The winged beauty’s annual voyage is one of the most extraordinary in the natural world
Mike Dilger’s WILDLIFE SPECTACLES The broadcaster, naturalist and tour guide shares the most breathtaking seasonal events in the world
MIGRATING MONARCH BUTTERFLIES
When contemplating epic animal migrations, the first journeys that spring to mind will invariably be the massed movement of wildebeest across the African plains, the globetrotting adventures of Arctic terns, or the oceanic odysseys of gray whales. But let’s not forget the annual cycle of the monarch butterfly, which is surely as impressive as anything an antelope, bird or whale can muster.
In possession of two pairs of brilliant,
large orange-red wings, etched with black veins and decorated with white spots along dark margins, the monarch must surely be the most easily recognised and best-loved of all North American butterflies. Rarely lasting for longer than a month on the wing, the monarchs nonetheless provide an important service pollinating countless wildflowers over the summer.
However, with the arrival of autumn, a special ‘Methuselah generation’ of monarch butterflies, which can live eight times longer than their predecessors, emerges from summer breeding grounds across Canada and northeastern USA. Forced
south by decreasing day length, lower temperatures and fewer nectar sources, the final winter destination for these butterflies consists of just a few hectares of high-altitude forest in south-west Mexico, up to 4,800km away from where they started life
as an egg.
Migrating only during daylight hours, the butterflies will travel anywhere between 148km and 185km per day, with their speed dependant on wind direction and uplifting thermals. Gliding and flapping their way steadily south, coalescing into super-flocks en route, they’ll pour across the USA-Mexico border before making a ‘butterfly-line’ for the forests of oyamel fir trees situated west of Mexico City.
How these butterflies know where to go is the source of considerable debate. Each migration is undertaken by a new generation, meaning they’re unable to learn the route from others, so it must be genetically hardwired. It’s also believed their antennae have circadian ‘clocks’ that tell them when to migrate, while navigation may well be accomplished by using their compound eyes to calculate the sun’s pos
