Skip to content

A biblical plague or a winged love story? The truth about California’s annual termite swarms

Autumn rains bring annual termite swarms in Redwood City
Reproductive swarms of Reticulitermes, a genus of termites endemic to North America

As the first autumn rainfall hit Redwood City this weekend, another ecological event has caught the attention of local residents. A day after the first precipitation, swarms of flying termites were seen emerging, seemingly, from out of the blue.

So, are the rains really triggering an early autumn termite explosion?

“Absolutely,” said Andrew Sutherland, the Urban Integrated Pest Management Advisor for the San Francisco Bay Area. “Most likely what’s being observed are swarms of western subterranean termites.”

According to Sutherland, these events happen once or twice a year, depending on the region, with autumn swarms being more common in the Bay Area. And, despite their resemblance to a biblical plague, they’re actually more of a regional romance.

“Since they live underground, they have to have opportunities to meet and fall in love,” said Sutherland. “So it's kind of like a big singles bar in the air.”

As social insects, termites reside in large, communal colonies ranging from a few hundred to a few million individuals. Sutherland said they rely on these annual “nuptial swarms,” which are a time for the “reproductive members of the colony to leave, find a mate and start their own colony.”

These nuptial swarms are usually a single event that, as residents have observed, occurs on a calm, sunny day following the first autumn rain. When the conditions are right, all the winged virgins, or “alates,” who’ve been waiting near the surface of their colony, exit en masse in search of a mate from a different colony. Unlike bees and ants, however, termites pair up for life. 

“The king and queen form what's called a nuptial pair,” Sutherland said. “And that nuptial pair starts a colony, usually in a piece of wood that is partially buried in the soil.”

Not every pair successfully starts a new colony—some are eaten or fail to find a suitable location—but these huge swarms have the potential to create thousands of new termite settlements.

As for why the rain triggers their pilgrimage, Sutherland suspects it has something to do with the effect of the moisture in softening the earth.

“I would guess it’s because the moisture makes it easier for them to excavate their nuptial chamber,” he said. In other words, wet soil and wet wood is easier to dig through and consume.

“Because we have a Mediterranean climate, this is the beginning of the wet season, which means they'll have more access to soil moisture in the coming months.” 

Rather than destructive pests, however, Sutherland said termites are, for the most part, peaceful co-habitants and vital ecosystem engineers.

“These are native insects, so they were here before us,” he said. “And they often can be living alongside us without threatening our homes.”

Because much of the South Bay was built on top of orchards, he added, there’s an abundance of dead roots and trunks underground that are ideal food and lodging for termite colonies. So not only are the insects taking up residence in these underground environments, but they’re also helping shape and nourish them.

“They are incredible decomposers of plant material,” said Sutherland. He said that termites can remove up to a third of the dead wood and leaves that fall every year in some ecosystems. This helps with soil turnover, as well as loosening the ground to facilitate water infiltration. On top of this, termites are an essential food source for birds, lizards, and other species. Sutherland described their nuptial swarms as “a buffet.”

For those still panicked about the thousands of termites setting up shop on their property, Sutherland said that most modern homes were built to prevent infestation. Local building codes prevent wood from coming into direct contact with the soil, making it difficult for termites to burrow from their underground colonies to the house foundation. 

“We've had lots of observations where we have large termite colonies in somebody's yard, all the way up to adjacent to the house, but the house never becomes infested,” he said.

Still, he recommends a regular inspection every three to five years, just in case.

“That's all you can do for prevention,” he said. “This is a very, very common native insect, it's everywhere. So chances are they’re already in your backyard.”

For more information about pest management and ongoing search see the University of California Integrated Pest Management Program’s Subterranean Termites Pest Notes, a research-based guide to pest management for termites in California, and the UC Agriculture and Natural Resources blog article about Andrew Sutherland’s research project studying spring vs autumn swarming termites.


Leah Worthington is the lead reporter at the Redwood City Pulse, a local news site dedicated to providing accurate and timely news to the Redwood City community. Leah can be reached at, on Twitter, and by phone at 650-888-3794. To read more stories about Redwood City, subscribe to our daily Express newsletter on


Leah Worthington

About the Author: Leah Worthington

Leah, a Menlo Park native, joined the Redwood City Pulse in 2021. She covers everything from education and climate to housing and city government. Previously she worked as the online editor for California magazine in Berkeley and co-hosts a podcast.
Read more
push icon
Be the first to read breaking stories. Enable push notifications on your device. Disable anytime.
No thanks