Are there mosquitoes in Yosemite?

As with any trip into the Sierra Nevada, it's possible (though unlikely) while visiting Yosemite that you could be exposed to a variety of vector-borne diseases. Here are some general tips to reduce your risk: Avoid contact with mosquitoes and ticks.



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Many mosquitoes are most active at dusk and dawn, mainly during the summer. Be sure to use insect repellent and wear long sleeves and pants or consider staying indoors during these hours.

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If you are into light activity and sightseeing, a medium-weight jacket over layers will suffice. Just in case, bring a hat and gloves to ward off the night chill. Day hikers or treaded walking shoes are necessary whether you are walking a valley trail on a ranger-led hike or heading up steeper trails.

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Most years, the majority of bears in Yosemite begin closing in on a hibernation location starting as early as October.

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About 300-500 black bears live in Yosemite's 750,000 acres. (Grizzly bears no longer live in California.) A black bear's diet consists mainly of berries, grasses, nuts, and insects.

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Stay away from river and creek banks during high water conditions and avoid rock hopping. Stream polished rocks along the water's edge may be slippery when wet or dry. If you choose to cross a stream without a bridge, avoid deep and/or swift water.

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There are only two places in the world that are completely and utterly mosquito-free: Antarctica and Iceland.

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One downside: The year-round waterfalls will still be flowing – waterfalls like Vernal, Nevada, and Bridalveil, but unless it's already rained before you arrive, ephemeral waterfalls like the great Yosemite Falls may be dry or barely a trickle.

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No matter which season you are planning to visit Yosemite, layers will be important. During the spring, summer, or fall, we recommend wearing a base of shorts and a tank top or t-shirt then layering from there. Cargo pants that have removable sections are great.

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While true altitude sickness is normally only the concern of mountaineers heading for high summits, you can experience mild symptoms from the elevation in Yosemite—headaches, shortness-of-breath, and the like—as low as 5,000 feet. Staying a step ahead of altitude sickness means taking things slow.

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Hantavirus pulmonary disease (HPS) is a rare but serious disease that humans can contract through contact with infected rodents or their urine, saliva, blood, or droppings.

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