Photos and story by Stephanie Hazen
During the second week of June, the first monarch butterflies, Danaus plexippus arrived in the Willamette Valley from their wintering grounds along the Southern California Coast. Several dozen monarchs of these northward bound migrants found the Showy Milkweed, Asclepias speciosa, and Narrow-leafed Milkweed, Asclepias fascicularis, growing at a heritage seedling nursery.
These two species of Asclepias are the only two milkweeds native to the Willamette Valley. Milkweed is the only plant on which monarch eggs will complete their life cycle from larva to caterpillar to chrysalis to adult butterfly.
According to a 2015 report published by Xerces Society, the overwintering population of monarchs in Mexico that migrate to the eastern and Midwestern US has dropped 90% from the 20-year average. As of 2014, the western monarch population had declined by an estimated 50% from the long term average. These declines are so severe that a group of biologists has petitioned the U.S. Fish and Wildlife Service to list the North American Monarch as a threatened species under the U.S. Endangered species Act (Center for Biological Diversity et al. 2014).
In 2006 under permit from ODOT, Lynda Boyer, Native Plant Manager for the heritage nursery collected seeds from a showy milkweed population growing in the right to way that would have been lost during construction of a new interchange west of Salem. Through trial and error, Lynda turned a handful of seeds into one-third acre of these Willamette Valley native milkweed plants.
Harvested by hand from the production fields, these labor-intensive milkweed seeds find themselves sown in large-scale native prairie restoration projects. 2015 is the first year that monarchs have come to Linda’s plantings in such large numbers.
The United States is host to two distinct populations of monarch butterflies: one east of the Rocky Mountains that overwinters in Mexico and the population west of the Rockies that overwinters along the coast of Southern California and Baja Mexico.
Every spring the butterflies migrate north in search of milkweed plants on which to lay their eggs. Equally important, they are looking for native flowering plants on which to obtain nectar to maintain their nutritional needs. They need flowers that bloom spring, summer, and very importantly in the fall when they migrate back to California. Spraying herbicides, as well as mowing fields and roadsides, can greatly reduce the flowers they need for return to their wintering grounds.
It takes 30 days and five stages for the monarch to metamorphose from egg to larva to caterpillar to chrysalis to adult butterfly. If the weather holds up, and the food sources last, the monarchs at the seedling nursery may create 3 generations of butterflies before the last generation returns to California.
One positive development for those concerned about the butterflies’ survival is legislation mandating that all plantings along the length of US Highway 35, the major north-south interstate in the central United States that runs between Laredo Texas to St. Paul, Minnesota – must now be native plants.
Salem Weekly readers who want to learn how to participate in “citizen science” and report the monarch butterflies that you find, visit, https://www.learner.org/jnorth/. Those who want to learn about monarch butterflies or learn how to grow milkweed, visit : http://www.xerces.org
Stephanie Hazen is a Salem area retired small animal veterinarian, amateur photographer, and avid amateur naturalist.