News Release
July 30, 2007

Landscaping Tips: Yellow jackets generally unwelcome garden guests

By Scott Hininger, extension educator, and Scott Schell, assistant extension entomologist, UW CES

Bees and wasps are generally considered beneficial insects in the garden because of their pollination and predatory activities. They can, however, become a pest or even life threatening if a person with allergies to the insects is stung.

Almost every August, Wyoming residents become concerned with yellow jackets, which are members of the paper wasp family (Vespidae). This August will be no exception as soaring temperatures and drought have concentrated wasp foraging activities to people’s green yards and gardens.

The nests of wasps found in Wyoming are started by one fertilized young queen that survived the winter. This nest is enlarged as the summer progresses, and the number of worker wasps increases. Depending on the species of ground nesting wasps, there can be as few as 75 workers to more than 85,000 in extreme cases.

Only the queens produced this summer will survive the winter to start things over next year.

The smooth bodies of yellow jackets are usually boldly marked with yellow or white against black; this coloration pattern is a warning to leave them alone.

There are two main types of paper wasps – the aerial nesting wasps that build gray, papery nests above the ground in tree branches or under the eaves of buildings, and wasps that nest in the ground or within structures, usually in old rodent burrows but occasionally in the hollow walls or attics of buildings.

The aerial nesting wasps generally take only live insect prey and don't usually bother humans unless their nests are disturbed; however, the two most common species of ground nesting wasps in Wyoming, the western and common yellow jackets, will readily scavenge food at picnics and become bothersome and potentially dangerous.

Yellow jackets feed primarily on protein, mainly in the form of other insects, but they also like sweet things such as soda pop, sugary foods and fruit. Some perfumes and aftershaves can also attract them. The wasps consume the sweets, but take the protein food – including meat ready for the barbecue – back to their nests for the young.

The end of the summer, when natural sources of food begin to diminish, is when yellow jackets readily invade garden parties, barbecues and other outdoor activities.

All meat, desserts and fruits should go directly from a covered container or cooler onto a hot grill or a diner’s plate. 

If a worker wasp finds a plate of raw hamburger or other meat in the open waiting to be cooked, she will bring lots of her sisters back for a share and spoil the fun. (Females can control whether they produce male or female offspring. Female workers are produced earlier in the season while males are produced at the end of the season to breed with the next generation of queens.) 

Open cans of pop are a real hazard as wasps can crawl into the cans, and then they can sting an unwary drinker in the mouth. Mugs with closeable openings are the safest. Glasses and cups with open tops can also be used.

All garbage, as it is created, should go directly into tightly lidded garbage cans away from where people are gathered. Wasps can chew through plastic garbage bags.

How can homeowners get rid of wasps?  Insecticide products developed and labeled specifically for wasps should be used, following the directions. Don’t try gasoline on wasp nests as it can create a fire hazard or contaminate ground water.

The paper wasps that build nests aboveground are generally easier to find and kill than the belowground nesters. If a nest is located, mark its location and come back and treat it at night. This will reduce the chance of being stung since workers forage during the day.

Wasp traps work, but people generally don't start using them until it is too late in the summer when the workers are already numerous. If traps are set early in the spring and kept in use through the summer, they will at times catch queens and the first few workers, which could destroy or severely set back a localized population.

Fogging or aerial spaying of broad-spectrum insecticides is not recommended because too many beneficial insects, including honeybees, can be killed, and the source of the wasps will not be eliminated.

Contact: Robert Waggener, Editor
Phone: (307) 766-3571
E-mail: robertw@uwyo.edu

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