Yellow jackets are most likely to attack in the fall, but these stinging wasps are a year-round threat, especially because they can be hard to detect until they are disturbed; most often found while mowing the yard or pasture. Air traffic during feeding times will aid you in locating nest; be cautious there is always an escape hatch allowing guards to sneak up on those trying to disturb or kill a nest. If you dig one of these nests up, you’ll find it is a bulky, multi-tiered paper nest; commonly the size of a basketball, but well established nests can be much larger.
The name "yellow jacket" refers to several wasp species from the genus Vespula and Dolichovespula that typically have a yellow and black banded abdomen, commonly mistaken for European Honey Bees. Some of the most common yellow jackets found in North America are the Eastern yellow jacket (Vespula maculifrons), the Southern yellow jacket (Vespula squamosa) and the Western yellow jacket (Vespula pensylvanica).
Yellow jackets are small wasps about 3/8 inch long. Their black and yellow-banded bodies have three segments. Each insect is equipped with a smooth stinger that can sting multiple times; contrary to the European Honey Bee that ends it's life stinging only once with a barbed stinger that stays in the wound. Ground-nesting yellow jackets construct paper nests that may contain thousands of larvae and adult workers. These nests are typically located underground in abandoned rodent burrows or in other enclosed spaces such as tree cavities, wall cavities, wood piles, and dense ivy.
During the fall, young queens mate and find protected areas (such as fallen logs, tree cavities, cracks in buildings, etc.) where they remain for the duration of the winter. When spring arrives, queens select nesting sites and begin the process of colony initiation (nest construction, deposition of eggs, and hunting for food). Once adult workers emerge, they take over many of the tasks of nest maintenance so that the queen can remain within the safety of the nest and lay eggs. Foraging ground-nesting yellow jacket workers commonly come into contact with people who are eating outdoors and may become extremely aggressive. The colony grows throughout the summer and into fall, and eventually begins production of males and queens. When rain and/or freezing temperatures return, males typically die off leaving queens to start again next year, and newly mated queens find protected areas to overwinter so the process can begin anew in the spring.