The Time to Prevent Yellowjackets is Now


The weather warms; you fire up the grill, throw on the chicken, and plan to enjoy dinner on the patio. Within minutes, there’s one yellowjacket hovering around the grill, then, more and soon several yellowjackets force you to change plans and move your meal indoors. This scenario is no surprise, because 2017 turned out to be a record-setting year for yellowjackets in Contra Costa County.

The District received a record-breaking 1,352 requests for ground-nesting yellowjacket inspections — up 142 percent compared to the average number of requests the District received during each year of California’s recent five-year drought.

The 411 on Yellowjackets

    • Four common species of yellowjackets are in Contra Costa County.
    • Two species build nests in trees and areas above ground, two species build underground nests that are out of obvious view.
    • All eat smaller pest insects and provide incidental pollination to plants.
    • Risk to public health
    • All can sting and bite repeatedly to defend their nests.
    • All are dangerous for those who are allergic.
    • Underground nests make unexpected encounters more likely.
    • Underground species can be scavengers and may be inclined to go after our food.

The key to reduce the risk of yellowjackets this year is to be proactive now.

Why Yellowjackets Live Under Our Feet

Yellowjacket queens hibernate over winter. They emerge when the weather warms to look for a suitable nest location which can be:

  • An abandoned rodent burrow
  • Between railroad ties
  • Among the roots of some shrubs
  • Under log piles or any other subterranean void

Once she finds the location, the queen builds a nest out of chewed up wood scrapings or plant fibers. The nest is where the queen raises workers that will forage for food to feed the growing colony.

How to Reduce the Risk of Yellowjackets This Year

Yellowjacket traps are an effective way to reduce the population of yellowjackets on your property. With ground-nesting yellowjacket activity expected to begin now that the weather has been unseasonably warm, it is time to put up traps to catch the yellowjackets that emerge from their nests.

  • Find reusable yellowjacket traps at many home and garden stores.
  • Hang traps high in trees at the edge of your property and as far away from where people or pets live and play.
  • Using fruit juices in the traps at this time of year may attract queens.
  • Also, use the pheromone insert that is sold to attract the worker yellowjackets because it mimics their own hormones and attracts them to the traps.

What to do if You Find a Ground-nesting Yellowjacket Nest on Your Property

People often encounter ground-nesting yellowjacket nests by accident while working or playing in the yard. When someone walks or uses equipment on the ground, the vibration can be felt in the underground nest causing yellowjackets to emerge — biting and stinging repeatedly as their first line of defense. That is why the first thing to do if you see yellowjackets coming out of a hole in the ground or out from under a bush on your property is:

  • Place a flag, tool or any other handy item on the ground relatively near the nest to mark the nest for inspection and then get to a safe location.
  • Once you are safely away from the yellowjackets, draw a simple map to show the layout of your yard and where the nest is located.
  • Tape the map to your front door or gate.
  • Call the District or go online to request ground-nesting yellowjacket service.

What Happens During the District’s Ground-nesting Yellowjacket Inspection

A District employee typically responds to your request within 48 hours, Monday – Friday. The District employee will use the map and the item you have left near the nest to locate it and verify that they are yellowjackets. Then, the District employee will treat the nest with an insecticidal dust. Once treated, keep people, pets and water away from the nest for 8 hours as yellowjacket activity can continue while foraging workers return to the nest posing the risk that they may sting or bite.

For more information on the District’s free service to treat ground-nesting yellowjacket nests, visit the District’s website.

And remember, to reduce the risk of yellowjackets before they become unwelcome guests at your outdoor barbecue this summer, act now. Hang up traps, follow the instructions, and use a fresh attractant insert to stay one step ahead of the colony before the yellowjackets set another record this year.

About Kevin

Councilmember - City of Oakley, Manager of Mainframe Operations and Optimization – USS-POSCO INDUSTRIES, Co-Founder and Board Member - Friends of Oakley A Community Foundation, Commissioner - Contra Costa Transportation Authority, Board Member - Tri Delta Transit, Transplan, San Joaquin Joint Powers Authority and RD 2137, Advisory Board – Opportunity Junction
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