In March, monarch butterfly watchers around North America were gratified to see the air fill with millions of the fluttering orange and black wings as a new population left the safety of the fir forests of Oyamel, Mexico and headed North on a journey that could be as much as 3,000 miles.
After a decade of decline, the monarchs seem to be making a comeback, thanks to changes in the weather and some new agricultural practices that include a concerted effort to preserve milkweed along the route of their northward trek.
Milkweed, (Asclepias) is the only plant upon which the butterfly will lay its eggs and the only plant upon which the larvae will feed. Laying her eggs on milkweed gives the young protection from predators because the milkweed makes the larvae toxic.
Monarchs overwinter in Mexico, roosting on the fir trees in Oyamel forest where they cluster by the millions, clinging to the trees and each other for warmth and protection against rain. Monarchs cannot withstand temperatures much below 13 C. Their flight muscles stop working if it’s too cold.
In fall, the last generation of monarchs for the season do not develop sexual equipment (a feat known as diapause) to preserve the energy needed to make a trip that can cover 2,000 to 4,500 km. This is the methuselah generation, so called because, while most monarch have a lifespan of two to six weeks, this last hatch lives eight months. It must survive the long flight back to Mexico, overwinter and have enough strength to fly the first leg back north where it can mate and lay its eggs on the milkweed.
In fall, if you look way up you will see them roosting in the trees along the route. They may visit for two or three days if there is a hearty meal of nectar nearby. The heavy nectar producers include Joe Pye weed, New England aster, turtlehead, meadow blazing star, bergamot and goldenrod.
The monarch is an amazing flyer. It can put 75 kilometres a day behind it, flying at speeds of 19 km per hour. Some tagged butterflies have been known to fly 250 miles over water without stopping. They have been seen flying as high as 11,000 feet.
Monarchs navigate using the magnetite in their antennae, but it is still a mystery how they know where home is when there are many possibilities.
Monarchs have a particularly lovely way of mating. The resting female is pounced upon by an eager male, which attaches himself to her posteriorly, then lifts her gently into the air to the branches of a tall tree to be safe from danger. The coital act takes one-and-a-half to two hours and, when the sperm injection is complete, she flies off to the nearest milkweed to lay her eggs.
Monarchs have been accused of being insect imposters with only four legs, but in fact, they have six. The forelegs are tiny and folded up so you can’t see them. A look-alike butterfly, the viceroy, is the real imposter. It has very similar markings and colouring. But look closely – the imposter has a secondary black ring on the centre of its wings. In spring, you will find the larvae of these cheats rolled up in a willow or poplar leaf. They emerge about 15 days after their host trees have leafed out.
Monarchs, on the other hand, arrive much later, in full beautiful flight bringing delight to our gardens and to thousands of children who have had the experience of observing their miraculous metamorphosis.
Abiove, a monarch rests on swamp milkweed, Asclepias incarnata ‘Ice Ballet’.
Milkweed varieties
Milkweed has the most beautiful and varied flowers.
Then construction of the flower is fascinating, with a centre part that includes a “horn” and a “hood” that surround the stigma and anther and are upright tin the centre of the flower. These are surrounded by a set of reflexed petals called corolla, often in a contrasting colour. The flowers grow in umbel shaped clusters.
People with a farming background might hear the word “milkweed” and be horrified as the wild plant, Asclepias syrica, spreads alson rhizatous roots and is not fussy about its terrain, doing well in dry to medium soil and full sun. Best choose a tamer variety.
There are actually 13 varieties native to Canada. The following examples all have tap roots and stay put.
Butterfly milkweed, Asclepias tuberosa is an excellent choice. It grows 1 to 1.5 feet tall. It blooms June to August with a pretty yellow and orange flower and likes full sun and dryer conditions. Unlike the other milkweed, it does not have a sticky sap.
Swamp milkweed, Asclepias incarnata, is perfect for that wet corner of the yard, but it will survive in medium soils and full sun. It gets a lovely while or pale pink flowers surrounded by a darker pink corolla and sepals. “Cinderella’ is pink. ‘Ballerina’ is creamy white.
Green milkweed, Asclepias viridis, has baseball-sized pale green flowers. Height is 18 to 30 inches. Again, this is a full sun plant that thrives in dry to medium soil. Zone 4.
Showy milkweed, Asclepias speciosa, also called silkweed and white Indian hemp, has clusters of pinky-white, starry flowers. This plant boasts large, oval, velvety, blue-green leaves. The seed pods are also showy with ling, silvery-white, silky hairs. This one is native to the western part of the country.
What to plant
If you want to have monarchs in your garden, plant nectar-rich flowers. Make sure your choices bloom in fall to give the monarchs the energy they need to make the long journey south
Perennials
Milkweed (Asceplias) all kinds.
Common yarrow (Achillea)
New England aster (Symphyotrichum novaeMilk-angliae)