Irked residents across Southern California have recently complained to their vector control districts about an onslaught of mosquito activity, many sporting ankle bites to prove it. Local mosquito experts blame the unseasonable weather pattern and a thriving invasive species for the surge in itchy bites.
Vector control districts in Los Angeles, Orange and Ventura counties have confirmed a significant increase in mosquito activity, which is highly unusual for this time of the year.
Southern California’s mosquito season typically begins in early May, with the insect’s activity tapering off around October. But local officials say the season is getting longer as temperatures stay warmer further into the year.
Between January and February, Orange County saw “five times as many mosquitoes here over the five-year average,” said Brian Brannon, public information officer for Orange County’s Vector Control District.
Some counties have noticed the major increase through their mosquito traps or from calls for service regarding the flying pests. All three counties have gotten more than 50 calls for service when they’ll receive anywhere between five and 10 in a typical year.
Local experts break down what’s causing the flurry of biting insects in the winter.
The perfect storm for mosquito breeding
Mosquitoes need standing water to lay their eggs. Major rainfall in December and early February created ideal breeding conditions, said Susanne Kluh, general manager for the Greater Los Angeles County Vector Control District.
A mosquito’s early life cycle primarily occurs in water until it becomes an adult and can fly away. The entire life cycle commonly lasts up to two weeks. However, weather conditions can shorten the process to four days or prolong it for as long as a month, according to the Environmental Protection Agency.
Unseasonably hot temperatures in January in between rainstorms accelerated the life cycle of mosquitoes in the region and led to an increase in mosquito activity, Kluh said.
“After the rains late last year and then the warm temperatures, [the mosquitoes] were out and about,” Kluh said. “We found them breeding in people’s backyards, and that didn’t happen in prior years, not to this extent.”
This isn’t the first time unusual weather has spawned a mosquito horde in the region during what should be the insect’s offseason.
In September 2023, rain followed by Tropical Storm Hilary established conditions for breeding and the subsequent insect activity in a time when the mosquitoes typically begin to hibernate.
“A tropical weather pattern makes them really active, busy biting, getting blood meals and laying eggs,” said Cary Svoboda, supervisor of Ventura County’s vector control program. “The population really explodes in those kinds of situations.”
An invasive mosquito is the culprit for the bites on your ankle
The two most common types of mosquitoes that inhabit Southern California include the native Culex mosquitoes and the invasive Aedes aegypti.
Culex are more interested in biting birds rather than humans and are California’s primary spreader of West Nile virus. Aedes aegypti zero in on humans and tend to poke multiples times before taking blood.
Kluh, along with representatives from Orange and Ventura counties, said their teams have noticed over the past several years that the Aedes aegypti are adjusting to living in California and growing in population.
These mosquitoes, like the Culex, love wet conditions but they don’t like the cold weather. However, Kluh said she theorizes the Aedes aegypti might not have completely gone into hibernation during the winter and were ready to pounce at the first sign of warm temperatures.
These observations are anecdotal for Los Angeles County, as the department traditionally sets up its mosquito traps at the beginning of March and leaves them out until about after Thanksgiving, Kluh said. During the winter season the department typically takes a break in mosquito surveillance and refurbishes their traps.
“But next year, I think we’re going to set up some scaled-back winter routes to keep an eye on how things are developing,” she said.
What can we expect for the mosquitoes’ peak summer season?
Local vector control department officials say it’s hard to predict what this current mosquito status means for the insect’s peak activity in the summer.
The mosquitoes’ summer activity depends largely on how the spring goes, Svoboda said. He said the insect’s activity will depend on the amount of rainfall, warm temperatures or even tropical weather that can occur during the spring.
How to stave off mosquitoes
Local officials say the best way to keep mosquitoes at bay is to get rid of any kind of standing water on your property where they can breed.
Even the smallest amount of standing water, for example in a bottle cap, is enough space for Aedes aegypti to lay eggs, Brannon said.
Even though most of the moisture from the recent rains has begun to dry up, experts say, it doesn’t hurt to apply insect repellent when outdoors.
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