Giant hornet effort approaches milestone as another pest shows up  - Salish Current
February 26, 2024
Giant hornet effort approaches milestone as another pest shows up 
Lane Morgan

They’re coming for you … if you’re a northern giant hornet or perhaps a spongy moth … although they may not be wearing these over-the-top suits. Washington State Department of Agriculture workers did don the suits in removing a hornet’s nest in October 2020 — and they are raising an alert around the voracious, invasive spongy moths that have been seen in the Salish Sea area in increasing numbers. (WSDA)

February 26, 2024
Giant hornet effort approaches milestone as another pest shows up 
Lane Morgan


“Nest Zero” [14.40], a 2022 documentary by TVW, Washington’s public affairs network, tells how community support was a significant boost in WSDA’s eradication of northern giant hornets. (TVW)

Ed.: Updated March 2, 2024, with added images of caterpillar and adult spongy moths.

For invasive pests, whether plants, insects or viruses, an early and coordinated response is the best chance at elimination. Failing that we are likely stuck with long-term management to minimize harm. 

Northwest Washington looks to be in both of those categories with two notorious creatures.

One of them, the northern giant hornet, may be gone, at least until the next incursion. After intensive monitoring and an unprecedented effort by volunteers as well as staff, no nests or individuals have been spotted since 2021. The Washington State Department of Agriculture considers an invasive species eliminated after three years without a sighting. 

Skagit newcomer

WSDA has targeted an area north of Concrete in its efforts to eliminate invasive spongy moths. (WSDA)

Another voracious invader, the spongy moth (Lymantria dispar), is part of a 50-year high-stakes program of tracking and response by the WSDA. Last year the state’s annual survey for spongy moth found 103 moths including some nests, a big increase from 30 in 2022 and six in 2021.

The biggest concentration, 77 of them, was in the Steamboat Island Road area of Thurston County, but another trouble spot was in Skagit County, along the Baker River near Concrete. Field workers trapped 10 moths there, compared with two the year before. The numbers are small, but the creatures are prolific breeders and the risk of spread is substantial.

For Western Washingtonians, one way to think about spongy moths (known previous to their name change in 2022 as gypsy moths) is to picture a tent caterpillar infestation in a bad year and then multiply.

Spongy moth caterpillars are bigger and more destructive than our native leaf eaters and can defoliate entire forests. Their shed skins are irritating to eyes and skin and their abundant droppings can pile up to the point that sidewalks and paths turn slimy. Usually the cycle involves two or three peak years of infestation — enough to kill weakened trees and shrubs —and then a population crash. 

WSDA proposes to treat both areas in May with an aerial spray of Bacillus thuringiensis var. kurstaki, a popular biological control for pests with a caterpillar stage. BT is soil-based bacteria often used in organic agriculture for cabbage moth caterpillars and other pests. The Skagit County operation will cover about 900 acres. 

The department held a “Come and See” event on Feb. 12, in Concrete to explain the threat and their planned response. It has filed a State Environmental Policy Act (SEPA) statement and collected public comments.

Voracious, prolific, invasive spongy moths are definitely unwanted in Washington. Visual inspection for and manual destruction of egg masses is part of pest management strategy — along with reporting. (WSDA)

When the northern giant hornet tracking campaign began in 2020, WSDA entomologist Chris Looney told the New York Times, “This is our window to keep it from establishing. If we can’t do it in the next couple of years, it probably can’t be done.” 

Escape and spread

The spongy moths are an example of what can happen when that window of opportunity is missed. 

Leopold Trouvelot was a French immigrant to Massachusetts in the 1850s. Primarily an artist specializing in drawing of astronomical phenomena such as auroras, he also raised silk worms in his back yard, maintaining a collection of mulberry trees to keep them fed.

He dreamed of establishing an American silk industry, with caterpillars adapted to local food supplies. So in 1869 he brought some Lymantria dispar larvae back from a trip to Europe. His hope was to breed them with the Asian worms to create a silk-making hybrid that would eat a variety of plants instead of just mulberries and would also be less attractive to birds. 

Part of that plan worked. The newcomers adapted well and the caterpillars’ stiff bristles made them less appealing as food. Although he netted his property to keep them confined, inevitably, some escaped. Delighted with their new dietary options, the spongy moths have been spreading through towns and forests ever since, aggravating residents and causing an estimated $200 million a year in damages to woodlands. 

Washington first saw spongy moths in 1974, but has never had a full scale-infestation. WSDA has been monitoring and trapping all during that period, hoping to avoid a breakthrough population. Each year dozens of trappers set up 20,000 to 30,000 traps throughout the state to monitor for spongy moth introductions. 

“Targeted control for caterpillars with the least toxic methods effective for the site” is recommended by the state Department of Health. (WSDA)

Since 2016 it has responded to trappings by treating infested sites and their surrounding areas with BT spray, followed by three years of intensive follow-up trapping. 

Although the creatures have not been eliminated (and accidental reintroductions by travelers from other states make elimination unlikely) WSDA has set 2024 as a celebration of 50 years without a damaging outbreak. Social media posts and “Come and See” events like the one in Concrete aim to increase knowledge about spongy moths and how they can be controlled. 

Where you come in

The anniversary campaign is an example of the how the agency combines public education, specialist research and citizen science to advance its goals. Its insect-tracking campaigns make use of a combination of boots on the ground, traps in the trees, and catchy promotions on social media. 

The WSDA is a multipronged agency, tasked with regulating and supporting crop-related activities from chicken farms to cannabis. For long stretches it doesn’t get much public attention. The arrival of northern giant hornets in Whatcom County changed all that. Huge, scary bee-chomping insects spawned memes and headlines, and the moon-suited field workers who tracked them turned into media heroes. 

The hornet and moth initiatives show two sides of WSDA’s mandate and its techniques for public involvement. Karla Salp, the department’s public engagement specialist, outlined some of the considerations for citizen participation in a tracking program. It helps if the pest is easy to spot and identify without additional information such as DNA testing. Given their size and notoriety, northern giant hornets filled that bill, even though their initial numbers might be few.  

Pheromone traps capture insects and serve in monitoring populations as well. (USDA APHIS PPQ)

“I can’t think of another time where we’ve had anywhere near this level of community support,” Salp told Crosscut in 2021 about the citizen hornet trappers. She said that requests for volunteers to trap invasive insects typically garner a few dozen responses. This time was different, perhaps because of a combination of factors: The hornets were a media sensation; COVID shutdown restrictions meant more people were home during the day and eager for diversion; their threat to honeybees added to the feeling of urgency. 

About 900 hundred traps were set in Whatcom County in 2022, and the Washington State Hornet Watch Facebook page, administered by WSDA, now has 9,000+ members.

The project involved technologies from state of the art to spur of the moment. Volunteers followed WSDA instructions to make traps from plastic bottles baited with a mix of orange juice and rice wine from the grocery store. Later the mixture was modified to brown sugar and water — easier to find and less expensive. Then they checked their traps once a week and, during the first summer of trapping, mailed their contents to the state lab, a task with its own set of challenges. 

“Keep in mind that if you are sending it as a letter, it needs to be less than 1/4″ thick, and if you are sending it as a large envelope, aka flat, it needs to be less than 3/4″ thick and not more than 1/4″ variation in thickness” Lopez Island resident Becca Peters wrote in one post on the Hornet Watch Page. For trappers who had bumpier collections of drowned insects, she added suggestions for the cheapest way to ship a package. 

Thousands of spongy moth traps are set by community members and WSDA each year. (WSDA)

Hornets captured live by trained staff, a more daunting project, were then outfitted with a radio tracker, which also required some experimentation. The first ones were attached with glue, which turned out to make a burden too heavy for the insects to carry in flight. The solution was to tie them on with dental floss and feed a dab of jam to the hornet for extra energy as it headed home. 

In addition to training volunteer help, WSDA’s public education outreach went into high gear, much of it focused on helping nervous residents tell the difference between the new invader and other scary-looking insects that don’t pose a problem. People from all across the region reported backyard finds to the Hornet Watch website, and the agency evaluated each one.  

Hiding in plain sight

Unlike the hornets, which had one known entry point into the state, so far, spongy moths get reintroduced periodically in different areas. The moths are drab little creatures, not likely to attract attention, and Washington has never had an infestation large enough to attract attention through massive defoliation. 

Salp explained in an email that the spongy moth “is probably not one we would usually try to get the public involved with.” WSDA has developed an effective trapping system using temporary workers, and so far the moths’ “numbers are so low that the public is very unlikely to see them. However, this past fall when we caught a lot of moths (77 is a lot in the case of spongy moth) in one area, we did put out some messaging about looking for spongy moth egg masses to that very specific area.”

The current focus for newer invasive insects throughout Washington, funded by the legislature though 2025, is on northern giant hornets, spongy moths, Japanese beetles and spotted lanternflies. The lanternflies have not yet been seen in Washington. Japanese beetles are established in Yakima County, with a smaller population found in Benton County last year, but are not known to have made it west of the Cascades. An intensive eradication program is underway, and residents in infested areas have been asked to help with trapping.

— Reported by Lane Morgan


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