Yellowjackets are very common throughout the state. These are the 1/2-inch-long, yellow-and-black-banded wasps that are very numerous around garbage cans and picnics. Many people call them bees, but honey bees are 1/2 inch long, with black and amber to brown bands.
There are two common species of yellowjackets in Illinois. Both species build underground nests, but the eastern yellowjacket tends to nest underground in abandoned rodent burrows. The German yellowjacket tends to nest inside the walls of buildings, typically entering through an opening in the eaves.
Yellowjacket adult queens overwinter under loose bark and in other protected areas. They emerge in the spring to start their nests, typically underground or in a building wall. The nests are made of paper, which the wasps construct by scraping the surface wood off dead tree limbs and unpainted fences, mixing it with their saliva and applying it into place with their jaws. Their nests are similar in construction to the football-sized and -shaped nests of their close relative (the baldfaced hornet) found hanging from tree branches.
Through the summer, several generations of wasps are produced, with the adults foraging for caterpillars and other forms of meat to feed the legless, grublike larvae in the nest. The adults feed on flower nectar and other sweet liquids. As fall approaches, larval production ceases, and the mainly adult population switches from a single reproductive queen with numerous sterile female workers to a queen, workers, males, and reproductive females. The males and reproductive females mate, the males die, and the newly mated females find overwintering sites.
The old nest is left with an old queen and about 2,000 workers seeking flower nectar as food. As fall approaches, flowers near the end of their seasonal cycle and cease to bloom, greatly restricting food for a very large yellowjacket population. Once it freezes, blooming ceases. The result is a very large, very hungry population of wasps that are short-tempered and sting with little provocation. These wasps do not die until there is a 5- to 7-day period when the high temperature is below 45°F. They search out every nook and cranny for food, including those on humans. If one is on your neck or inside elbow and you turn your head or flex your arm, you are likely to pinch the yellowjacket’s leg or body in a fold of skin, resulting in the yellowjacket stinging you immediately.
Disturbed nests are strongly defended, with each female wasps typically stinging repeatedly. Not only is the sting painful, but it can be life threatening. Sensitive individuals can enter anaphylactic shock and die from a single sting. Annually, 40 to 50 people die in the United States from yellowjacket stings.