Yellowjackets are very common at this time 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.
Yellowjacket 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 degree 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.
As with all bees and wasps except worker honey bees, yellowjackets can sting 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.
There are two common species of yellowjackets in Illinois. 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. German yellowjacket adults have a few tiny black spots on the upper side of the abdomen; eastern yellowjackets do not. Underground nests can be killed by flooding the nest with permethrin or other pyrethroid insecticide followed by a shovelful of soil. Nests inside walls can be killed by placing carbaryl as Sevin Dust in and around the eave opening so that the wasps get it on their legs as they come and go. Nests are best treated in the evening while there is still enough light to see without a flashlight. The yellowjackets will be less active but will fly at a light if disturbed. Wear protective clothing to avoid stings. If you have to do landscape maintenance near a yellowjacket nest, try to do it near sundown when the wasps are less active.
During the day, avoid yellowjacket stings while working by avoiding yellow clothes or those that contain yellow, such as pink or lime green. Bees and wasps are attracted to the yellow in flowers. Similarly, avoid perfumes and other fragrances based on flower odors. If a yellowjacket lands on you, blow or brush it away rather than swatting at it. If one gets under your shirt, take your shirt off, while being careful to avoid tightening the shirt and wasp against your skin. Realize that yellowjackets can sting through cloth, so squashing one under your shirt between your fingers is still likely to result in a sting. Yellowjackets commonly enter open soft drink and beer cans, so put beverages in cups outdoors so you can see what you are drinking. A swallowed bee or wasps can sting the throat, causing swelling and suffocation. Avoid handling dead yellowjackets because a dead one can sting until rigor mortis sets in.