By Laura Jesse
Plant and Insect Diagnostic Clinic
Iowa State University Extension
Yellowjackets are the fairly small yellow and black wasps you often see in the fall looking for food near garbage cans and nervous picnickers. Yellowjacket wasps are primarily meat eaters, but they have a sweet tooth, especially in the fall. I dislike them because they have a rather painful sting and I hate when they hover around me looking for food.
For instance, I was eating my turkey sandwich outside this summer and one rather impertinent yellowjacket flew over, landed on my sandwich and began chewing off a big chunk of the turkey. I am stuck holding the sandwich thinking that I would be least likely to be stung if I just let her get the turkey and go, and also wondering how dirty yellowjacket feet and mouthparts are, and if I should eat the rest of the sandwich or not. I did eat the rest of the sandwich which is a bit gross, but I have no ill effects to report.
Yellowjacket wasps build annual colonies in the ground, or in holes in building walls and foundations. Those ground nests are another way many unfortunate people come in contact with yellowjackets. Yellowjackets are aggressive and will defend the colony if you happen to stand too close. They also tend to get very angry when a lawn mower goes over their colony!
Nests built into wall voids or attics are often the source of wasps that 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 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.
Occasionally an old yellowjacket nest in the wall of a house will smell a bit the following year from the dead wasps inside, and other insects can get into the nests to feed on the dead wasps and then accidentally wander indoors. However, it is not necessary to remove yellowjacket nests within walls since any problems are more of a nuisance and temporary.
I often get asked “what is the purpose of an insect, what is the redeeming value?” In the case of yellowjackets they do consume many other pest insects such as caterpillars that eat our garden plants. I do always feel a bit bad for the insect when asked what its value is and wonder if one yellowjacket hovering over the garbage ever turns to another yellowjacket and asks “what is the purpose of humans, why are they here?”Although I suppose the other yellowjacket looks down at the garbage and says “to provide food for us!”
Laura Jesse, Plant and Insect Diagnostic Clinic, (515) 294-5374, firstname.lastname@example.org