Mosquitoes of Clark County

There are over 3,500 species of mosquitoes found throughout the world, and of the 40+ species found in Washington state, Clark County is home to 19 established species of mosquitoes. These local species are considered nuisance mosquitoes, meaning that they bite humans as well as animals. Some of these established species can vector diseases, though it should be noted that there have been zero known positive cases of locally acquired mosquito-borne zoonotic disease transmission to humans in Clark County. Mosquitoes have different feeding preferences. While some mosquitoes are persistent and painful biters, some mosquito species will leave humans alone altogether, preferring instead to feed on birds, large mammals, snakes, or even frogs. All of the established Clark County mosquito species fall into five genera, or groups of closely related species.

Aedes are one of the most common groups of mosquitoes in the state of Washington, and account for the majority of mosquitoes in Clark County. Some species of Aedes are strictly a nuisance, while others can potentially vector diseases to humans and animals. Locally, this group of mosquitoes are most active from June through August. Their ideal breeding habitats largely consist of snow melt pools, temporary pools of water, flood water, irrigation water, tree holes, and artificial containers. The females will lay their eggs singly on the ground or above the water level in an object that can hold water. Aedes mosquitoes typically overwinter as eggs or larvae, rather than as adults. As adults, Aedes primarily feed on humans, with their peak activity usually around dawn and dusk, though they may also bite during the day in shaded areas. While their lifespan can vary greatly among species, the typical lifespan for adult Aedes mosquitoes in nature is about two weeks. The lifespan for Ae. vexans in Clark County may be closer to four weeks. Since 2022, Clark County has observed Ae. vexans activity periods lasting around eight weeks. While currently rare in Clark County, Aedes can transmit Avian Malaria and Canine Heartworm. Internationally, certain species of Aedes mosquitoes transmit Chikungunya, Dengue, Yellow Fever, and Zika viruses; for more information, please visit our Mosquitoes and Diseases page.

The following species of Aedes are considered established in Clark County: Ae. cinereus, Ae. excrucians, Ae. fitchii, Ae. increpitus, Ae. j. japonicus, Ae. sierrensis, Ae. sticticus, and Ae. vexans.

The following species of Aedes have been found in Clark County, but are not considered established: Ae. aboriginis, Ae. intrudens, Ae. s. idahoensis, Ae. togoi, and  Ae. ventrovittis.

The ideal breeding habitat for Anopheles mosquitoes include: water seepages with vegetation, derelict pools, and stagnant water in either the sun or shade. Females will lay their eggs singly on the water, where they will float until they hatch as larva. Anopheles larvae can be easily identified in the field as they will lie horizontally on the water surface to breathe. This behavior is unlike the larvae of other genera, which usually lie diagonal to the water surface. Female Anopheles mosquitoes will overwinter as adults. These mosquitoes typically feed at dawn, dusk, and during the nighttime. Historically, this group of mosquitoes are most active during the month of August in Clark County. They primarily feed on mammals, including humans. Anopheles can transmit Canine Heartworm and An. freeborni can transmit Malaria. For more information, please visit our Mosquitoes and Diseases page.

The following species of Anopheles are considered established in Clark County: An. freeborni and An. punctipennis.

The following species of Anopheles have been found in Clark County, but are not considered established: An. occidentalis.

Clark County has one established species of Coquillettidia mosquitoes, Coquillettidia perturbans, also known as the “cattail mosquito.” Their ideal breeding habitats are typically pools of permanent freshwater with emergent vegetation, such as freshwater marshes. They have been locally found in marshes, bioswales, and other bodies of water that all contain cattails, reeds, or similar aquatic vegetation. Like Culex and Culiseta mosquitoes, female Coquillettidia will lay their eggs in rafts on the surface of water. Unlike other mosquito larvae and pupae, Coquillettidia species remain entirely below the water surface during the first three stages of their development. They achieve this by using specialized serrated siphons, or respiratory “trumpets,” to penetrate and attach themselves to either the roots or hollow stalk of an aquatic plant, from which they obtain their oxygen. The lifespan of adult Coquillettidia mosquitoes typically range from one to two months. In Clark County, Cq. perturbans are historically active in July. This species prefers to feed on birds, but has been known to feed on horses, humans, and other mammals.

The following species of Coquillettidia are considered established in Clark County: Cq. perturbans.

Culex mosquitoes make up the second largest group of mosquitoes established in Clark County. They are commonly found around urban areas associated with people, such as towns and cities. Their breeding habitats include stagnant water, flooded fields, and polluted water in catch basins, ponds, or artificial containers. Locally, this group of mosquitoes are most active from June through mid-September. As adults, female Culex mosquitoes will their eggs on the water’s surface in a raft. These egg rafts can hold as many as 300 eggs. Under warm conditions, Culex mosquitoes can undergo their entire development cycle in about 10 to 14 days. Depending on distribution and host-availability, Cx. pipiens and Cx. tarsalis mosquitoes primarily feed on birds and mammals, while Cx. territans primarily feed on amphibians and reptiles, such as frogs and toads. Cx. pipiens and Cx. tarsalis are known to be vectors of West Nile Virus and St. Louis Encephalitis. Cx. tarsalis is the primary vector for Western Equine Encephalitis. Culex mosquitoes are also known to transmit Avian Malaria and Canine Heartworm. For more information, please visit our Mosquitoes and Diseases page.

The following species of Culex are considered established in Clark County: Cx. pipiens, Cx. tarsalis, and Cx. territans.

Culiseta mosquitoes, commonly referred to as “cool weather mosquitoes”, tend to be larger in size than other mosquitoes, particularly Cs. incidens, Cs. particeps, and Cs. inornata species. The ideal prey for this group includes a variety of vertebrates, such as livestock, birds, rodents, reptiles, and humans. These mosquitoes are most active through the months of July to September in Clark County. Their breeding habitats include clean water in ponds, artificial containers, headboxes, and similar environments. Like Culex and Coquillettidia species of mosquitoes, Culiseta will their eggs directly on the water surface and form an egg raft until they develop into larvae. During the winter season, female Culiseta will hibernate as an adult before remerging in the spring to breed.

The following species of Culiseta are considered established in Clark County: Cs. impatiens, Cs. incidens, Cs. inornata, Cs. minnesotae, Cs. morsitans, and Cs. particeps.