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Hornets, crabs and rodents: setting traps to locate and contain invasive species

While media reports were raising alarms about an invasion of dangerous “murder hornets,” Washington state entomologists were quietly planning a trapping program, which will mark the beginning of a search-and-destroy mission against the Asian giant hornets.

Trapping has become a primary tool in the early detection of invasive species. Traps are often used to control or reduce breeding populations of destructive pests — from insects such as the gypsy moth to rodents such as nutria to aquatic organisms such as the European green crab.

Officials with the Washington Department of Agriculture say they are hoping the Asian giant hornets can be eradicated from Washington state or at least kept under control, as we’ve seen for gypsy moths and green crabs.

Asian giant hornet // Photo: Washington State Department of Agriculture

Sven Spichiger, managing entomologist for WSDA’s Pest Program, said it was disappointing to learn that this new species of hornet was able to survive the winter in Western Washington. But that doesn’t mean that we must tolerate this dangerous insect, which can literally kill every honey bee in a hive.

“It is my belief that it is still very early on for any sort of infestation, which gives us an excellent opportunity to use everybody’s eyes and ears, find out where it is and wipe it out where we find it,” Sven during a press briefing recorded on YouTube.

In the first trapping program for Asian giant hornets, WSDA trappers will install about 300 traps in Whatcom County near the Canadian border. It’s where the first-ever queen was found in Washington state on May 27, not far from where a worker hornet was found in December.

Where Asian giant hornets are picked up in traps, experts will search for active underground nests and carefully destroy them. If they can catch hornets alive, they could try out a miniature tracking device to see if the hornets can lead them to a nest, Sven said. The trapping effort will begin in July before the worker hornets are expected to emerge from the nests.

Although these hornets really are quite large and bear over-sized stingers, officials stress that they do not normally attack humans or pets unless they are threatened. Information about Asian giant hornets, including how to identify and report them, can be found on the WSDA hornet page.

Meanwhile, trappers will continue to put out gypsy moth traps — some 20,000 this year — throughout Washington state. Some will be placed at high density to reduce the number of moths in some areas, while others will be placed at low density to locate new infestations. Two areas of Snohomish County are designated for eradication by using aerial spray. See “2020 eradication information.”

European gypsy moth // Photo: John H. Ghent, USDA Forest Service

The effort this year involves both types of invasive gypsy moths: 1) the European gypsy moth, which often comes to the Puget Sound region from established areas in the Eastern United States, and 2) the Asian gypsy moth, which can devour our Northwest evergreen trees.

Infestations of Asian moths are more worrisome, because both males and females can fly, making their spread faster and less predictable. Females of the European variety generally don’t move very far. See “Gypsy moth in Washington” (PDF 2 mb).

Trapping for other invasive insects varies by year. They can include other tree pests, such as emerald ash borer and sirex woodwasp; fruit pests, such as apple maggot and European grapevine moth; and wide-ranging destroyers of a variety of plants, such as Japanese beetle and light brown apple moth. See “Invasive Insect Detection” (PDF 1.2 mb).

The COVID-19 pandemic has caused some changes in the trapping protocols this year. Before placing a trap, officials with the WSDA typically check with the land owner, even though state law gives them authority to place a trap on private property. This year, due to concerns about spreading the coronavirus, trappers — who will wear a safety vests with “WSDA” on the back — will follow a “no knock” policy. Property owners who have questions or object to the traps may call (800) 443-6684.

Among the aquatic invaders in the Puget Sound region is the European green crab, which showed up in Puget Sound in 2016. The trapping program, which started before the first invasive crab arrived, has been credited with locating small populations of the destructive crabs before they could gain a permanent foothold. Where green crabs are found, trappers put out many more traps to curb the population.

A small male European green crab found at Dungeness Spit.
Photo: Allen Pleus, WDFW

Washington Sea Grant’s Crab Team, a major volunteer effort that conducts trapping and identification, was recently honored with the SeaDoc Society’s 2020 Salish Sea Science Prize, as shown in a video on YouTube.

Eric Wagner recently wrote an article for the Encyclopedia of Puget Sound explaining how the green crab trapping program has continued despite COVID-19. See “Search for invasive green crab continues during pandemic.” My coverage of green crabs goes back to just before the first invader was found in 2016, when I examined a variety of invasive species threats. See “Invasive stowaways threaten Puget Sound ecosystem.”

A lesser-known aquatic invasive species that has placed officials on high alert is the African clawed frog, a species found in two groups of stormwater ponds, one near Lacey and the other near Bothell. The ponds discharge to natural water bodies, and both areas have been actively trapped to control the frog populations.

Native to sub-Saharan Africa, African clawed frogs are considered a severe threat for their ability to out-compete and even consume native frogs. Similar to bullfrogs, these clawed frogs can eat just about anything that fits into their mouths, including small fish and birds. They also are known to carry diseases that can kill other amphibians as well as fish. These imported frogs were commonly used in laboratories and classrooms.

Also found in ponds and wetlands, beavers historically were trapped for their fur, but today there is a growing recognition that they provide important aquatic habitat to help certain species of salmon. Such cannot be said for the distant relative of the beaver: an invader called nutria, a semi-aquatic rodent that burrows into embankments, destroys wetland vegetation and displaces established beaver populations.

Nutria // Photo: Washington Invasive Species Council

Nutria were first brought to the Northwest from South America to be raised for their fur on local farms. In the 1940s, the demand for fur declined and most farms went out of business. Some of these animals have survived in the wild, with large numbers reported in some areas, including Lake Washington. Organized trapping efforts have been attempted but never sustained.

Washington residents can get a better understanding of invasive plants and animals with with a smart phone app called “WA Invasives,” available from the Apple App Store or Google Play. The app includes pictures of the dozens of invasive species with a process to report the location of sightings. See also “Report a Sighting” on the website of the Washington Invasive Species Council.

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