At the first scent of barbecued steaks on a recent Friday evening, the yellow jackets started coming. The predator wasps spread the word with the hive and a small swarm quickly arrived.

They dive-bombed “the beef and Cabernet Sauvignon,” said Matt Proietti, who relayed the incident, which millions of the wasps have replicated in some form this year across California. “We had to eat our rib eyes inside.”

An epidemic-level incursion of yellow jackets hit a peak last week. A man was killed after a reaction to yellow jacket stings at Huntington Lake in the south Sierra foothills, and across the state, yellow jacket traps are killing unbelievable numbers of the predator wasps.

With cooler weather not far off, yellow jackets are preparing for winter with feeding frenzies during the last warm afternoons of late summer and early fall. The hungry wasps — some call them “meat bees” — this year have affected picnics and campgrounds across much of the state.

At his home in the foothills of Nevada County, Proietti got redemption when he put up a yellow jacket trap that was baited with a sex pheromone liquid in a cotton ball. In six days, he caught an estimated 750 yellow jackets; the photo of his trap loaded with yellow jackets is like something few have seen. By using wasp pheromone liquid as bait, no bees or other unintended insects are caught.

In July, I wrote a story about how I was stung by swarms of yellow jackets on two occasions after accidentally stepping on nests in the ground. With three other small encounters in a month, I was stung about 30 to 40 times. Each jolt felt like getting shocked by electric cattle prods or burning needles. My love for all things in nature was thereby reduced by one species.

Turns out a lot of people feel the same way.

After that story, reports came in from across the Bay Area, Tahoe, the Sierra Nevada and elsewhere in California. The consensus with most scientists is that last winter’s rains after several drought years caused booms in many insect species, including yellow jackets. They often make nests in gopher holes, crevices in downed logs and hollow spaces in walls and trees.

At Tahoe, field scout Jim Budny reported the incursion started in midsummer. “Worst I’ve seen in 38 years up here,” he said. In South Lake Tahoe, health specialists echoed that opinion, saying they removed 345 wasp nests in August alone (compared with 232 in August 2012). “Way more of them than usual,” said Dan Miller. “They’ve become a big problem at beaches, campsites.”

On the North Yuba River last week, yellow jackets forced Chris Begley and his pals out of Wild Plum Campground, and they ended up in the Sierra at Plumas-Eureka State Park. “An infestation,” Begley reported.

At Tahoe and across the Sierra Nevada, the hope is that last week’s cold snap will knock the yellow jackets off their feet for a while, but typically, wasps stay active and hungry as long as the afternoons are warm through September and early October.

Outside of Fresno, pest control services called this the worst year for yellow jackets and other wasp species in 20 years.

For those who have severe reactions to the toxins from stings, the consequences can be devastating. Mike Bracci, the cousin of Chronicle field scout John Hibble, died this month after yellow jackets attacked him.

“Our cousin was closing up our cabin at Huntington Lake,” Hibble said. “He was gathering wood just uphill from our cabin when he was attacked. He collapsed and died. The fire department was not allowed to carry EpiPens and by the time the ambulance arrived he was dead.”

Repellents and remedies

In addition to treatment with epinephrine (EpiPen) for those allergic to the toxin injected in stings, Chronicle readers have sent in the following suggestions:

Repels everything: Wear a sheet of Bounce (fabric softener) to repel wasps, said Judy Parsons.

Scrape the stingers: If you get a stinger in your skin, “Don’t squeeze them out, but scrape them off (to the side, as with a credit card), or more poison will be injected,” wrote Jim Simon of the American College of Emergency Physicians.

Treatments: SssstingStop, advises Jocasta Mettling; sun cream, says Claire-Laure Belt; a mudpack or Ancient Healing Salve, wrote Willie Gilbert; witch hazel and later anti-itch cream, advises wife Denese Stienstra; Medicaine swabs, says Toby Freedman; vinegar for wasps, bicarbonate for bees, says Peter Williams.

Diablo bike statistics

In a follow-up on the recent story about the new road striping, signs and hopes of reducing the number of bike accidents on the road up to Mount Diablo, Al Kalin, president of the Mount Diablo Cyclists, provided the following numbers:

Vehicle numbers: In 2014, 120,000 to 150,000 cyclists rode up Mount Diablo, representing 40 to 50 percent of all vehicles making the trip.

Collisions: In a four-year span, there were 100 collision reports, roughly one every two weeks; 70 percent occurred on blind curves. Of solo bike collisions, 57 percent involved unsafe speed and 43 percent were mechanical failures.

What rangers dream of: Cars heading up Mount Diablo need to slow way down, and bikes need to stay in single file. Heading downhill, both need to slow down. When cars are backed up and unable to pass uphill, everybody needs to relax, take a deep breath and wait until bikes have a safe place to pull over to the right. The result? No more accidents and conflicts.

Crystal Springs

Last Monday’s resolution to allow for increased access for hiking and mountain biking on the roads at the Crystal Springs Watershed on the Peninsula was passed out of the Land Use Committee and will be addressed by the San Francisco Board of Supervisors. Amid the public support, several prominent local environmentalists opposed the resolution. I’ve been all through the 23,000-acre watershed, am the first to want to protect natural resources, and don’t see how letting people get a permit to walk or ride on roads would have an impact.

Cool sightings

Ring-tail: On remote Highway 162, the Oroville-Quincy Highway in the northern Sierra, R. Rickman reported a rare sighting last week of a ring-tailed cat (raccoon family), running across the road. “Beautiful.”

Shearwaters: A massive flock of shearwaters, the low-flying seabirds that can span for miles, arrived along Point Reyes National Seashore south of Limantour Beach last week, reported John Bielenberg. “After 15 years of going to Point Reyes, I had never seen that before.”

It can be an amazing sight. I once saw a flock south of Half Moon Bay that spanned 7 miles long from Lobitos Creek to San Gregorio.

Tom Stienstra is The Chronicle’s outdoors writer. He is the author of “Moon Northern California Hiking.” E-mail: tstienstra@sfchronicle.com Twitter: @StienstraTom