Aggressive yellowjackets reported in Contra Costa County

(KRON) — Hundreds of yellowjacket nests around Contra Costa County have been reported to vector control officials as the area experiences a yellowjacket population surge this summer.

More than 700 nests of ground-nesting yellowjackets have been reported to the Contra Costa Mosquito and Vector Control District in 2025. The stinging wasps “will defend their nests aggressively. Contra Costa County residents often encounter the nests by accident, resulting in a painful encounter,” CCMVCD wrote.

Yellowjackets will sting and bite, resulting in a painful welt. Unlike bees, they can sting more than once, vector officials said. When their nest is disturbed, yellowjackets will swarm out and attack the offender, officials said.

“The pain from those bites and stings is real, and for someone who is allergic, the bites and stings can be dangerous,” CCMVCD wrote.

Contra Costa County is home to four common species of yellowjackets: two build their nests in trees or on structures, and two build their nests underground.

“Because ground-nesting yellowjackets build their nests underground in abandoned rodent holes and other voids in the ground, they can be right under your feet,” vector district officials warn.

Residents can make a service request for the district to eradicate a ground-nesting yellowjacket nest. Residents who find a problematic nest should leave a marker near it to let the district’s technician know where to find it.

“Our state-certified technician will come out to confirm the insects are yellowjackets, and once confirmed, the technician will treat the nest. In order for a district employee to treat the nest, the nest must be dry, so please turn off the sprinklers and do not try to treat the nest yourself,” CCMVCD wrote.

According to Contra Costa Mosquito and Vector Control District, here are other things you can do to reduce the risk of ground-nesting yellowjackets on your property:

• Set up yellowjacket traps away from your yard with an attractant to lure the yellowjackets away from you.

• Remove piles of leaves from your yard to eliminate potential shelter for yellowjackets.

• Store wood and lumber piles at least 1-foot above the ground and away from structures.

• Tightly cover garbage containers and recycling bins.

• Do not leave dog or cat food outside.