Western yellowjackets are a ground or cavity nesting species common in Colorado. A medium sized wasp, western yellowjackets are black with uneven bright yellow bands. They have a narrowed, waist-like appearance where the thorax and abdomen meet. Mated queens overwinter reemerging in the late winter to early spring to begin feeding and building a new nest for her seasonal colony. As workers hatch, they will take over the responsibility of nest expansion, collection of food and caring for the young. Most western yellowjacket nests are in abandoned rodent burrows or other cavities in which a single entry is most common. In the event that the cavity is too small, workers will moisten the soil and dig in order to expand the space. Nesting can also occur in wall voids or other cavities in homes and structures. Expansion in those cases can result in damage to drywall which may expose the nest to the interior of the structure. Unlike paper wasps, yellowjacket nests are enclosed in a paper-like envelop with a single entrance most commonly located at the bottom of the nest. By the end of the season, colonies may contain 1,500 to 15,000 yellowjackets depending on their specific species. Nests are made of saliva which is mixed with wood fibers resulting in a paper-like substance. Yellowjackets may also create aerial nests which are located at least 3 feet off the ground and have the same paper covered appearance.
Western yellowjackets will defend their nest vigorously when disturbed or when feeding and lack barbs on their stingers which allow a single yellowjacket to sting multiple times. Although they are considered beneficial predators of nuisance pests such as flies and many plant feeding insects, they are also the species that is of most concern for stings due to their aggressive nature and multiple sting capability. As with other stinging insects, yellowjacket stings can result in a wide range of reactions from the recipient. Mild reactions may include localized pain and swelling whereas adverse reactions can lead to anaphylactic complications and even death. If stung, it is important to remember to immediately leave the area to avoid being stung again. Stings also commonly occur when yellowjackets crawl into beverages unnoticed during outdoor events as they come in contact with lips, mouth or throat of the person consuming the drink.
Commonly referred to as “meat eaters”, western yellowjackets seek out protein based products for a majority of the first half of the season. Meats at picnics, barbecues, and trash receptacles as well as proteins based pet foods such as dog and cat foods may attract high quantities of yellowjacket populations. This is especially common from spring to midsummer, a time in which peak growth of the colony occurs. The latter portion of summer and into the fall, workers tend to shirt to high carbohydrate products such as juices, nectar, soda and other sweets to provide hydration and energy to the colony. A majority of colonies will not overwinter and will die off in the fall. In milder climates, some colonies may be able to sustain themselves through the winter.
Although there are natural predators of western yellowjackets, including birds, reptiles, amphibians, skunks, baldfaced hornets and raccoons, natural predators rarely provide adequate control of yellowjacket colonies. Areas of known activity should be avoided by both humans and pets whenever possible. Yellowjackets typically forage within ¼ mile of their nesting site. Treatment of active western yellowjacket nests is best completed by a well equipped professional. Over-the-counter yellowjacket traps are available with pheromone and protein lures. To reduce activity near a specific area, traps should optimally be placed 150 feet apart and roughly 200 feet from the area in which you want to decrease yellowjacket activity.