Centipedes are common arthropods found throughout Washington State, existing both outdoors and occasionally within homes. They are often mistaken for other household pests, but they possess a distinct segmented body and numerous legs. Understanding the specific types of centipedes present in the region is key to knowing how to coexist with them safely.
Confirmation of Presence and Common Species
Centipede species are widespread across Washington, with the most frequently observed types being the House Centipede, the Bark Centipede, and various species of Stone Centipedes. The House Centipede (Scutigera coleoptrata) is the most common species encountered indoors. It is easily recognized by its long, yellowish-brown body, measuring about an inch, and 15 pairs of exceptionally long, delicate legs. These centipedes are beneficial predators within the home, actively hunting and consuming common pests like silverfish, spiders, and cockroaches.
Other centipedes found in the state include soil-dwelling species belonging to the Lithobius genus, often called Stone Centipedes. These are smaller, often reddish-brown, and have shorter legs relative to their body size compared to the House Centipede. Stone Centipedes are commonly found in gardens and forests, dwelling beneath rocks, logs, and leaf litter. The Bark Centipede, which is reddish-brown with yellow legs, is slightly larger than the House Centipede and is known to be more aggressive when threatened.
Assessing the Threat: Venom and Bite Symptoms
All centipedes possess venom, which is delivered through a pair of modified front legs called forcipules that curve around the head and function like fangs. Centipede venom is primarily used to subdue their prey, consisting of small insects and other invertebrates, and is not typically medically significant to humans. The House Centipede, despite its alarming appearance, rarely manages to penetrate human skin with its forcipules, and a bite, if it occurs, is usually comparable to a mild bee sting.
The bites from larger, native Washington species, such as the Bark or Stone Centipedes, can be more painful, as they can inject a greater volume of venom. Symptoms are generally localized to the bite site and include immediate sharp pain, redness, and mild to moderate swelling. The puncture marks from the forcipules may appear as two small, V-shaped indentations on the skin. These localized symptoms typically resolve on their own within a few hours to a couple of days.
If a bite occurs, thoroughly clean the affected area with soap and water to prevent secondary infection. Applying a wrapped cold compress or ice pack can help reduce swelling and alleviate the localized pain. While severe reactions are uncommon, medical attention is warranted if signs of an allergic reaction develop, such as difficulty breathing, widespread hives, or swelling of the throat. A consultation with a medical professional is also advisable if the pain is extreme, symptoms worsen, or signs of infection appear after 48 hours.
Typical Habitats and Home Entry Points
Centipedes thrive in environments that offer darkness, moisture, and shelter. Outdoors, they fulfill an ecological role as predators in damp areas like under decaying logs, beneath rocks, within leaf litter, and in garden soil. The prevalence of moist coastal areas, particularly west of the Cascade Mountains, supports substantial populations of these moisture-dependent arthropods.
Centipedes enter homes primarily when seeking refuge from drying outdoor conditions or in pursuit of indoor prey. They favor dark, damp locations, including basements, crawl spaces, garages, and bathrooms, where humidity levels are highest. Common entry points include cracks and gaps in the foundation, unsealed utility openings around pipes, and poorly fitting doors or windows. Reducing moisture indoors and sealing exterior access points can limit the likelihood of an unexpected encounter.