When a Davis resident felled a plum tree, hordes of green-eyed, apricot-colored insects tumbled from the wood.
What were they?
They buzzed like bees. They loomed larger than bumble bees. And they disliked being disturbed.
The Davis resident took them to the Bohart Museum of Entomology, University of California, Davis, for identification.
“Male carpenter bees, Xylocopa varipuncta, also known as Valley carpenter bees,” said entomologist Lynn Kimsey, director of the Bohart Museum of Entomology and professor and chair of the UC Davis Department of Entomology.
“Some of us refer to these males as ‘teddy bear' bees, because of their yellowish-brownish color and fuzzy burly bodies,” said UC Davis emeritus entomology professor Robbin Thorp, who studies pollinators. “The females are all black with violaceous (violet) reflections on their dark wings.”
All females in the plum tree holes escaped.
Carpenter bees, so named for their ability to tunnel through wood to make their nests, carve with their mandibles (jaws) but do not ingest the wood. Only the females excavate the tunnels, which average six to 10 inches in depth.
Carpenter bees, measuring about an inch long, are the largest bees in California. Their eggs are the largest of all insect eggs. The Valley carpenter bee egg can be 15mm long.
The males are territorial, Kimsey said, and can be quite aggressive. They hover and lie in wait for passing females.
“We have them around our home (in Davis) when the wisteria blooms,” she said. “Many people think they're bumble bees because of their size. They think they're fluffy yellow bumble bees.”
Thorp said he tries to convince people to learn to live with these bees as “they are important pollinators in our environment and have potential as pollinators of some crops.”
“Carpenter bees are beneficial in that they pollinate flowers in native 
“These bees are not currently managed for crop pollination,” Thorp said, “but there have been some recent studies of their potential for pollination of greenhouse tomatoes. They are good at buzz pollination and can be managed by providing suitable nest materials.”
Due to their large size, carpenter bees cannot enter tubelike blossoms such as sage, so they slit the base of corolla, a practice known as “stealing the nectar” (without pollinating the flower).
The Valley carpenter bee species is commonly found in southern California but is not all that well known in the Central Valley. “I have observed them in the field in southern California and in the Sacramento area,” Thorp said. “In the past few years, they seem to have become more common in the Davis area. I even found a dead male on my driveway (in Davis) a month or so ago.”
Carpenter bees, especially the most common species in the Central Valley, X. tabaniformis orpifex, are often mistaken for bumble bees. Like bumble bees, female carpenter bees exhibit similar size and coloration. However, a carpenter bee generally has a hairless, shiny abdomen while the bumble bee abdomen is typically covered with dense hair, and often with yellow markings.
Thorp said three species occur in California. “Of the three species, X. varipuncta (with the golden teddy bear males) and X. tabaniformis orpifex are the only two that occur in the Central Valley,” he said. “The third species, X. californica occurs primarily in the foothill areas surrounding the Central Valley.”
To build their nests, the females select telephone poles, fences, decks, railings, eaves, siding, outdoor furniture and tree trunks. They prefer bare, unpainted or weathered wood, especially redwood, cedar, cypress and pine. They generally avoid painted or pressure-treated wood.
Carpenter bees overwinter as adults in the tunnels and emerge in the spring.
Brian Turner, the Bohart Museum 's public outreach coordinator, said the sculpted holes in the chunk of plum wood that the Davis resident brought in “look professionally drilled.” The holes are elongated and intricately sculpted to contain the brood and food storage.
Turner released the male carpenter bees, but museum visitors can see the plum wood holes.
The museum, located in 1124 Academic Surge, is dedicated to teaching, research and service. It houses the seventh largest insect collection in North America. The global collection totals more than seven million specimens, and focuses on terrestrial and fresh water invertebrates.
The museum is also home of the California Insect Survey, a storehouse of the insect biodiversity of California's deserts, ountains, coast and great central valley.
