Aggressive yellowjacket populations are booming this year in the Bay Area as reports of complaints about nests hit records in some areas.
Winter rains produced plenty of insects to eat, which helped wasp nests thrive, insect experts say. Hot September weather — like the Labor Day heat wave — spurred the insects to hunt more aggressively for food, increasing the opportunities for human encounters of a painful kind.
Vector control districts in Santa Clara and Alameda reported an unusually high number of public calls about yellowjackets, and San Mateo County has already set a record for most service requests in a year.
Contra Costa County is on pace to break its all-time high for yellowjacket service requests of 972 set in 1999.
Public calls for help with yellowjackets have increased 83 percent in Contra Costa County so far this year. The vector district received 858 calls through Labor Day this year, up from 469 at the same time last year and more than the 744 calls during all of 2016, the district reported.
Lisa Hallahan, an Orinda resident for two decades, was stung a week ago in her side yard after carefully turning on a water hose faucet near where yellowjackets built a nest in the ground near some of her rose bushes.
“It was a very painful sting,” she said. “I tried to leave them alone and live with them, but I still have some swelling from that sting.”
Alameda County received more yellowjacket calls in July and August than perhaps ever before for that time of year, the county vector control district said.
“Last year we set records, and we’re breaking that record this year,” said Daniel Wilson, a spokesman for the Alameda County Vector Control District. “The activity has really taken off with the hot temperatures in late summer”
Both Contra Costa and Alameda County will poison ground nests at private homes if requested to do so.
Santa Clara County’s Vector Control District doesn’t treat nests on private property, but it is getting a heavy volume of calls to treat nests on public properties such as road medians and parks.
“About every creature that is dependent on rain is more abundant this year, from mosquitoes to rats and mice and yellowjackets,” said Russ Parman, the vector district’s assistant general manager.
The 228 yellowjacket calls in Santa Clara County so far this year are more than any year for which records are readily available, Parman said, and the calls keep coming in..
Santa Clara County’s district had 188 yellowjacket and wasp service requests in July and August, two and a half times more than the 76 calls during those two months in 2016.
San Mateo County’s vector district has had 745 service request this year, a figure district officials believe is an all-time record. The district had 501 calls during all of 2016, said Megan Sebay, a spokeswoman for the San Mateo County Mosquito and Vector Control District
Heidi Budge, a Contra Costa vector control aide, said her agency has had more yellowjacket calls this year than any of her eight years working there.
Contra Costa’s hot spots for problems are Orinda, Lafayette and Moraga, communities with mature landscaping in big yards and plenty of wild trees, brush and plants in open space areas to provide insects for the wasps to feed on and animal burrows for them to take over as nest sites.
On Wednesday morning, Budge suited up in a thick white cotton bee suit with a sturdy hat and netting before injecting powder into the nest of at Hallahan’s Orinda yard. The treatment method relies on the worker yellowjackets to carry the powder deep into the nest, where it kills the queen — if all works as planned.
The yellowjackets swarmed over Budge’s suit, likely marking her with a chemical pheromone that designates her as a threat to attack.
“They are very aggressive in defending their nest,” Budge said. “The problem is when they nest near people’s homes, a person walking or or near the nest can be attacked.”
Underground yellowjacket nests can hold as many as 5,000 wasps.
Some people are allergic to the wasp stings. Unlike honey bees that sting once and die, yellowjackets can sting repeatedly.
Ecologists say yellowjackets serve an important ecological role by consuming many types of insects. But in the fall, yellowjackets are hunting for food sources to survive the winter.
“They are looking for meat and sugary substances,” said Andrew Pierce, a Contra Costa Vector District spokesman. “Unfortunately, that could be your barbecue chicken and your soda.”
Sometimes, homeowners, restaurants or businesses make the mistake of placing a yellowjacket trap in the immediate vicinity of where people will sit or dine outdoors, Pierce said. Traps should be placed far away from seats or dining areas to avoid luring in the wasps to likely contact with humans and their food and drink.
- Avoid yellowjacket nests if possible.
- To avoid getting stung, don’t go barefoot and don’t swat yellowjackets with your hand. Keep garbage cans away from eating areas.
- If ground nests are in an area that can’t be avoided, call a public vector control agency or private pest contractor.
- Yellowjacket traps are most effective if hung outdoors in February and March in time to catch queens before they can establish a colony.
- Many vector control districts have online forms allowing people to report yellowjacket problems.
- The Contra Costa Mosquito and Vector District can be reached at 925-771-6172.
- The Alameda County Vector Control District can be reached at 510-567-6800.
- The Santa Clara County Vector Control District can be reached at 408-918-4770. (Santa Clara’s agency offers advice, but does not treat yellowjacket nests on private property.)
- The San Mateo County Mosquito and Vector Control District can be reached at 650-344-8592.
Published at Thu, 07 Sep 2017 12:58:10 +0000