Paper Wasps and Yellowjackets - August 25, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Paper wasps and yellowjackets are beneficial insects. They feed on caterpillars and other insects that could damage crops and ornamental plants in your garden. They also feed on house fly and blow fly larva. Paper wasps and yellowjackets are social insects that become aggressive when their nests are approached or disturbed. This is often when people and animals are often stung. These stings are painful and can be life threatening to allergic individuals. Even so, these insects should be respected and tolerated under most conditions.
Paper wasps have long hind legs and a distinct constriction of the body between the thorax and abdomen. They are common in urban and suburban areas where they can build their nests under eaves of structures or in other protected locations. The benefits of wasps usually outweigh potential for harm unless a nest is in a high traffic area such as a doorway or outdoor living area. When approached, paper wasps leave the nest and dive bomb intruders occasionally inflicting painful stings. Both paper wasps and yellowjackets can sting multiple times.
Yellowjackets forage for a broad range of foods, but they often come into conflict with humans when they are attracted to meat, carbonated beverages, juices, desserts, and other food items. They are commonly a nuisance to outdoor diners during the summer months. Yellowjackets will often enter cans of sweetened carbonated drinks. Unknowing drinkers can find an agitated yellowjacket in their mouth. This can become serious if an allergic individual is stung in the mouth or throat. Yellowjackets also gather around uncovered trash receptacles where they freely gather food.
The western yellowjacket usually nests in the ground using an abandoned burrow, but can occasionally nest in crawlspaces or wall voids. Underground nests can be disturbed unknowingly by hikers and outdoor workers. When this happens, the yellowjackets emerge from the nest and attack the intruder. Underground, the nest is a papery structure that provides a home and breeding area for the queen and contains cells where young are raised.
Paper wasps and yellowjackets use a nest for one year although paper wasps may construct a new nest adjacent to an old one. This is important when considering the need for control. Keeping in mind that these insects are beneficial, where the nest is not posing an immediate threat to people or pets, it can be left for the season and removed during the winter months.
Some gardeners intentionally attract paper wasps to their gardens by building nest boxes which consist of a wooden box at least 4” x 4” x 4” which open on the bottom. The box is attached to a sturdy post mounted several feet above the ground. Of course, these nest boxes should be in locations where people will not regularly disturb them.
Sometimes, paper wasps are too close to high traffic areas and must be removed. Exposed nests can be sprayed with aerosol products labeled for this use. They are usually synthetic pyrethroids which have a quick knockdown effect. These spray insecticides are marketed especially for wasps and yellowjackets and produce a spray stream of up to 20 feet. The nest should be sprayed at night after the wasps have returned from foraging. Do not use a flashlight as they will follow the light beam to its source. Remove and destroy the nest after adult wasps are dead and wash down the nest area with a jet of water to eliminate colony odors. This inhibits surviving wasps from reestablishing a nest in that location.
A similar approach can be used on ground nesting yellowjackets. Spray the entrance in the early morning or evening and leave it alone for a few days. There are some aerosol products that produce foam on contact and work well on yellowjacket nests. Traps can also be used when large numbers of yellowjackets are pestering outdoor diners. These traps are available in both reusable and disposable designs.
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Last Updated: August 19, 2010
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