July 15, 2017
Dot Zanotti Ingels
Summer is heating up and so is the troublesome yellowjacket feeding season. Last summer was an especially intense yellowjacket year in California. Trying to find any redeeming value to these generally unwelcome visitors is not easy, but here is what I learned that may help us live with them.
Yellowjackets are often thought to be bees, but they are actually a species of social wasp. Included in this group is the Western yellowjacket, Vespula pensylvanica, the most frequently encountered backyard species in Marin and sometimes called the “meat bee.”
Yellowjackets are social hunters that live in colonies containing queens, workers and males (drones). The colonies are annual. Only inseminated queens overwinter in protected places such as under bark, in leaf litter, in soil cavities or in man-made structure. The queen emerges when the weather warms up in late spring or early summer and selects a nesting site to build a small paper nest to lay her eggs.
Yellowjackets build primarily subterranean nests in rodent burrows or other soil cavities, but sometimes, they will select other protected cavities in walls and ceilings of houses to set up home. Nests are built of wood fibers scraped from wood mixed with saliva. They consist of multiple stacked combs that are completely enclosed by a paper envelope except for a small access portal. If they need more space, they increase the size of the nest by moistening the soil or surrounding fibers and digging.
After the eggs hatch from the 30 to 50 brood cells, the queen feeds her young for about 18 to 20 days. The larvae then pupate and emerge as small, infertile females called workers. The first adult workers take over caring for the larvae and queen, nest expansion and foraging for food. The queen stays home laying eggs and by midsummer the colony population can reach several thousand inhabitants. As the season wanes, males begin to appear and will mate with the females that will become queens. The new queens will build fat reserves to allow for hibernation.
After mating the males quickly die. The colony worker numbers dwindle as the adults leave the nest to die.
Adult yellowjackets feed on insects such as caterpillars and grubs and nectar and sweets such as fruit or tree sap. As the nest reaches its peak numbers they become increasingly assertive in their search for food.
Most social wasps are actually beneficial by eliminating large numbers of other pest insects. Unfortunately, they do not always nest in areas where there is little human or animal activity. They chose to nest near you. Most of the time yellowjackets are not aggressive. They do not, however, like their nests disturbed or have us swatting at them.
What can you do?
• Avoid the wasps. Stay away from nests. Discourage food sources by keeping garbage covered and your drinks and pet foods indoors or covered. Pick up dropped fruit. Unfortunately for us, once a wasp discovers a food source, it will continue to hunt in that area long after the source has been removed.
• Trap the wasps. The lure traps we can purchase can help reduce the number of wasps that are foraging in an area, but they do not eliminate large populations. For your backyard, place multiple traps about every 150 feet along the property line as far away from the patio area you are trying to protect. It is important to place the traps between your property and the native areas that are being used as the nesting sites.
• Discouraging or eliminating nests. There are nest sprays available to eliminate visible nests, but they must be used with extreme caution. Yellowjackets can become extremely aggressive if they sense a poison being applied to their nest. Hiring a licensed pest control company or contacting your local mosquito and vector control district could also be an option to protect you and your family.
For more information check out yellowjackets pest notes on ipm.ucanr.edu.