A Washington agriculture department entomologist said Tuesday he was hopeful that Asian giants hornets have been contained in Whatcom County and will be eradicated.

Sven Spichiger told the Senate agriculture committee that all four nests found in the past two years were grouped near the U.S.-Canada border, about 110 miles north of Seattle.

One hornet was trapped less than a mile away in British Columbia in October, but was probably a straggler from one of the nests eradicated earlier in the U.S., Spichiger said.

No other hornet was confirmed on either side of the border this summer or fall, though the department, other agencies and volunteers put up more than 1,600 traps.

“We are very cautiously optimistic that we still have a very contained event,” Spichiger told senators at a pre-legislative session workshop.

“As long as we keeping working on it and get the awesome support we’ve gotten from everybody, we can hopefully wrap this one up,” he said. “We don’t often get to say that with invasive insects.”

Asian giant hornets are the world’s largest hornets and have a painful and occasionally fatal sting to humans. They prey on other insects, including pollinators such as honey bees.

The hornets were unknown in North America until appearing in British Columbia and Whatcom County in 2019. No nest has been found in B.C., and sightings have been rarer.

The Washington agriculture department destroyed one nest in October 2020 and three more this year. The nests were all within an area about 3 miles long.

The department suspects that unmated queens had left the nest last year by the time it was destroyed and survived to form the three nests eradicated this August and September.

Nests this year were found early enough to prevent them from being the source of more unmated queens, department spokeswoman Karla Salp said.

The department can’t rule out that Asian giant hornets have spread beyond the immediate area of the destroyed nests.

The department received a photo Sept. 6 of a flying insect near Mount Sumas, farther east in Whatcom County.

The insect resembled an Asian giant hornet. The department said the report was concerning, but it could not positively identify the species.

Some Asian giant hornets were trapped last year in Whatcom County and British Columbia outside the area where the nests were found.

One dead specimen was found in June near Marysville, about 80 miles south of the eradicated nests. Entomologists don’t know how the hornet get there, but believe it was from the previous year.

Salp said the department probably will conduct a trapping campaign in 2022 similar to the one this year.

Asian giant hornets have shown they can survive Northwest winters, she said. Specimens put on ice in coolers and even stored in freezers have revived.

Although the hornets are ground nesters in their native habitats, all four nests found in Washington have been in dead alder trees.

“Western Washington is essentially ideal habitat for them,” Salp said.