Nebraskaland

30 NEBRASKAland • APRIL 2015 T he migration of the monarch butterfly, an icon of the insect world if there is one, is one of the great mysteries of the world. The drastic decline – 90 percent in 20 years – in the number of monarchs making that annual fall flight to central Mexico is no mystery. Habitat loss, especially in the upper Midwest, is the primary cause of the species' decline. Whether the decline can be reversed, or even stopped, so that migration can continue is yet to be seen. But work is underway on many fronts. On one, environmental groups have proposed giving monarchs protection from the Endangered Species Act. On another, many groups are working to plant more milkweed, with some monarch lovers even tossing seed bombs out their car windows to propagate the species on roadside ditches. The decline in this colorful native plant is believed by many to be the root cause of the monarch's decline. The species only lays its eggs on milkweed, which serves as the food source for its larvae. And with fewer plants on which to lay eggs, there have been fewer adults to complete the migration. The Monarch's Year The life of each monarch we see in Nebraska, and every one east of the Rocky Mountains for that matter, can be traced to a volcanic mountain range in central Mexico. There, a super generation of monarchs that lives longer than any other spends the winter. Tens of millions of the butterflies arrive in November and cluster on oyamel fir trees in south facing slopes at elevations of 10,000 feet. There, it is cold enough to slow the insects' metabolism, but not cold enough to freeze them to death. Monarchs can't handle cold like some insects, a fact that drives their migration. These overwintering sites were only discovered in 1975. To that point, they were known only to local villagers, who have since become guides for tourists who come to witness the spectacle, and caretakers of the land, much of which has been protected by the Mexican government. Monarchs begin flying north in March, following the emergence of milkweed. When they leave Mexico, they push the play button on sexual development that had been in suspension since they began their southward migration months earlier. This super generation, with its wings weathered and less colorful that monarchs we see, lays eggs from northern Mexico and Texas to as far north as Kansas, Missouri and Virginia, and then dies. The generation it produces continues the northward movement, fanning out across the United States and into southern Canada, where it also reproduces and dies. The offspring of this second generation are the monarchs we see throughout the summer. They begin as eggs laid from late-May through July. Some emerge early enough to produce a fourth generation from eggs laid from late June through August. Unlike earlier generations, which are able to reproduce within days of emerging, these third and fourth generation adults emerge in reproductive diapause, with their reproductive organs stalled in state of suspended development. These changes, and the start of the migration, are triggered by shorter days, cooler temperatures and changes to the milkweed plants. In the northern monarch range, migration begins in late August. Migrating monarchs typically begin to arrive in northern Nebraska in early- September. By the end of the month, most monarchs have left the state. Native to North and South America, monarchs spread to Hawaii, Spain, Portugal, Australia and New Zealand and other parts of the world in the 1800s, most likely with help Story and photos by Eric Fowler Monarchs Habitat loss threatens colorful insect's future

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