Twenty-four mosquito species in six genera occur in Lake County. Each mosquito has its own preferred larval habitat, season, and blood meal hosts. Mosquitoes undergo complete metamorphosis: egg, larvae, pupae, and adult. The first three mosquito life cycle of these stages are spent in the water.
Depending on the species mosquito eggs are laid singly or in rafts either on the water’s surface or on something solid that will eventually be under water. A female mosquito deposits 50 - 200 eggs. In the summer, the eggs can hatch into larvae in 2-3 days. Only unmoving water with organic material can support developing mosquito larvae, so females lay their eggs in tree holes that fill with rain water, tide water pools in salt marshes, sewage effluent ponds, irrigated pastures, rain water ponds, and horse troughs. Mosquitoes will also lay eggs in “backyard habitats” like unmaintained swimming pools and water features. Any container that holds water continually for a week may be a suitable habitat for a female to lay her eggs, even pet water dishes and overflow reservoirs beneath potted plants.
Larvae grow through 4 instars or stages, shedding their hard outer skin each molt so the larvae can grow to the next stage. Larvae breathe air through a tube called a siphon that pokes through the water’s surface. They have a well-developed head with mouth brushes that filter algae, bacteria, and other microorganisms out of the water. The larval stage lasts between 4-14 days depending on water temperature and mosquito species. After growing to a 4th instar, the larva transforms into a pupa.
The pupal stage for a mosquito is the equivalent of the cocoon stage for a butterfly; this is where the larval mosquito transforms into an adult mosquito. Pupae do not grow so they do not eat. They breathe through a pair of siphon tubes at the water surface similar to the larvae. Once development is complete, the adult mosquito emerges from the pupal case.
Three days after a female mosquito emerges from the pupal case she is ready to take a blood meal. It takes about three days, depending on temperature, for the blood meal to be digested and eggs to develop. Male mosquitoes do not take blood because they do not need to produce eggs. Because they need energy for flight and other activities, both male and female mosquitoes feed on plant nectar and other sugar sources. During summer, mosquitoes complete a full metamorphosis (from egg to adult), in approximately 7-10 days. If you add the approximately three days it takes of the female to harden and find a host and the three days it takes for eggs to develop, the time from egg-to-egg is approximately two weeks.
Mosquitoes of Lake County
|Scientific Name||Common Name|
|Aedes bicristatus||Snowpool mosquito|
|Aedes fitchii||Snowpool mosquito|
|Aedes increpitus||Snowpool mosquito|
|Aedes melanimon||Irrigated pasture mosquito|
|Aedes nigromaculis||Irrigated pasture mosquito|
|Aedes sierrensis||Western treehole mosquito|
|Aedes vexans||Inland floodwater mosquito|
|Anopheles franciscanus||No common name|
|Anopheles feeborni||Western malaria mosquito|
|Anopheles occidentalis||No common name|
|Anopheles punctipennis||Woodland malaria mosquito|
|Culex apicalis||No common name|
|Culex boharti||Bohart's mosquito|
|Culex erythrothorax||Tule mosquito|
|Culex pipiens||Northern house mosquito|
|Culex stigmatosoma||Banded foul water mosquito|
|Culex tarsalis||Western encephalitis mosquito|
|Culex territans||No common name|
|Culex thriambus||No common name|
|Culiseta incidens||Cool weather mosquito|
|Culiseta inornata||Large winter mosquito|
|Culiseta particeps||No common name|
|Orthopodomyia signifera||White-lined mosquito|
|Coquillettidia perturbans||Cattail mosquito|
Invasive Aedes mosquitoes
Two invasive mosquito species, Aedes aegypti (yellow fever mosquito) and Aedes albopictus (Asian tiger mosquito), have become established in California in recent years.
As of July 2017, neither Aedes aegypti (yellow fever mosquito) nor Aedes albopictus (Asian tiger mosquito) has been detected in Lake County. The District’s surveillance program includes methods that specifically target these two species.
The two species share many similarities; both
- are small, black-and-white mosquitoes
- bite aggressively during the day, especially in shaded areas of the yard
- lay eggs in containers (like buckets, roof gutters, used tires, wheelbarrows, children’s toys, canoes and other boats stored in yards, tarps, and other common backyard containers)
- have eggs that can remain dry for years and hatch when flooded
- can transmit Zika, dengue, chikungunya, West Nile, and other viruses.
More information about these invasive mosquitoes, including a map that shows their current range in California, is available from the California Department of Public Health’s Aedes aegypti (yellow fever mosquito) and Aedes albopictus (Asian tiger mosquito) page https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/Aedes-aegypti-and-Aedes-albopictus-mosquitoes.aspx
Class Arachnida: Order Acari
Ticks are a well known and widely despised group of organisms. They are easily recognized by their single body segment and eight legs. All ticks are parasites and must feed on blood to grow and reproduce. Some ticks vector viruses, bacteria, and even protozoans; that is, they are capable of transmitting disease-causing agents from one host to another as they feed. There are actually two groups, or families, of ticks: the hard ticks (the kind that you pull off of your dog) and the soft ticks (which you have probably never seen). They differ in a number of ways including appearance, the method of attaining a host, and the number of life stages.
Family Ixodidae: The Hard Ticks
California’s varied habitats are home to 31 species of hard ticks. These ticks have four life stages: egg, two sub-adult stages (larva and nymph), and adult. Both sub-adults and adults may be found in grass, brush, leaf litter, on tree trunks and rocks. Hard ticks are exposed in the environment in an attempt to hitch a ride on a passing host. The tick climbs on, attaches and feeds for multiple days. A hard tick’s appearance changes drastically as it feeds; what starts off looking smooth and hard becomes swollen and distorted. Adult females gorge on so much blood that they increase in size by as much as ten times. Once a sub-adult feeds, most drop off of the host and molt to the next life stage. A few species of hard ticks remain on a single host, molting and feeding repeatedly. Adults feed once to become sexually potent (males) or to produce eggs (females). In Lake County, three types of hard ticks are commonly encountered by people and outdoor pets. Large images of all three species are available at Tick Encounter, a website maintained by the University of Rhode Island. Additional information about tick ecology and tickborne disease (diseases spread by ticks) may be found at the California Department of Public Health and the Centers for Disease Control.
Western Black-legged Tick (Ixodes pacificus), aka Deer Tick
Western Black-legged adults have dark bodies and, not surprisingly, black legs. This is a cool weather species; adults are usually active from the first fall rains through spring (October through May). Adults feed on a variety of large mammals including deer, horses, people, and dogs. Sub-adults have been collected year-round but are most abundant in the spring. These primarily parasitize western fence and alligator lizards, ground foraging birds and small rodents but will also feed on larger hosts including people. This tick is commonly collected in chaparral and mixed oak woodlands in Lake County.
The Western Black-legged Tick is the primary vector of Borrelia burgdorferi (the bacteria that causes Lyme disease) in the western United States. The Centers for Disease Control (CDC) report that Lyme disease is the most commonly reported vectorborne disease (those that are spread by ticks and insects) in the nation. Reports of illness are comparatively high in the northeast relative to the west. Both adults and nymphs may be vectors of the disease and infection rates vary significantly by location and year. In 2013, nymphs collected in Lake County had infection rates ranging from approximately three to nine percent.
Pacific Coast Tick (Dermacentor occidentalis), aka Dog Tick
Adults of the Pacific Coast Tick are brown with off-white mottling across tick collecting the male’s entire back and a portion of the female’s. The Latin word “occidentalis” means western, an appropriate name for a tick which is only found in Oregon, California, northern Baja California, and Mexico. Adults have been collected in California year-round but are most abundant in the spring. Among adult hosts are deer, cattle, horses, and man. Sub-adults are most abundant in spring and summer and feed primarily on rodents, especially squirrels. In Lake County, adults of this species are commonly collected in the same habitats as the Western Black-legged Tick.
The Pacific Coast Tick has been found naturally infected with a virus and multiple bacteria that cause disease in humans: among these is the bacterium Rickettsia 364D. The first human infection with this pathogen was reported in Lake County in 2008 (Shapiro et al. 2010).
American Dog Tick (Dermacentor variabilis), aka Dog Tick
Female American Dog Ticks are very similar to female Pacific Coast Ticks. It is fairly easy to tell the males apart; the former have more distinctive whitish markings than the latter. American Dog Ticks are found throughout much of the United States and have also been collected in Canada and Mexico. In Lake County, adults are rarely collected in chaparral where Western Black-legged and Pacific Coast Ticks are abundant. They can be found in large numbers in sunny, grassy habitats particularly those near waterways. Adults have been collected in California throughout the year but are most active March through July. They commonly feed on dogs and people as well as a variety of carnivorous hosts. Sub-adults feed on rodents and rabbits.
The American Dog Tick is an important vector of Rocky Mountain spotted fever and also transmits the bacteria that cause tularemia. A bite from this tick may cause tick paralysis.
Family Argasidae: The Soft Ticks
Soft ticks are irregular in shape and textured in appearance which makes them well-camouflaged. These are odd-looking creatures; not unlike a clump of dirt with legs. Soft ticks hide until a host lays down nearby, then rush out to feed. These fast-moving ticks typically feed for 30-60 minutes at a time. Soft ticks have between nine and twelve life stages: egg, larva, six to nine nymphal stages, and adult. Because these ticks feed quickly they grow incrementally. Mature females feed repeatedly and produce many small batches of eggs during their life. There is only one soft tick commonly found in Lake County.
Pajahuello Tick (Ornithodorus coriaceus)
The Pajahuello Tick is found near resting places of its large mammalian hosts (primarily deer and cattle) but will readily take blood from almost any warm-blooded animal. Although many people will never encounter this tick, the likelihood of exposure increases if you come in contact with host bedding sites, (ie. deer beds) during activities such as hiking, hunting or camping. For humans, the bite of this tick is notoriously painful and may result in a localized inflammatory response due to a toxic substance introduced into the bite site during feeding. This tick is not known to vector disease to people.
Other Biting Flies
Snipe Flies, Symphoromyia spp.
There are two species of snipe fly known from Lake County. Little is known about their biology, but they are not a serious biting problem for people in the County. They have a characteristic "stiletto-shaped" body, and are orange or gray in color.
Black Flies, "Buffalo gnats"
Family Simuliidaeblack fly
There are 9 black fly species known from Lake County. Most develop in clean, clear, fast-moving streams. The females dive into the water to glue their eggs to rocks or underwater plants. The larvae develop here, and pupate underwater; the adults emerge a few weeks to months later. Females bite a variety of mammals and birds, but the species present in Lake County rarely bite people.
Horse Flies & Deer Flies
There are 19 species of tabanids known from Lake County. These are large, day-flying insects best known for their painful bites. Although their common names suggest that they feed on horses and deer, our local species feed on a variety of hosts, including man, cattle, and a few are not known to bite at all! In all cases, only the females bite, and they use the protein from bloodmeals for their eggs. The larvae (maggots) of most deer and horse flies are found in aquatic or semi-aquatic habitats (streams and ponds, or the muddy/sandy soils along the shore). The larave are largely predaceous on other insects.
no-see-ums, punkies, biting gnats, biting black gnats
This is a diverse group of tiny flies. Larvae are predaceous or feed on decaying organic matter, while many of the adults have the unfortunate habit of feeding on blood. Their bites are often painful, and may leave large, itchy welts. The larvae develop in moist or wet substrates (such as mud or wet treeholes) and are usually predaceaous upon other insects. Twenty-nine species are known from Lake County.
Kissing Bugs, "Conenose bug", Triatoma protracta
Order Hemiptera: Family Reduviidae
Triatoma protracta lives in the nests of wood rats (Neotoma spp.), but adults sometimes fly into homes and may feed on people. The immature stages (nymphs) lack wings and are limited to crawling. Nymphs rarely occur in homes, but their presence may indicate that a wood rat nest is present under the building. Their bites are not usually painful, but some individuals are kissing bug very sensitive to their bites and can have life-threatening allergic reactions. In Latin America these insects are important because they sometimes carry a protozoan, Trypanosoma cruzi, which causes Chagas' disease in humans. This debilitating disease is rare in the United States, however, with only two recorded cases in southern Texas and one in central California.
West Nile, Zika & Other Viruses
West Nile Virus (WNV)
What is WNV?
West Nile virus (WNV) is a mosquito-borne disease that was originally found in Africa. In 1999, it was detected in the eastern United States; since then the virus has spread throughout the United States and is well established in most states, including California.
How do people contract WNV?
- Infected mosquitoes: Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers ("vectors") that become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite.
- Transfusions, transplants, and mother-to-child: All donated blood is checked for WNV before being used. The risk of getting WNV through blood transfusions and organ transplants is very small, and should not prevent people who need surgery from having it. Transmission during pregnancy from mother to baby or transmission to an infant via breastfeeding is extremely rare.
- Not through touching: WNV is not spread through casual contact such as touching or kissing a person with the virus, or by breathing in the virus.
How soon do infected people get sick?
People typically develop symptoms from 3 to14 days after they are bitten by an infected mosquito.
What are the symptoms of WNV?
- Serious Symptoms in a Few People. Less than one percent (about 1 in 150 people) of individuals infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, paralysis, and death. These symptoms may last several weeks, and neurological effects may be permanent.
- Milder Symptoms in Some People. Up to 20 percent (about 1 in 5) of the people who become infected will display symptoms which can include fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms generally last for just a few days, although even previously healthy people have been sick for several weeks.
- No Symptoms in Most People. Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms.
Who is at the greatest risk of getting severely ill from WNV?
- People over the age of 50 have a higher chance of getting sick and are more likely to develop serious symptoms when infected with WNV.
- Being outside, especially at dawn or at dusk, increases your risk of being bitten by an infected mosquito. Take precautions to avoid mosquito bites if you spend a lot of time outside, either working or playing.
- Risk of transmission through medical procedures is very low. All donated blood is checked for WNV before being used. The risk of getting WNV through blood transfusions and organ transplants is very small, and should not prevent people who need surgery from having it.
How is WNV infection treated?
There is no specific treatment for WNV infection. In cases with milder symptoms, people experience fever and aches that pass on their own. In more severe cases, people may need to go to the hospital where they can receive supportive care including intravenous fluids, help with breathing, and nursing care.
If you have had WNV, are you immune to further infections?
It is thought that once a person has recovered from WNV, they are immune for life to future infections with WNV. This immunity may decrease over time or with health conditions that compromise the immune system.
Can animals get sick with WNV?
An infected mosquito can bite any animal, but not all animals will become sick. The disease most often affects birds but may occasionally cause disease in other animals.
- Wild birds serve as the main source of virus for mosquitoes. Infection has been reported in more than 225 bird species. Although many birds that are infected with WNV will not appear ill, WNV infection can cause serious illness and death in some birds. The most severe illnesses are seen among the corvid birds, which include crows, jays, ravens, and magpies.
- Squirrels & Rabbits with West Nile virus can develop neurological symptoms such as uncoordinated movement, paralysis, shaking, or circling and may die.
- Like people, most horses bitten by mosquitoes will not become sick with WNV. However, of those that do, clinical signs may include stumbling, circling, hind leg weakness, inability to stand, muscle tremors, and death. A vaccine to prevent West Nile virus is available for horses and horse-owners should consult with a veterinarian about vaccinations for WNV and other mosquito-borne viruses, such as western equine encephalomyelitis. For more information on West Nile Virus and horses, please visit the California Department of Food and Agriculture.
- Dogs and cats can be exposed to WNV in the same way as humans. However, these animals are very resistant to WNV and rarely become ill. Concerned pet owners should consult with a veterinarian.
Zika virus was first reported in the Western hemisphere from Brazil in March 2015. Zika virus is spread to people primarily through the bite of an infected Aedes aegypti (yellow fever mosquito) or Aedes albopictus (Asian tiger mosquito) mosquito [Can we link this to the section on invasive Aedes?]. It is also possible for a pregnant woman to pass Zika to her fetus during pregnancy or around the time of birth, and a person infected with Zika can pass it to his or her sex partners. Many people infected with Zika will have no symptoms or mild symptoms that last several days to a week. However, Zika infection during pregnancy can cause a serious birth defect called microcephaly and other severe fetal brain defects. Current research suggests that Guillain-Barre syndrome (GBS), an uncommon sickness of the nervous system, is strongly associated with Zika; however, only a small proportion of people with recent Zika virus infection get GBS. Once someone has been infected with Zika, it is likely he will be protected from future infections. There is no evidence that past Zika infection poses an increased risk of birth defects in future pregnancies.
For more information, visit
California Department of Public Health Zika Virus page https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/Zika.aspx
CDC Zika Virus page https://www.cdc.gov/zika/index.html
Chikungunya virus is transmitted to humans from the bite of an infected Aedes aegypti (yellow fever mosquito) or Aedes albopictus (Asian tiger mosquito) mosquito [Can we link this to the section on invasive Aedes?]. Other symptoms may include headache, muscle pain, joint swelling, or rash. In 2013, chikungunya virus was found for the first time in the Americas on islands in the Caribbean. Locally-acquired cases were detected in Florida, Puerto Rico, and the US Virgin Islands in 2014.
California Department of Public Health Chikungunya Virus page https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/Chikungunya.aspx
CDC Chikungunya Virus page https://www.cdc.gov/chikungunya/index.html
Dengue is a mosquito-borne disease caused by four closely related viruses known as dengue virus-1, -2, -3, and -4. Dengue virus is transmitted to humans from the bite of an infected Aedes aegypti (yellow fever mosquito) or Aedes albopictus (Asian tiger mosquito) mosquito [Can we link this to the section on invasive Aedes?]. The symptoms of dengue fever are high fever, severe headache, severe pain behind the eyes, joint pain, muscle and bone pain, rash, and mild bleeding (e.g., nose or gums bleed, easy bruising). Locally acquired dengue is uncommon in most of the United States, but in recent years, locally acquired cases have occurred in Florida, Texas, and Hawaii. Dengue is endemic in Puerto Rico and the US Virgin Islands, and most of the US-affiliated Pacific Islands.
For more information, visit
California Department of Public Health Dengue Virus page https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/Dengue.aspx
CDC Dengue Virus page https://www.cdc.gov/dengue/index.html
St. Louis Encephalitis Virus
Prior to the introduction of West Nile virus, St. Louis encephalitis (SLE) virus had the greatest medical importance of the mosquito-borne diseases in North America. SLE virus was first recognized in 1933 in St. Louis, Missouri, and epidemics have occurred sporadically and unpredictably in the subsequent decades. Symptoms usually appear abruptly, and may include fever, headache, dizziness, nausea, and malaise; more severe symptoms may develop, including stiff neck, confusion, disorientation, dizziness, tremors and unsteadiness. Like West Nile virus, SLE virus is maintained in a mosquito-bird-mosquito cycle, but no major SLE outbreaks have occurred since WNV arrived in the Americas.
California Department of Public Health St. Louis Encephalitis Virus page https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/SLE.aspx
CDC St. Louis Encephalitis Virus page https://www.cdc.gov/sle/
Dog or canine heartworm (Dirofilaria immitis) disease is increasingly prevalent in domestic dogs and wild canids (i.e. coyotes). Dog heartworm is endemic to Lake County where it is transmitted by mosquito vectors. This filarial nematode (roundworm) causes severe circulatory disease in dogs and coyotes, but also can dog heartworm cause respiratory disease in humans. Mosquitoes become infected by ingesting very small infective stages of the worm (microfilaria) while feeding on an infected dog. In the mosquito, the worm molts twice and moves to the mouthparts where they remain until the mosquito refeeds. During blood feeding, the worms move out of the proboscis and into the bite wound. In dogs and other canines, the worms molt to the adult stage and migrate to the large blood vessels and heart where mating and reproduction occur. Disease in dogs occurs when the number of worms becomes sufficiently large enough to impede blood flow and heart function. In humans, immature worms frequently become encapsulated in the lungs where they are detectable by chest x-ray.