A Western yellowjacket, Vespula pensylvanica, sipping water at UC Davis. (Photo by Kathy Keatley Garvey)

Yellowjackets, commonly known as "meat bees," in comparison to the "vegetarian" honey bees, will be among the wasps featured at the Bohart Museum of Entomology's open house from 1 to 4 p.m., Sunday, Sept. 25 in Room 1124 of the Academic Surge Building, 455 Crocker Lane, UC Davis campus. The theme: "Weird and Wonderful Wasps."

The open house is free and family friendly. A family arts and crafts activity is also planned.

"Yellowjackets are social wasps that build large, hidden nests," writes Lynn Kimsey, director of the Bohart Museum and a UC Davis distinguished professor of entomology, on one of her online fact sheets. "The nests are usually subterranean in rodent burrows or in cavities in trees, walls or attics. 

"Yellow jacket nests can be huge with 50,000 to 100,000 workers," Kimsey points out. "In temperate climates these colonies are annual. Their nests die in the fall after producing new queens. New queens produced by the colonies in the fall spend the winter in protected places until spring when they found new colonies. Yellow jacket colonies can become perennial in warmer climates, such as in Hawaii and coastal California. In these situations the nests can become enormous, with millions of workers!"

Kimsey says that yellowjacket nests "can be distinguished from paper wasp nests because the brood cells are encased in a paper envelope so they can't be seen without taking off the outer envelope. These wasps generally feed on live prey, but the pest species, such as Vespula pensylvanica, will scavenge other sources of meat and sugar, including sodas, hamburgers and road kill. They will also visit aphids and scale insects for honeydew."

At the open house, visitors will learn about the smallest fairy wasps  to the "murder hornets"; what role wasps play in plant galls and figs; and how to distinguish a parasitoid from a parasite.  Kimsey will discuss the Asian giant hornet, Vespa mandarinia. A single colony of the Asian giant hornet was found and destroyed Sept. 18, 2019 in Nanaimo, Vancouver Island, Canada, and a single dead hornet was found Dec. 8, 2019 in nearby Blaine, Wash. Since then, it also has been sighted-- and destroyed--in both Canada and Washington state.

Fairy wasps, in the family of chalcidoid wasps, are tiny insects. They include the world's smallest known insect, with a body length of only 0.139 mm (0.0055 in), and the smallest known flying insect, only 0.15 mm (0.0059 in) long, according to Wikipedia. The fairy wasps are found in temperate and tropical regions throughout the world. The family contains approximately 100 genera with 1400 species. All known fairy wasps are parasitoids of the eggs of other insects, Wikipedia says, "and several species have been successfully used as biological pest control agents."

(See Bug Squad blog on European paper wasps and Bohart Museum Fact Sheet comparing yellowjackets to European paper wasps.)

Dec. 22 marked the winter solstice, the first day of winter.

But don't tell that to the western yellowjacket, Vespula pensylvanica.

It's supposed to be hibernating, not flying.

But there it is flying around--and sipping nectar--from flowering Algerian ivy climbing a fence in Vacaville, Calif.

It has company. Nearby, several other yellowjackets, honey bees and hover flies are participating in the nectar feast.

Not much is blooming this time of year!

So, what is winter solstice? According to the Farmer's Almanac, "Winter solstice is the day with the fewest hours of sunlight during the whole year. In the Northern Hemisphere, it always occurs around December 21 or 22. (In the Southern Hemisphere, it is around June 20 or 21.)"

Now the days are getting longer.

Is it spring yet?

A yellowjacket and honey bee sharing the same flower. (Photo by Kathy Keatley Garvey)

A recent visitor at a camp in the Sierra Nevada mountain range witnessed a large number of wasps and stinging behavior. They crowded around the picnic tables (ah, meat!) and sipped from soda cans (ah, sugar!) She wondered if they were yellowjackets or European paper wasps.

From the description and behavior: yellowjackets.

"European paper wasps (Polistes dominula) are not scavengers," says Lynn Kimsey, director of the Bohart Museum of Entomology and a professor of entomology at UC Davis. "They only take live insects, particularly caterpillars. Western yellowjackets, Vespula pensylvanica, are serious scavengers and are major pests in the Sierra and elsewhere. Their colonies are annual, which means that fertilized new queens must overwinter in protected places until it warms enough in the spring to begin new colonies. As the new colonies are building they need a lot of protein for their babies. The larger the colonies get the more they need."

"If many new queens survived the winter because temperatures were warmer and drier than usual then there will be many colonies to deal with, all competing for food. By late in the season the colonies go more into maintenance mode, needing a lot of sugar. They aren't feeding many babies, which need protein, and the large number of adults need sugar for fuel."

"At this point, control is largely useless," Kimsey says. "Control measures need to be started in the mid to late spring and the best control method is the use of baited traps, not spraying. Also when colonies are found they need to be removed--this needs to be done at night. These wasps nest in cavities, mostly in the ground but also in attics, wall voids and hollow trees if available. The large number of stings suggests that a colony or colonies were nearby."

"So at this point it's best to hope for a long cold, wet winter," Kimsey says.

The UC Statewide Integrated Pest Management Program (UC IPM) provides a wealth of information on Western yellowjackets and paper wasps on its PestNote: "In Western states there are two distinct types of social wasps—yellowjackets and paper wasps. Yellowjackets are by far the most troublesome group, especially ground- and cavity-nesting ones such as the western yellowjacket, which tend to defend their nests vigorously when disturbed. Defensive behavior increases as the season progresses and colony populations become larger while food becomes scarcer. In fall, foraging yellowjackets are primarily scavengers, and they start to show up at picnics and barbecues, around garbage cans, at dishes of dog or cat food placed outside, and where ripe or overripe fruit are accessible. At certain times and places, the number of scavenger wasps can be quite large."

"Paper wasps are much less defensive and rarely sting humans," according the to the UC IPM PestNote. "They tend to shy away from human activity except when their nests are located near doors, windows, or other high-traffic areas."

The UC IPM authors point out that "Typically, previously mated, overwintering yellowjacket and paper wasp queens begin their nests in spring when the weather becomes warm. The queen emerges in late winter to early spring to feed and start a new nest. From spring to midsummer, nests are in the growth phase, and larvae require large amounts of protein. Workers forage mainly for protein at this time—usually other insects—and for some sugars. By late summer, however, the colonies grow more slowly or cease growth and require large amounts of sugar to maintain the queen and workers; foraging wasps are particularly interested in sweet things at this time. Normally, yellowjacket and paper wasp colonies live only one season. In very mild winters or in coastal California south of San Francisco, however, some yellowjacket colonies survive for several years and become quite large."

UC IPM has posted an informative YouTube video, "Distinguishing Between Yellowjackets, Wasps, and Look Alikes." Look closely and you can see that those European paper wasps have distinctive orange antennae. Yellowjacket antennae are black. 

Or, to put it another way: Yellowjacket antennae are black, like the Oakland Raiders' logo, and European paper wasp  antennae are orange, like the logo of the San Francisco Giants.

Bee specialists like to point out that the yellowjacket is a carnivore and the honey bee is a vegetarian.

They are, indeed. The yellowjacket is an aggressive predator that seeks protein-rich foods for its colony, while the honey bee--usually quite passive unless it's defending its hive--gathers nectar and pollen.

If you've ever watched a yellowjacket invade a honey bee hive or prey upon other insects--or grab a bite of chicken from your barbecue or scavenge rotting fruit--you know how aggressive it is. 

We watched a western yellowjacket, Vespula penyslvanica (as identified by Lynn Kimsey, director of the Bohart Museum of Entomology and professor of entomology at UC Davis), forage on a cluster of red-hot pokers along a road leading to Tomales, a tiny town in Marin County.

This wasn't a "red" red-hot poker, though. It was yellow. Varieties of the Kniphofia genus (the genus was named for 18th century German physician/botanist Johann Hieronymus Kniphof) now appear in such colors as orange, coral, cream and yellow.  

Rather fitting that a yellowjacket was on a yellow red-hot poker!

We caught it in flight as it headed toward the tubular flowers and watched it grab a few tasty morsels, an unsuspecting spider or two, to carry back to the nest. (It also sips nectar for flight fuel.) When it emerged, it was dotted with pollen grains, so you could say that sometimes it's a pollinator, too. But not a significant one...

The western yellowjacket,  native to the western United States, is a major pest in Hawaii, where it was first discovered in 1977. Erin Wilson, a former postdoctoral scholar in the Louie Yang lab in the UC Davis Department of Entomology, studies this social, ground-nesting wasp. 

Wilson, who launched the vespularesearch.com website, describes it as a "vacuum cleaner" that wreaks ecological havoc among the native species in Hawaii. 

“The introduction of non-native organisms is a leading cause of imperilment of native species,” says Wilson, who has studied the western yellowjackets at two sites: the Hawaii Volcanoes National Park on the island of Hawaii and the Haleakala National Park on Maui since 2004. 

Scientists have found that the incidence of perennial or overwintering colonies is higher in Hawaii than in its native range.

Compared to annual colonies, these overwintering perennial colonies can collect twice as many prey items and produce 10 times the worker force, Wilson says. Some perennial colonies are huge, their size linked to Hawaii’s mild climate and the ability of the yellowjackets to establish perennial colonies. How huge? One Maui colony yielded 600,000 individuals. Compare that to a typical California colony of less than a few thousand wasps.

Read the PBS piece about this invasive insect in Hawaii and see it "stinging" the camera lens.