Every year North America is home to an incredible wildlife migration taking place on a very small scale; that is, butterflies migrate hundreds, and sometimes thousands, of miles from areas of colder climates to warmer areas in pursuit of food and breeding habitats. Butterfly migrations are certainly quiet compared to bird migrations and whale migrations. However, there is nothing quiet about these migrations being quite as impressive.
One of the most well recognized migrators is the monarch butterfly. Millions of monarchs will migrate each fall from the northern U.S. and Canada into southern states in the U.S. and into mountainous regions of Central Mexico. In Central Mexico, many of the migrating monarchs cluster on trees during the winter months. While many of the migrating monarchs that originate in Western U.S. states will migrate to coastal areas of California.
What is unique about this migration pattern is that no single monarch butterfly will complete its entire life cycle (i.e., hibernate, emerge in spring, lay eggs along the route and repeat) every year. Summer generations of monarch butterflies do not survive through the winter, while older generations that migrated south in the fall of the previous year will survive through the winter and then start migrating north in early spring. During this migration northward, they will lay eggs in various locations along their migration route. Offspring generated from these eggs will complete the migration back to their original area(s).
While the monarch butterfly is not the only butterfly species involved in migratory patterns, painted lady butterflies are also known for significant migrations. Large numbers of painted lady butterflies will migrate across parts of the Western United States at times. This migration has been observed as large groups of orange and black butterflies flying over populated areas and has surprised many observers. Like the monarch butterfly's migration, the timing and extent of painted lady butterfly migrations can be influenced by such factors as rainfall and availability of nectar sources (e.g., desert wildflowers).
In addition to these larger-scale migrations involving larger numbers of butterflies, several other butterfly species make smaller-scale migrations based upon changes in temperature and daylight hours. Examples include red admiral, cloudless sulphur and question mark butterflies which tend to migrate south as temperatures decrease and return north when temperatures increase again. These migrations may vary from year-to-year depending upon environmental conditions, however, they demonstrate the ability of butterflies to adjust their behavior in response to seasonal changes.
Scientists continue to investigate how butterflies accomplish accurate migrations. It appears that monarch butterflies utilize visual cues (such as sunlight), internal biological clocks and possibly even Earth's magnetic fields to guide their migrations. Although butterflies are relatively small animals, they are capable of traveling to destinations that they have never previously visited.
In addition to demonstrating remarkable abilities for navigation, these migrations highlight potential environmental threats facing butterfly populations. For example, habitat destruction, pesticide use, drought and climate change may all contribute to reduced availability of nectar-producing flowers and/or host plants required by certain butterfly species. Specifically, monarch butterfly larvae rely on milkweed for food sources. Therefore, declines in milkweed availability may directly impact monarch butterfly populations.
Individuals can assist butterfly conservation efforts by creating habitat (for example, by planting native flowers) within their own neighborhoods. Individuals can also grow milkweed in suitable locations where possible, and attempt to minimize their use of chemicals within garden settings. Even a small area of habitat can serve as both a source of food and shelter for butterflies during their migrations.
North American butterfly migrations demonstrate that strength does not always require large size. At times, strength may manifest itself on bright wings and occur seasonally and quietly.