Get Ready to Get Itchy: A “Mosquito Surge” Is Hitting the California Mountains

With the Sierra’s record snowpack beginning to melt, swarms of the biting insects are coming out en masse. For hikers, that could be a nuisance.

Photo: Paul Starosta

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Hiking in California’s Sierra is about to get a little bit less comfortable, and a lot more itchy, due to the emergence of “snowmelt mosquitoes.” A spike in temperature paired with high Sierra snowpack is causing swarms of mosquitoes to hatch at the same time, leading to an atypical bug season. 

In a normal year, mosquitoes hatch gradually throughout the season, creating a relatively even distribution of insects. But due to this season’s snowpack, still water, and unseasonably warm temperatures, the mosquitoes are hatching en masse right now. 

Joel Buettner, the general manager of the Placer Mosquito and Vector Control District, told California’s KRCA that the area “went from no mosquitoes because they were under snow to mosquitoes hatching.” The Placer Mosquito and Vector control District uses a number of different strategies to monitor and manage mosquito activity including the use of drones, and is currently noticing a surge of mosquito activity.

As the snow melts, standing water is becoming more prevalent across the Sierra, which could be enhancing the mosquito population. 

“The difference and concern (this season) is the timing. If it stays over 100 for a month, we’ll see a tremendous increase. Basically, from zero to one hundred [percent] of mosquito production,” said Buettner.

While mosquito swarms are currently worse than usual, officials aren’t yet sure if the number of mosquitoes is going to be higher this year. Buettner notes that a spike in mosquito activity isn’t uncommon in these parts of the state, but it usually happens earlier in the season and with less gusto. 

Additionally, conditions across the Sierras currently vary widely, with stretches of it still buried under snow. Some portions of the Pacific Crest Trail (PCT) are under attack from snowmelt mosquitoes while regions of the state like Truckee haven’t reported abnormal mosquito activity. 

The surge of “snowmelt mosquitoes” comes just two months after the Orange County Mosquito and Vector Control Unit predicted a heavy mosquito season in an interview with southern California’s ABC 7. Heather Hyland, the director of the OC Vector Control Unit noted that there were more opportunities for mosquitoes to breed this season 

“There’s areas due to the rain that are filling up that are producing more egg laying sites for mosquitos per usual,” she said.

What’s worse is that Aedes mosquitoes are among the most active breeds this season, and they’re known for “ankle biting,” and exhibiting aggressive behavior. 

California’s Department of Public Health suggests that this season’s mosquito population is likely to continue expanding. As a result, PCT hikers and other Sierra adventurers may be more likely to struggle with mosquito mobs over the coming weeks. 

Mosquitoes aren’t just a nuisance, they’re also known to carry diseases like dengue fever, the West Nile virus, and malaria. To manage mosquito activity, the CDC recommends using insect repellents like DEET and picaridin and insecticide like permethrin to deter mosquitoes from making contact with skin and clothing.

From 2023