/jnorth/monarch/index.html. These are updated weekly. Anyone interested in submitting reports can do so; instructions are available at: http://www.learner.org/egi-bin/jnorth/jn-sightings. And Jim Lovett of Monarch Watch (http://www.MonarchWatch.org) reports that, in spite of earlier predictions of severely declining populations, the fall 2005 migration looks promising.
Monarch migration truly is amazing! Although we are familiar with bird migration, especially those that fly northward from southern Mexico or further south to nest in the United States. But birds are warm-blooded vertebrates, while monarchs are cold-blooded invertebrates, very different creatures, biologically and physiologically. Their survival itself is miraculous! An adult female monarch must find a milkweed plant on which to lay eggs, the eggs must survive long enough to hatch, the tiny caterpillar (a true eating machine) must then pass through four growing stages (instars) before it crawls to a suitable location and “hardens” into a chrysalis, and then the chrysalis must survive several more days before an adult butterfly emerges. All the while, each stage – adult, egg, caterpillar, chrysalis, emerging adult - is subject to cold, heat, aridity, and numerous predators and parasites.
Monarchs, an insect that appears extremely fragile with delicate wings, each fall guides itself thousands of miles over terrain it has never seen before to an isolated site in the high mountains of central Mexico. And in a very few weeks it will head back north. Look twice at these marvelous creatures as they pass through South Texas.