Yellow jackets are highly social wasps, often mistaken for bees due to their bright yellow and black coloration. They live in annual colonies composed of a single queen and thousands of workers. Understanding their activity cycle is important because, unlike bees, they can sting multiple times and become aggressive when defending their nest or foraging late in the season. Their daily and annual cycles of inactivity are dictated primarily by temperature and the seasonal progression of the colony structure.
The Daily Cycle of Inactivity
Yellow jackets do not experience true sleep, but they become functionally inactive when temperatures drop and light fades. This daily cessation of activity is a state of cold-induced dormancy, allowing them to conserve energy. As ectotherms, these wasps rely on external heat sources to warm their powerful flight muscles.
Foraging flight generally ceases shortly after dusk and resumes around dawn. However, temperature is the major limiting factor, as workers typically become sluggish and stop flying when the ambient temperature falls below approximately $50^{\circ}$F. Peak activity occurs during the warmest part of the day when solar radiation is strongest.
If the temperature is too low, the wasp cannot generate the necessary heat to engage its wing muscles for flight. Workers retreat to the nest cavity during these inactive periods to rest and receive residual warmth from the collective activity of the colony.
The Annual End of the Colony
The seasonal cycle represents the end of the yellow jacket population, triggered by cold weather and resource depletion. Colony growth peaks in late summer and early fall, when the population swells to several thousand workers. The colony then shifts its focus from producing workers to creating new reproductive individuals: males and new queens.
This shift results in the cessation of larval production, which profoundly affects the workers. Adult yellow jackets feed on nectar for energy, but they rely on larvae to secrete a sugary substance in exchange for the protein the workers provide. When the last larvae pupate, this sugar reward disappears, leaving the workers hungry for carbohydrates.
Driven by this hunger, the workers become aggressive scavengers, seeking out human food sources like sugary drinks and ripe fruit. The colony’s final demise typically occurs with the first hard frost or after temperatures remain below $45^{\circ}$F for multiple days. At this point, the old queen, workers, and males perish as the colony structure breaks down.
How the Queen Survives Winter
The only members of the colony that survive the winter are the young queens. These queens leave the nest in the fall to find a sheltered location before the cold arrives. They enter a physiological state known as diapause, a form of hibernation that allows them to survive the winter months.
To endure freezing temperatures, the queen’s body produces cryoprotectants, often called “antifreeze” proteins, which prevent ice crystals from forming in their tissues. These solitary queens seek out protected sites like under loose tree bark, in hollow logs, or within cavities in man-made structures. They remain in a deep, inactive state until spring, relying on stored fat reserves to sustain their low metabolic rate. Once temperatures warm sufficiently, the queen emerges to establish a new colony, restarting the annual cycle.