Swarms of dragonflies have descended on California, filling skies and public parks across the San Francisco Bay Area as the insects hunt for food during their summer breeding season.
Onlookers across Northern California have reported seeing hundreds of dragonflies flying overhead, with some of the creatures even mating on top of people's hats in public spaces.
The flying insects have taken over grassy fields, parks, rivers and ponds throughout the region while searching for prey during a critical phase of their life cycle. Entomologists define the period from June through August as peak dragonfly season in the United States, when adult dragonflies emerge from underwater breeding sites to inhabit local meadows and lawns.
High numbers spotted across the Bay Area
In Oakland, squadrons of dragonflies have been sighted flying over grassy hills near Lake Merritt. Further north in Sonoma County, swarms have gathered along the Russian River near Guerneville, while in San Francisco, large groups have clustered around new plant growth at Dolores Park.
Residents across the San Francisco Bay Area, a major metropolitan region surrounding the San Francisco Bay estuary, have observed a noticeable increase in dragonfly activity over recent months.
"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," one Bay Area resident said.
Another local resident shared observations on social media detailing the scale of the insects' presence across popular city spots. "It's the entire region. Washington Square Park has millions right now. Thousands by the Ferry Building this morning. Tons at Golden Gate Park yesterday," the resident claimed.
Weather and food supply fueling swarms
While massive swarms of flying bugs can cause unease among members of the public, experts emphasize that the dragonfly influx provides significant environmental benefits to the West Coast. Dragonflies actively hunt mosquitoes, which serve as their primary food source.
Chris Grinter, senior collection manager of entomology at the California Academy of Sciences in San Francisco, explained the factors driving the population surge. "Cool weather, wind currents, and an abundance of food (mosquitoes) are likely contributing to the high numbers," Grinter told SFGATE.
Adult dragonflies can catch and eat up to 100 mosquitoes in a single day. In their larval stage, dragonfly nymphs act as underwater predators, hunting and consuming mosquito larvae in standing water pools across populated urban areas.
Natural pest control for coastal regions
The arrival of dragonfly season extends beyond California, with newly matured insects emerging from lakes and ponds nationwide. In July 2024, massive dragonfly swarms flew past beachgoers in Rhode Island as the insects migrated to warmer breeding habitats along the East Coast of the United States.
Dragonflies are capable of surviving longer in southern states and along the West Coast, where temperatures typically remain warmer as summer transitions into autumn.
The biological cycle begins in late spring or early summer, sometimes as early as April, immediately after adults emerge from water, reach maturity and mate. Female dragonflies deposit eggs directly into water, or onto mud and plants along local aquatic habitats. These eggs generally hatch within days or weeks, allowing nymphs to develop underwater throughout the cooler months before emerging as full-size adults the following spring and summer.
Peak visibility for flying adult dragonflies occurs between June and August. During these summer months, high population numbers help reduce local pest populations, as dragonflies consume mosquitoes, gnats and other fly species, acting as natural insect repellents for humans.
Physical characteristics and safety
Researchers estimate that around 30 different species of dragonflies inhabit the Bay Area region. These insects can reach flying speeds of up to 35 mph, grow up to five inches in length, and feature wingspans exceeding six inches, giving them a physical profile comparable to a flying ballpoint pen with wings the length of a smartphone.
Despite their imposing size and swift flight, dragonflies pose no threat to humans. The insects do not possess stingers, do not carry venom, and do not view humans as a source of food.
