Yellowjackets receive their common name from their typical black and yellow color pattern. They are worldwide in distribution with about 18 species occurring in North America and 16 occurring in the United States. One or more species are found throughout North America, with major desert areas and the uppermost latitudes (summers of 3-50 degrees Fahrenheit) being the only exceptions.
PHYSICAL CHARACTERISTICS
Adult workers are about 3/8-5/8″ (10-16 mm) long depending on the species, with their respective queens about 25% longer. Their abdomen is usually banded with yellow and black, but several species have white and black bands. In addition, two northern species are also marked with red. When at rest, their wings fold from front to back. The worker’s abdominal color pattern is usually distinctive for each species but it can vary. Because of this, multiple specimens may be required for identification.
BIOLOGY
Yellowjackets are social insects and live in nests or colonies. The adults are represented by workers that are sterile females, queens, and males which come from unfertilized eggs and usually appear in late summer.
Typically, only inseminated queens over winter and do so in sheltered places. In the spring, she uses chewed-up cellulose material to construct a golf ball-sized paper carton nest of a few cells which will eventually consist of 30 to 55 cells covered by a paper envelope. One egg is laid in each cell and the queen feeds the developing larvae arthropod protein material and nectar. After about 30 days, the first 5 to 7 workers emerge and shortly thereafter take over all the work except egg laying.
The nest will eventually consist of a number of rounded paper combs which are open ventrally and attached one below another, and are usually covered with a many-layered paper envelope. Nest size vary greatly, between 300 to 120,000 cells, with average nests consisting of 2,000 to 6,000 cells. A nests will contain 1,000 to 4,000 workers at its peak.
Later in the season, larger reproductive cells are built in which queens will be reared. Males will also be reared, but they will do so in old worker cells. When the new queens and males emerge, they leave the nest and mate. Only the inseminated females hibernate and survive the winter. The founding queen, the workers, and the males all die.
In the south and southwest, however, some species (V. germanica, V. squamosa, and V. vulgaris) are known to maintain large perennial colonies. Such colonies often have multiple queens, tens of thousands of workers, and contain several million cells.
HABITS
Depending on the species, the overwintered queen will usually select either a subterranean or aerial nesting site. Most of the pest species are ground nesting with soccer ball to basket ball-sized paper nests. The German yellowjacket usually nests in large (6- 12 cu ft/0.17-0.34 cu m) structural voids in buildings in the United States and the western yellowjacket occasionally nests in buildings. The aerial yellowjacket commonly attaches its nest to shrubs, bushes, houses, garages, sheds, etc.
Those nesting in the ground typically select areas bare of vegetation or else clear an area around the entrance. Nest entrance guards exist to protect the colony, but yellowjackets are slow to sting unless the nest entrance is approached.
Typically, yellowjacket nesting is only a problem when a nest entrance is located near human activity. That being said, overwintering queens may enter the living space during the winter seeking warmth, but it can also happen in the spring when they are looking for a nest site.
HEALTH
Yellowjackets can inflict numerous painful stings. These stings often result in painful swelling and itching. At least 15-20 people are reported to die each year in the United States as a result of anaphylactic shock following yellowjacket stings.
CONTROL
Yellowjackets are considered beneficial insects because their food consists mostly of arthropods that are considered pests. Because of yellowjacket’s aggressive behavior, however, nests located close to occupied buildings, recreational areas, or within structures, will usually warrant control.
While it’s easiest to locate nest entrances during the day, control should be done at night when most of the yellowjackets are in the nest. It is highly likely for yellowjacket nests to have multiple entrances. If possible, it is best to make the application using a beepole or an extension-handle duster. Bee suits should be worn when treating yellowjacket nests.
If the nest is in the ground, dust an area for 6″ (15 cm) around the entrance hole and/or puff dust into the entrance holes. Apply an appropriately labeled pesticide dust.
If the nest is located in a wall void, then either dust the void via the entrance hole or apply an appropriately labeled aerosol pyrethroid and close the entrance hole. After a day, the wall void nest area should be opened up and cleaned out to prevent dermestid beetle, spider beetle, and/or psocid problems from occuring. If it’s not possible to open the wall void, treat the void with a long-lasting, highly repellent material and/or boric acid dust. Although the latter method may help matters, it may not prevent future pest problems associated with the dead yellowjackets in the wall.
Yellowjacket nests in buildings occupied by chemically sensitive people can be treated by fastening a PVC or cardboard extension tube to the exterior sheathing around the entrance hole. Before attachment, the interior surface exclusively should be treated with a nonrepellent pesticide formulation (dust, WP, ME, or SC). Additional interior coatings of the tube with pesticide may be necessary. This treatment should be done at night and while wearing proper protective equipment.
If it is an aerial nest, then an appropriately labeled aerosol works well. If possible, it is much safer to make the application from the ground using a beepole. If the application must be made during the daytime when many of the foragers will not be present, then dust is the choice because foragers will contact it upon their return.
In situations where pesticide application is not desirable, the use of baited traps can help reduce the number of adults. For German and eastern yellowjackets, grenadine has been found to be a very attractive bait. The traps should be placed 3-8 ft (1.8-2.4 m) above the ground, between the area to be protected and the nesting area, such that they are protected from passers by and the wind, and placed about 5 ft (1.5 m) apart at the height of the season. They should be checked daily, and cleaned and rebaited as required.