What’s Up with the Yellowjackets?

 

During the fourth week of October my school tour group noticed a very active yellowjacket nest at the bottom of the stairs on the Bluff Trail. Dozens of yellowjackets could be seen flying rapidly in and out of an old gopher hole. For some it seemed a pretty scary sight. A few days later the yellowjackets were gone. What happened?

Entrance to the abandoned yellowjacket nest a formerngopher hole.

We could see that the nest entry hole had been enlarged and there were pieces of paper “honeycomb” tossed around. A close look at the combs revealed a few live yellowjacket larvae and pupae still inside some cells but the nest was destroyed and no adult wasps were in sight.

Three white yellowjacket larvae are visible in the cells of this yellow jacket nest comb.

The culprit was probably a skunk. (In fact there was a strong skunk scent along the trail that day). But a raccoon could also have carried out the job. These digging animals love to feast on insect larvae and a yellowjacket nest will contain hundreds if not thousands of them. The thick fur on these animals protects them from most yellow jacket stings.

Striped skunks may dig up yellowjacket nests and eatnthe larvae and pupae. (Photo by Jerry P Clark UC IPM)

Do yellowjackets keep you off the trails? Rest easy as they will soon be gone.  Although yellowjackets are quite abundant and aggressive in October and early November they will be mostly a memory by December when temperatures drop. 

In fall yellowjacket colonies start producing reproductive males (drones) and females (queens). Only the new reproductive queens will survive the winter. The workers drones and any larvae or pupae in the nest will die with the onset of cold weather. After mating the new queens find hiding places in attics sheds log piles or other sheltered places and remain inactive and rely on body fat for energy until warm weather returns.

In early spring the overwintered queens seek out nesting sites. A vacant ground squirrel or other rodent hole is ideal. Once a site has been selected the queen will begin to build a honeycomb-like nest of paper she makes by chewing wood fibers mixed with saliva. She will lay eggs in the cells of the comb and provision each cell with food usually insects for the hatching larvae to eat. The legless white larvae remain and grow within the cell completely dependent on their mother’s care.   After a few weeks the larvae pupate in the cells and emerge as adult workers which are sterile females.

After the first group of a dozen or more workers emerge they take over the foraging and nest building work and the queen remains underground in the nest devoting her full time to reproduction. 

Over time the nest can get very large with multiple layers of combs (see drawing below) and several thousand workers. During the rapid growth phase in spring and summer workers are foraging mainly for protein such as insects or meat to feed the larvae. By late summer the colonies grow more slowly and they refocus on gathering sweet things to feed the new queens and workers. Food becomes harder to find in late summer and fall and this is the time when yellowjackets get most aggressive and also when you are most likely to encounter them along the trail.

Yellow jacket nests are built gradually over the season often in a gopher or other rodent hole in the ground.  In early spring the queen makes one paper comb to produce the first workers.  Additional layers are then built by the workers through the summer. Illustration by A. L. Antonelli from UC ANR Publication 7450: Pest Notes: Yellowjackets and Other Social Wasps.

 

Only female yellowjackets sting. The stinger is actually a modification of the egg-laying organ. Unlike honeybees yellowjackets are able to sting multiple times because their stingers don’t get embedded into the skin. Yellowjackets sting to protect their nests or themselves. They are the most aggressive of the wasps and are responsible for the vast majority (90% or more) of bee and wasp stings in the western U.S.

Although nobody likes being stung by a yellowjacket these wasps play an important role in our ecosystems preying on many insects scavenging dead animals and scat and providing food for skunks raccoons and birds. For information and videos on managing them in parks and backyards see the University of California Pest Note: Yellow Jackets and Other Social Wasps at https://ipm.ucanr.edu/PMG/PESTNOTES/pn7450.html.

 

Text by MarynLouise Flint  Docent Effie Yeaw NaturenCenter and Extension Entomologist Emerita UC Davis

Photos bynJack K. Clark and Jerry P. Clark used with permission from the University ofnCalifornia IPM Program.   Other photos bynMary Louise Flint.