MILWAUKEE— If it seems like yellowjackets are suddenly everywhere, there’s a reason and the time of year has a lot to do with it.
Dr. Chelsea Cook, an assistant professor of biological sciences at Marquette University, says an early and relatively mild spring likely gave yellowjacket queens a head start. Queens typically spend the winter sheltered in places like leaf litter beneath the snow before emerging in the spring to begin building their nests. Without a late cold snap to interrupt that process, Dr. Cook says colonies had more time to grow.
Now, as summer winds down, those colonies are reaching their busiest period. Worker yellowjackets are spending much of their time collecting food to support the colony as it produces reproductive females and males.
That makes late-summer cookouts and other outdoor gatherings especially attractive to the insects. Dr. Cook says yellowjackets are drawn to sugary drinks, meat and fermenting or decaying foods.
“They ​are, ​this ​time ​of ​year, ​really ​queued ​in ​on ​protein,” Dr. Cook said. “​So ​they’ll ​go ​after ​your ​steak, ​they’ll ​go ​after ​your ​burger. ​And ​the ​third ​thing ​is ​anything ​that’s ​fermenting, ​because ​that ​signals ​to ​them ​they’re ​actually ​decomposers. ​So ​part ​of ​what ​they, are ​interested ​in ​and ​want ​to ​eat ​are ​decaying ​apples, ​decaying ​fruit, ​decaying ​vegetable ​matter, ​and ​decaying ​protein ​matter.”
Dr. Cook says yellowjackets are attracted to all those types of foods, and that’s why people may notice more of them around garbage cans, outdoor meals and drinks, especially during late summer when the insects are at peak activity.
Despite their reputation, Dr. Cook says yellowjackets aren’t necessarily looking to sting people. They’re more likely to become more defensive when they feel threatened, particularly when someone gets close to a nest.
“I ​never ​want ​to ​advocate ​for ​the ​killing ​or ​harming ​of ​insects, ​but ​if ​you ​have ​a ​yellow ​jacket ​nest ​near ​your ​home ​and ​you’re ​being ​bothered, ​or ​your ​kids ​are ​being ​bothered, ​or ​your ​dogs ​are ​being ​bothered, ​then ​I ​give ​you ​full ​permission ​to ​call ​an ​exterminator,” Dr. Cook said. “​Don’t ​handle ​it ​yourself ​because ​it ​can ​get ​messy ​and ​dangerous ​really ​fast. Call ​an ​exterminator ​and ​get ​rid ​of ​them.”
Many yellowjacket nests are built underground, which can make them difficult to spot. Dr. Cook says mowing the lawn, making noise or creating vibrations near a nest can disturb the colony and lead to defensive behavior.
Yellowjackets may be a nuisance, but Dr. Cook says htye also serve an importatn purpoise in the ecosystem. They help break down organiz material by feeding on things like animal carcasses and rotting fruit, and they also act as incidental pollinators.
“They’re ​incredibly ​important ​to ​the ​ecosystem. ​I ​mentioned ​that. ​They ​are ​decomposers. ​So ​they ​are ​moving ​nutrients ​through ​the ​landscape,” Dr. Cook said. “​When ​they ​eat, let’s ​say ​a carcass ​on ​the ​side ​of ​the ​road, ​they’re ​getting ​rid ​of ​that ​for ​us. ​When ​they’re ​eating, the ​rotting ​apples ​at ​the ​orchard, ​they’re ​getting ​rid ​of ​that ​for ​us. You’ll ​see ​them ​on ​flowers, ​you’ll ​see ​them ​collecting ​pollen, ​which ​is ​a ​protein ​source. ​So ​they’re ​kind ​of ​incidental ​pollinators ​as ​well.”
Their numbers should eventually start to drop as temperatures cool. But Dr. Cook says yellowjackets can remain active for several more weeks before a hard frost brings their season to an end.
“The ​more ​warm ​weather ​we ​have, ​the ​more ​yellow ​jackets ​we’re ​gonna ​see,” she said. “​They ​only ​exist ​until ​the ​first ​hard ​frost. ​So ​we ​probably ​have ​a ​couple ​of ​months ​until ​that ​happens.”
