Yellowjacket wasps are common insects in Iowa that build annual colonies in the ground, or in holes in building walls and foundations. These inner-wall nests are often the source of wasps that will invade the living space within the house, especially in the fall and early winter.
In fact, yellowjackets in the house after the time of frost and the first freezing weather are almost certainly originating from a nest in a wall of the house. The nest has been in the wall since spring and the wasps spent all summer using a "front door" from the nest that lead outdoors into the yard where they fed on caterpillars and nectar. When the food sources disappeared after frost, and when it got cold out in the yard, the wasps turned to exploring the warm side of the wall and found a "back door" into the living space of the house. Wasps inside the house are often sluggish, but may be active enough to sting if the temperature is sufficiently warm.
Yellowjacket nests are annual, and the workers that comprise the majority of wasps within the nest all die with freezing weather. The annoyance of wasps emerging into the house is temporary, but heat from the furnace, warming the walls, keeps a very few of them alive longer than usual.
The practical control is to swat wasps as they emerge from the walls, and wait for the remainder to die of old age and cold weather. Spraying indoors is of little to no benefit. Plugging gaps where the wasps are coming through the wall would help but we almost never know where the nest is located or where the wasps are getting in. The problem will go away in time, certainly by the time winter "really" gets here. Yellowjacket wasps do not reuse a nest the following year and the wasps emerging inside the house will not establish new colonies nor reproduce during the winter.
This article originally appeared in the October 13, 1995 issue, p. 145.
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