The information in this state update was provided by Dr. David James, firstname.lastname@example.org. Please contact him for additional information about the update.
Washington State is usually the final destination for the majority of western monarchs migrating north in spring. A few make it into British Columbia by up to 100 miles but many make Washington their summer-breeding home in most years. Most abundance occurs on the eastern side of the state although a few migrate north through western Washington and will stop and lay eggs if they encounter milkweed.
Showy milkweed is the dominant milkweed species in Washington and it is common to abundant along roadsides and in riparian areas of eastern Washington. The first monarchs are seen in early June each year in Washington and produce at least two generations. Monarchs eclosing in August may join the migrating generation and those eclosing in September certainly do.
By early October, most monarchs have left Washington State and are en route or have arrived at overwintering sites in California. A few individuals migrate in a different direction towards the south-east, through Utah and may end up overwintering in Mexico.
After two years with only a handful of monarch sightings in Washington, we will not be surprised if we do not see any monarchs in Washington State in 2021. This would be the first time in at least 20 years that no monarchs were sighted.
The reason for this pessimism is of course the extremely low overwintering numbers (less than 2000) in California this past winter. Unless the survivors from overwintering are joined by individuals from other populations in California (primarily winter breeders in the bay area) and/or progeny from migrants originating in Mexico, It is hard to see how monarchs will reach Washington this season.
However, the monarch is an adaptable and surprising creature and I do not entirely close the door on the butterfly stunning us all and finding its way to the outer reaches of the Pacific Northwest!
In a normal year, the first monarchs arrive in southern Washington during the first week of June. They did this without fail from 2004-2017. The abundant stands of Showy Milkweed in eastern Washington would then support at least two generations of caterpillars before the population migrated south during September.
All of us in Washington hope the annual visit by monarchs to our state will continue and increase in the future, but for this to happen, we need to work on the restoration of milkweed and monarchs in California, the hub of monarch ecology in the west.
Abundant Showy milkweed at a central Washington monarch breeding site that went unused in 2020.
Hands used for crime now nurturing a struggling species (KXLY News, September, 2018)
Monarch Butterflies in the Pacific Northwest Facebook page