Monarch butterflies (Danaus plexippus) are remarkable insects.
After a feast of nectar, the monarchs lay their eggs on milkweed
plants. The larvae hatch and become white caterpillars with colored
stripes. They eat nothing but milkweed all summer long, growing big
and fat. Each caterpillar then attaches itself to the bottom of a
milkweed leaf and turns itself into an iridescent blue cocoon. Within
the cocoon, the caterpillar literally dissolves away and regrows as a
butterfly.
When it hatches from the cocoon, its wings are wet and crumpled up
and it's a piteous thing to behold. But in a few minutes, it manages to
inflate its wings and dry them in the warm fall sunshine and soon
it can fly away.
Many brightly colored butterflies have a taste that birds don't like. The monarch, black and orange, fits this pattern. Their bad taste comes from the milkweed plant that they consumed as caterpillars. The colors are a warning to birds - ``You won't like me.'' But there are other species of butterfly, quite unrelated to the monarch, that turn this to their advantage by imitating the color and pattern of the monarchs. Birds usually avoid these species as well, although they would taste just fine (to a bird).
The monarch may be the only insect that makes a seasonal migration. Each fall, monarch butterflies living east of the Rocky Mountains fly by the millions to a winter habitat in the Mexican state of Michoacan. The delicate and seemingly fragile insect flies up to two thousand miles to reach Michoacan and reverses the journey in the spring.
All these millions of butterflies congregate at only a few tiny sites in Michoacan. Trees there are covered with tens of thousands of butterflies, a sight that attracts tourists to these remote destinations.
Although monarch butterflies are not an endangered species, they are vulnerable to a possible loss of this restricted winter habitat. Until recently Mexican loggers had been cutting trees from on the butterfly refuges, but the Mexican government has now designated most of these refuges as protected sites. In January of 2001, a snap of cold weather in Michoacan killed millions of monarchs at one site.
As befits such a beloved insect, there are monarch ``fan clubs''. One, called the monarch project, has been collecting and tagging monarchs for years. Beginning in 1966, the number they have been able to collect has increased each year, approximately tripling by 2000. This roughly corresponds to the adoption of Bt corn in the midwest, although it might also be due to weather or other factors.