They're seeing an influx of calls from homeowners with ground nests on their property.
Contra Costa Vector District Control Officials responded to several calls from homeowners in Moraga, Orinda, and Lafayette.
It's not an easy job but Vector Control Aide Heidi Budge arrived prepared for the painstaking task.
She's suited up, ready to treat any Yellow Jacket ground nest she sees.
"This was a pretty active nest. And they were starting to let us know they didn't want us around their nest," said Budge.
Contra Costa County Vector District Control has seen an 83-percent increase in calls from homeowners requesting service for Yellow Jackets.
"Don't try to treat it yourself, it seems like they get more aggressive when you try to treat it with spray or a soapy water concoction," said Budge.
The heavy winter rains and summer heat created just the landscape for Yellow Jackets to thrive.
"They will keep stinging you, unlike a honey bee that loses its stinger and be done, the Yellow Jackets can sting you over and over and over," said Julie Tausend, a Moraga resident.
The insects are showing up in record numbers, as the months get colder. Eventually, they'll die off but right now they're in full swing.