The buzz on wasps: high populations linked to mild winter |

The buzz on wasps: high populations linked to mild winter

Claire Cudahy
The western yellowjacket population in the region is booming due to a mild winter and spring.
Kathy Garvey / UC Davis |


There are two distinct types of social wasps in Western states—yellowjackets and paper wasps. Yellowjackets are the most common in this region.

Yellowjacket colonies live only one season, but in coastal California south of San Francisco, they can survive for several years and become quite large.

The yellowjacket is sometimes called the “meat bee.”

Yellowjackets build their nests of paper from wood fibers and saliva.

Source: UC Davis, Department of Entomology

Patio dining may not be quite as desirable as of late thanks to some uninvited pesky guests.

Diners in the Lake Tahoe Basin have noted a marked increase in the number of wasps buzzing about — and they aren’t afraid to help themselves to whatever food is on your plate.

Lynn Kimsey, a professor of entomology at UC Davis and director of the Bohart Museum, said the culprits are western yellowjackets, and the surge in its population is due to a mild winter and spring.

“Without extreme temperatures and not as much snow, there is more queen survival,” explained Kimsey.

According to Kimsey, this time of year male workers and new queens are produced. They mate, and around October the queens find holes to nest in. At first frost, all the workers — the wasps that we see buzzing about — die, but some of the queens survive and emerge to form new colonies in the spring.

“You have a lot of colonies founded in the spring and there is a lot of food available from garbage and road kill,” said Kimsey. “These guys are scavengers. Most yellowjackets go after live insects, but they will eat your hamburger or whatever else, too. This time of year they are winding down and will be attracted to sweets and sugars.”

Kimsey said that the population will eventually “crash,” but at this point in the season there isn’t much to be done.

“What you really need to do is put out those florescent green traps in the late spring and early summer because right now the population is just too huge.”

Individual colonies can reach populations of between 1,500 and 15,000.

Kimsey noted that the yellowjacket is “not terribly aggressive,” but can be if you get too close to its colony, which can be tricky to spot since they are mostly underground or hidden in hollow trees.

The wasps tend to be medium sized and black with jagged bands of bright yellow on their abdomens. Because wasp stingers have no barbs, it can be used repeatedly, especially if one happens to get inside your clothing.

The last boom in the yellowjacket population in the region took place in 2013.

Lucky for us, however, even a mild winter is enough to keep the population in check unlike in a place like Hawaii.

“This species has gotten introduced into Hawaii and because it’s never cold the colonies become perennial, not annual, and they never die,” explained Kimsey. “They found a colony that was 6 feet long by 3 feet and had more than 5 millions workers.”

Kimsey recommends that Lake Tahoe residents put out traps next spring to keep the yellowjacket populations at normal levels.

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