Whidbey provides rare habitat for vulnerable moth

On the windy, glacial, ever-changing beaches of Whidbey Island grows a perennial flower, the yellow sand verbena, which is the sole home of a rare moth. Without the flower, there is no moth. The sand verbena moth has been recorded in only a few beaches in British Columbia and Washington, and two of them are on Whidbey.

While they will soon disappear to the shadows, now is one of the last chances to see sand verbena moths this season. Adults appear toward the end of May, grow to their biggest numbers in June and persist through the beginning of July. As they tuck away during the day, following the perimeter of sand verbena blossoms with a headlamp at twilight will reveal the rare moths collecting nectar.

Sand verbena moths begin as green caterpillars with light stripes, turning brown as they age. After metamorphosis, adults grow three-quarter-inch brown wings with bright yellow and black lines.

The species was described as new in 1995 via specimens pulled from Deception Pass. British Columbia listed the moths as endangered under its Species At Risk Act in 2005, but it received no such recognition in Washington and is currently a candidate to be considered endangered, threatened or sensitive. NatureServe, a non-profit organization providing national conservation data, lists the moth as critically imperiled.

While there hasn’t been a documented decline, any change to these few, narrow strips of land the moths call home could mean extinction.

Deception Pass and Rocky Point have some of the smallest populations of moths compared to elsewhere, because fewer sand verbenas can grow there.

“Unfortunately (Deception Pass is) such a high recreational use area, and the dune habitat is limited already,” said Julie Combs, sand verbena moth lead with the fish and wildlife department. “They are in very low abundance compared to the two larger sites in America.”

While sand verbenas would survive without their counterpart moths — bumblebees and other native bees pollinate during the day — they would notice a departure, and it may cause some stress.

Since sand verbena moths specialize to the sand verbena, they have adapted to become perfect pollinators of the flower. They have long proboscises, tongues, that allow easier access in the long flower tubes. Their large bodies and hair allow easier pollen pick-up and transfer. There are many pollinators, but none are quite as proficient or efficient for sand verbenas as their namesake moth.

The two species have evolved together through many millennia, Combs said, shaping each other over time. The absence of the moth may not outright destroy the flower, but it could lower its reproductive success.

Sand verbena moths are so tied to sand verbenas that the plant hosts the moth in every single life stage, Combs said. As a larva, the moth is feeding on the leaves; as an adult, the plant serves as the moth’s primary home. Adult female moths lay eggs in the buds of the flower.

“It has this really interesting relationship where it’s both a pollinator in the adult stage and an herbivore in the larval stage,” Combs said.

The hyper-dependence between the plant and the moth species is somewhat rare among moths, Combs said. Moths are usually generalists, finding nectar in any number of plants. Sand verbena are one of a few unique specialists.

But they aren’t the only ones. Eastern Washington hosts three moth species which share a genus with the sand verbena moth which have similar needs. Washington lists these species as the greatest conservation need—like the sand verbena moth, they are limited to dunes. Unlike the sand verbena moth, they appear to have a bit more complicated plant host needs that researchers have yet to pin down.

The fish and wildlife department recommends using herbicide and machines to open sand dunes and expand moth habitat. Currently, state parks employees at Deception Pass are making efforts to restore sand verbena moth habitat.

Their summer visibility is special, Combs said, because when surveyors run detection surveys to see population strength, they hardly see the moths then. Researchers use traps and check them at midnight with blacklights.

For those witnessing the moths, be conscious of the environment to not trample any vital sand verbenas and generally follow park rules and signage.

Inside the trap, researchers can see the sand verbena moth at Deception Pass. Note from sand verbena moth lead Julie Combs: “This sampling scheme is not destructive. We catch them, count them and then release them. Six moths were found at this trap.” (Photo courtesy of Jenny Shrum)

WDFW surveyors set up a moth blacklight trap at Joseph Whidbey State Park. Note from sand verbena moth lead Julie Combs: “We didn’t find the moth here, not enough host plants.” (Photo courtesy of Jenny Shrum)