INTRODUCTION
Yellowjackets receive their common name from their typical black and yellow color pattern. They are worldwide in distribution with about 16 species occurring in the United States.

RECOGNITION
Adult workers about 3/8-5/8” (10-16mm) long depending on the species, with their respective queens about 25% longer. Abdomen usually banded with yellow and black, several species with white and black, and 2 northern species also marked with red. Wings folded longitudinally at rest. In addition, pronotum in lateral view almost triangular, extending to tegula (structure at base of front wing) or nearly so; front wing 1st discoidal cell about half wing length; hind wing lacks jugal lobe (lobe on rear margin near body); clypeus (front lip) broadly truncate and slightly notched; middle tibiae with 2 apical spurs. The worker abdominal color pattern is usually distinctive for each species but because it does vary, a series of specimens may be required for identification.

SIMILAR GROUPS
1. Baldfaced hornets (D. maculate) mostly black with yellowish-white markings on face, thorax, and end of abdomen.
2. European hornets (Vespa crabro) very large (up to 1 3/8”/35m long), brownish with orange stripes.
3. Honey bees (Apidae) with hairy eyes, hind tarsal 1st segment enlarged and flattened, hind wing with jugal lobe (lobe on rear margin near body), abdomen not banded with yellow and black,
4. Some clear-wing moths (Lepidoptera: Sesiidae) which resemble yellowjackets, with siphoning mouthparts.

REPRESENTATIVE SPECIES
1. The common yellowjacket, Vespula vulgaris (Linnaeus), is found throughout most of the United States.
2. The eastern yellowjacket, V. maculifrons (Buysson), is common east of the Great Plains.
3. The German yellowjacket, V. germanica (Fabricius), occurs throughout most of the United States except in the far south.
4. The southern yellowjacket, V. squamosa (Drury), is the most common southern species but its range extends northward to the Great Lakes and westward to central Texas.
5. The western yellowjacket V. pensylvanica (Saussure), is the most common and pestiferous in California and occurs primarily west of the Great Plains.
6. The aerial yellowjacket, Dolichovespula arenaria (Fabricius), is distributed throughout most of the United States.

BIOLOGY
Yellowjackets are social insects and live in nests or colonies. The adults are represented by workers which are sterile females, queens, and males which come from unfertilized eggs and usually appear in late summer.

Typically, only inseminated queens overwinter and do so in sheltered places. In the spring, she uses chewed-up cellulose material to build up a 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 varies from 300 to 120,000 cells, averaging 2,000 to 6,000 cells, and usually contains 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 are usually reared in old worker cells. The colony is then entering the declining phase. The newly emerged queens and males leave the nest and mate. Only the inseminated queens hibernate and survive the winter. The founding queen, the workers, and the males all die.

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. However, the German yellowjacket usually nests in buildings in the United States, the western yellowjacket occasionally nests in buildings, and 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. There are nest entrance guards to protect the colony. Yellowjackets are very slow to sting unless the nest entrance is approached and then they are quite aggressive. Each can sting a number of times, inflicting much pain. Some people become hypersensitive to their stings and future stings can become life threatening. Those nesting in or on buildings are only a problem when the nest or nest entrance is located near human activity. Overwintering queens may enter the living space during the winter seeking warmth, or in the spring when they are looking for a nest site or just trying to get back outside.

CONTROL
Yellowjackets are considered beneficial insects because their food consists mostly of various arthropods, often pest species. However, if their nest is located close to occupied buildings, recreational areas, or within structures, then control is warranted. During the day, locate where the nest entrance is for each colony to be controlled. Control should be done at night when most of the yellowjackets are in the nest. only background lighting should be used and a bee veil should be worn. If it is a ground nest, then dust an area for 6” (15cm) around the entrance hole with 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. In a day or so, the wall void nest area should be treated with a long-lasting, highly repellant material or else should be opened up and cleaned out to prevent future dermestid beetle, or spider beetle, and/or psocid problems. If it is an aerial nest, then an appropriately labeled aerosol works well.

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.