The Fantastic Journey of the Monarch Butterfly

The Monarch or Milkweed butterfly is perhaps the best known example of Butterfly migration.

Every autumn huge numbers of Monarchs fly south from their northernmost breeding grounds in Canada, an amazing feat considering none of them have made this journey before – they all hatched from this year’s eggs! Some travel over 3,000 km (1,800 miles), at an average speed of up to 50 kph (30 miles per hour).

The western population winter in California where they hibernate in many different places, mainly by the sea.

The eastern population is separated from the western one by the Rocky Mountain range, and these fly to Mexico. No one knew where they went until 1975 when they were discovered in gigantic numbers in two small areas of forest.

Here is a wonderful piece written by an American visitor, Bob Pyle, quoted in 'Butterflies of Great Britain and Northern Ireland' by Professor Jeremy Thomas(National Trust/DK publication).

‘Imagine yourself basking on a Mexican mountainside…it is snowing, snowing butterflies. Monarch butterflies fill the sky and eclipse the sun; Monarchs falling, drifting, sailing and gliding; Monarchs every shade of orange as the sun backlights or falls full upon them; pumpkin, salmon or flame. They alight on every surface, and every purple Senecio supports a dozen drinkers, every bough a hundred baskers. Monarchs alight on your boots, your belly, your face, give you a physical and mental massage of softly beating wings. So many butterflies flutter that a soft rushing whir fills the mountain air – yes, you can actually hear the Monarchs.’

‘The rustle continues, unabated for a second, until the sun begins to fall below the firs. Only then do the millions of migrants start to settle back onto the Oyamels for the night, clinging to every needle so thickly that they form a layer like the reddest fox fur. The it becomes a still world of orange butterflies – walls of Monarchs, curtains, solid tree trunks, boughs, and the whole forest groves of Monarchs, with scarcely a green needle showing through. The sun goes down and a chill rises. Having caught the last beams… the masses close their wings and become ashen scales against the dark foliage of Firs.’

Small numbers of Monarchs reach the southwest counties of the UK in most autumns – probably as a result of being blown off course by hurricane winds and hitching rides on transatlantic shipping.

There is a colony of Monarchs in the Canary Islands (established as a breakaway from the US population)  and another recently established one on mainland Spain, but it is generally thought that our autumn Monarchs come mainly from America.