Massive swarms of dragonflies have descended on California's Bay Area this summer, filling parks and waterfronts with hundreds of the insects, and scientists say the surge is driven by an abundance of mosquitoes.
Residents across San Francisco and Oakland have reported skies thick with dragonflies in recent weeks, with the insects spotted in such numbers that some have been observed mating on top of people's hats. The swarms have appeared at Lake Merritt in Oakland, along the Russian River near Guerneville, and at Dolores Park in San Francisco, the Daily Mail reported.
Chris Grinter, the senior collection manager of entomology at the California Academy of Sciences, pointed to a straightforward explanation for the boom. He told SFGATE:
"Cool weather, wind currents, and an abundance of food (mosquitoes) are likely contributing to the high numbers."
That last factor matters most for anyone tired of slapping mosquitoes on a summer evening. A single adult dragonfly can kill up to 100 mosquitoes in a day. Their larvae do the same work underwater, hunting and eating mosquito larvae in standing water before they ever take flight. The swarms amount to a free, natural pest-control service, no government program required.
Social media posts from Bay Area residents paint a picture of dragonflies blanketing the region's most recognizable public spaces. One resident wrote that Washington Square Park "has millions right now," with "thousands by the Ferry Building this morning" and heavy numbers at Golden Gate Park the day before.
Another resident noted a longer trend.
"I never ever used to see dragonflies. Since the last maybe year or year and a half there are SO MANY all over the city."
Whether that perceived increase reflects a genuine population boom or simply more people paying attention remains an open question. No scientific baseline data comparing current Bay Area dragonfly numbers to historical averages has been published.
Roughly 30 different dragonfly species live in the Bay Area region. The insects can fly at speeds up to 35 miles per hour, grow as long as five inches, and sport wingspans of about six inches. They carry no stingers, produce no venom, and have zero interest in biting people.
Peak dragonfly season in the United States runs from June through August. Adults emerge from underwater breeding grounds each spring and summer after spending the cooler months as aquatic nymphs. Egg-laying can begin as early as April, and the eggs hatch within days or weeks.
California is not the only state to experience dramatic swarms. In July 2024, massive clouds of dragonflies appeared at a Rhode Island beach as the insects migrated toward warmer breeding grounds along the East Coast.
For Bay Area residents accustomed to government agencies spending millions on mosquito abatement programs, the dragonfly surge offers a useful reminder. The natural world sometimes handles a problem more efficiently than any bureaucracy, and at no cost to the taxpayer.
The swarms may look strange overhead, and finding a pair of dragonflies mating on your hat is not everyone's idea of a pleasant afternoon. But the tradeoff is hard to argue with: fewer mosquitoes, no chemicals, and an insect that minds its own business once the hunting is done.
Sometimes the best government response to a problem is the one that never has to happen at all.
