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Pest Control in the Pacific Northwest

Extreme topographical and weather variations make pest control in the Pacific Northwest all that more interesting.


Greetings from the Pacific Northwest! 2016 marks PestWorld’s second visit to Seattle. PestWorld’s inaugural visit to the Northwest took place in 1989 and the pest control industry has dramatically changed since then. Seventeen years ago, fire ants and German cockroaches were the key pests of concern. Nowadays, bed bugs and mosquitoes are public enemy number one, as well as common “water cooler topics.” Similar to the pest management industry, the Northwest is constantly morphing and growing. Also, the climate and landscape are varied, changing before your eyes when traveling from the Pacific Coast further inland into the plains of Idaho.

DEFINING THE REGION. If this is your first visit to the Pacific Northwest, you’re probably asking yourself, “Which states are considered to be a part of the Pacific Northwest?” Well, the answer to that question may differ depending on who you ask, but there is one correct answer. Starting at the most western and northern point, the northwest begins in Washington state, which is bordered to the south by Oregon. East of Washington and Oregon, lays the state of Idaho, which spans the eastern borders of Washington and Oregon. There you have it…any competing definition is wrong!

The combination of rapid population growth, climate variability, and landscape diversity work in conjunction to make the Pacific Northwest a unique region for pest control. Without further ado, let’s go ahead and dive into the Pacific Northwest’s very own “PestWorld.”

Several orbweaver spiders are prevalent Pacific Northwest pests.
Photo by Rick Vetter
The Northwest is littered with mountain ranges including the Blue and Olympic Mountain ranges, with the most notable group of mountains are the Cascades, which stretch over 400 miles into Washington and Oregon from north to south. The Washington/Oregon border is also 400 miles in length and 300 of those miles are marked by the Columbia River which Lewis and Clark navigated along their travels through the Cascade Mountains. The stunning Columbia River Gorge is home to the annual Pacific Northwest Pest Management Conference, which takes place in Hood River, Ore. Portland is 60 miles west of Hood River and is growing at a rate of 40,000 new residents each year. New construction, a thriving port system, and a temperate climate transform Portland into a hot spot for a few pest species. Major pests in the city include odorous house ants, spiders and Norway rats. Rat populations in Portland aren’t as high as those observed in New York City or Seattle in part because Portland residents are required by a 19th century law to use trash cans with tight-fitting lids.

PESTWORLD HOST CITY. Seattle is three hours north of Portland and major pests in the metropolitan area include odorous house ants, Norway rats and spiders. In fact, the majority of residential pest calls in the Seattle metro area are focused on rodent and spider management. According to the Burke Museum of Natural History’s arachnid curator, Rod Crawford, one can find “100 to 300 spiders per square meter in some areas in western Washington.” Prevalent arachnids in the Seattle area are black widows, Tegeneria spp., funnel-web spiders, yellow sac spiders and a number of different orbweaver species. The most common orbweaver in Seattle is the cross orbweaver, Araneus diadematus, appearing in large numbers during late summer and fall. Cross orbweaver females are 6.5 to 20 millimeters in size and are golden-red to deep gray in color. The spider’s most conspicuous feature is the four white spots arranged in a cross like pattern on the abdomen. Recently, I visited a spider-infested 2,500-square-foot Seattle home with a technician in early August and we found more than 75 A. diadematus spiders on the exterior. Let’s just say that the homeowner was glad to see us!

BEYOND SEATTLE. Leaving Seattle and traveling towards the southeast, you’ll drive through Snoqualmie Pass to reach the Columbia River Basin. The Cascades cast a rain shadow over eastern Idaho, Oregon and Washington. Seattle receives approximately 40 inches of rain per year while cities and towns in the Columbia Basin receive 6 to 15 inches per year. Due to the lack of rain, the Columbia Basin is classified as a semi-arid shrub-steppe desert environment. One of the largest mid-metropolitan areas in the Columbia Basin is collectively known as the Tri-cities, consisting of three cities: Richland, Kennewick, and Pasco. The Tri-cities are located at the confluence of the Columbia, Snake, and Yakima rivers with the Columbia being the largest. Jeff Records, pest supervisor with Senske Services, stated that house mice, odorous house ants, pavement ants, harvester ants, yellow jackets and orbweaver spiders are routine residential pests. Records also said that he trains his technicians to inform customers living on or near one of the three rivers that effective spider management may take multiple visits because mayflies and caddisflies commonly emerge from the river providing the spiders with a consistent food source.

Although not a common pest, the Tri-cities lack of rain and shrub steppe environment provide perfect conditions for pocket gophers. According to Records, pocket gopher calls are increasing as a higher number of construction projects are underway in jurisdictions further away from city limits.

Spokane, Wash., is the second largest municipality in Washington and lies two hours northeast of the Tri-cities. Primary pests in Spokane include moles, spiders and bed bugs. However, Spokane residents are under constant ant threat. Odorous house ants, pavement ants, and two carpenter ant species are consistently found in and around homes. The Western carpenter ant, Camponotus modoc, and C. vicinus are the most commonly encountered carpenter ants in the area. One more pest ant species common to the Spokane Valley is the velvety tree ant, Liometopum occidentale, which hasn’t been observed outside of the Western U.S. Velvety tree ants are brownish-black and red in color, polymorphic, omnivorous, and establish nests in oak, pine, alder, and elm trees. Because the ants are associated with trees and have a similar morphological profile, they are commonly mistaken for carpenter ants.

The Velvety tree ant, Liometopum occidentale, is common to the Spokane Valley.
Photo by Joe MacGown
However, L. occidentale is not associated with structural damage. The ants also produce an odor similar to odorous house ants when crushed. Management efforts for L. occidentale include the use of liquid baits and perimeter sprays to discourage foraging. In addition to housing multiple pest ant species, Spokane is home to the Pacific Northwest’s leading ant expert, Dr. Laurel Hansen of Spokane Falls Community College. Hansen has served the area for over 30 years and continues to transfer her general ant and carpenter ant knowledge industry-wide.

The final city in our journey through the Pacific Northwest is Boise, located in southwestern Idaho. Boise and the surrounding towns comprise the third largest metropolitan area in the Pacific Northwest. Boise has an elevation of 2,700 feet and receives nearly 20 inches of snow during the winter months. The area is defined as having a semi arid climate and supports many of the same pests observed in the Tri-cities and Spokane. Odorous house ants, spiders, house mice, deer mice and earwigs are the targets of many pest control companies in the area. Box-elder bugs emerge in large numbers during the cooler months and the brown maromated stink bug has found its way to the area as well but is not established yet.

MORE THAN PESTS. The Pacific Northwest is full of beauty, rich history, great food, wonderful people and pests as you can see. Pest management in the region is heavily influenced by the geography and climate, making pest control difficult at times. But, the challenges we face each day provide pest professionals with an opportunity to do something different day-in and day-out. Also, if you have a conversation with a technician from Idaho, Oregon or Washington I can guarantee that the individual will possess pest knowledge and an understanding of the landscape. As a newer transplant to the Pacific Northwest, I welcome you! Enjoy PestWorld but also take some time to visit the Chihuly Glass Gardens, Pike Place Market or the Hammering Man (aka the “Hardest Working Man in Seattle”). Here’s to a great time!

by Hamilton Allen