Meet the Monarch
California is home to a wide variety of pollinators including western monarchs and other butterflies as well as bees, flies, moths, and other insects. Fully 87% of all plant species require animal pollination. Without pollinators there would be no cornflowers, poppies, foxgloves, or forget-me-nots. And 75% of our crops require pollination by insects.
Monarch butterflies (Danaus plexippus) are found across North America. The western monarch ranges throughout California and most other Western states.
Monarch Life Cycle
Monarchs undergo a complete metamorphosis from an egg to a larva (AKA caterpillar), then to a pupa (chrysalis) and finally to a butterfly. While these stages look very different, the physical changes occur continuously throughout the metamorphosis. For example, the wings and other adult organs of the butterfly develop from clusters of cells already present in the caterpillar.
The life of a monarch begins when the female butterfly lays a tiny egg on a milkweed leaf. She secretes a special kind of glue to attach the egg firmly to the leaf. Then she flies from one plant to another, laying hundreds of eggs over the next two to five weeks.
After about four days, the caterpillar emerges from the shell, and begins nibbling on milkweed leaves. The milkweed is the only plant that monarch caterpillars will eat, making this unassuming plant essential to the survival of the entire species.
The caterpillar consumes a lot of milkweed over the next two weeks, growing to almost 2,000 times its original mass. Home gardeners should not be surprised to see a single caterpillar strip a two-foot tall milkweed plant of all its leaves. During this period, the caterpillar also molts five times, each time emerging in a new skin. These five stages are referred to as “instars.”
After two weeks, the caterpillar is ready to pupate. It spins a silk mat from which it hangs upside down, shedding its familiar yellow, white, and black striped skin for the last time. Its new layer of skin hardens into a pupa, or chrysalis.
After 8-15 days, the black, orange, and white wing patterns of the butterfly are visible through the pupa covering. This is not because the pupa becomes transparent; it is because the pigmentation on the wings develops at the very end of the pupa stage.
When the butterfly emerges from the pupa, its abdomen contains mostly body fluids. Its wings are shrunken and crumpled looking. The adult hangs upside down and pumps fluids into its wings until they expand and stiffen. Then it flies off to feed on nectar plants. In 3-8 days, the butterfly reaches sexual maturity and is ready to mate.
The newly emerged butterfly is ready to begin life as a pollinator. When it visits a flower in search of nectar, pollen from the stamen of the flower may accidentally attach to its legs. When it moves to the next flower, that pollen may brush on to the plant’s stigma, fertilizing it and thereby allowing it to produce fruits and seeds.
Monarch Migration
Western monarchs are well known for their epic migratory voyage when they leave their overwintering sites along the California coast and head east for the spring, summer, and fall. Successive generations during this migration period spread throughout the Western states, feeding on nectar, mating, and laying eggs.
The fourth generation heads back to the coast, where it spends the winter roosting with other monarchs, leaving the cluster only to find nectar. Not until February or March do members of this generation head out, searching for milkweed and starting the cycle over again.
The Western monarch overwintering sites are mostly located along the coast between Mendocino and San Diego County within five miles of the ocean. They look for large trees where they can shelter from wind, rain, and predators. They often select eucalyptus trees, Monterey pines, and Monterey cypresses as roost sites, as well as oak, sycamore, and redwoods.
Overwintering monarchs
