Send Letter to Editor

Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

A yellowjacket munches on an apple. Yellowjackets seek high-sugar foods for 'flight fuel'; high-fat protein foods (insects, carrion, or human foods like bratwursts) are brought back to the nest to feed the growing wasps. © Robert L. Jeanne
A yellowjacket munches on an apple. Yellowjackets seek high-sugar foods for 'flight fuel.' High-fat protein foods (insects, carrion, or human foods like bratwursts) are brought back to the nest to feed the growing wasps. © Robert L. Jeanne

October 2003

The gatecrasher in the loud yellow and black suit

When fall food and drink are plentiful, these wasps are ready to party.

Lee Clippard

Know thy enemy | Why do yellowjackets bother us so?
Evening the score

Come Saturdays in fall, folks from around the state swarm into Madison headed for football at Camp Randall. Cars line the neighborhood streets, red-clad crowds stream toward the stadium, and the distinct smell of tailgate-cooked brats and beer hangs in the air. But people aren't the only things swarming into the stadium on Saturday. Following those same smells are yellowjackets. When the game gets underway, there are plenty of shouts and cheers for the Badgers, but there are also a few yelps of pain when football fans come face-to-face with these pesky creatures.

Nancy Robinson, EMS Coordinator at Camp Randall, is well aware of the distress yellowjackets inflict. "On average, in August and September, the paramedics respond to two or three stings per game in the stands and about 16 patients will come into the first aid stations," says Robinson. The number of stings is likely higher, as football fanatics shrug off a sting to keep watching the Badgers push for the end zone. The yellowjackets are such a problem that between displaying touchdowns and field goals, the scoreboard flashes a reminder to fans: "Please make sure to check for bees in your beverages!"

Know thy enemy

While there's no real harm in calling a yellowjacket a "bee," it gives the true bees a bad rap. If there's an insect hovering around your soda can this time of year anywhere in Wisconsin, chances are it's a yellowjacket. Yellowjackets are actually wasps, distant cousins of the bees, as both belong to the scientific group Hymenoptera.

Thirteen different yellowjacket species reside here and all are recognizable as little buzzing bullets with angry faces. They aren't covered with fuzzy hairs like bees. Instead, they are slender and slightly shiny. Most yellowjacket species boast distinct yellow and black banding patterns on their bodies, but some species are actually black and white. One ubiquitous yellowjacket in Wisconsin, a member of the black and white camp, is commonly known as the bald-faced hornet.

That said, identifying a yellowjacket wasp is difficult, especially if you are running away from it as fast as humanly possible! Several flying insects are often mistaken for yellowjackets: honey bees, bumble bees, and paper wasps. Honey bees are cute, furry fliers that make honey, beeswax and pollinate about 80 percent of our important agricultural crops like apples and alfalfa. Since honey bees only collect nectar and pollen, they are rarely, if ever, interested in human drinks and foods. Honey bees will sting, but usually only when heavily provoked, like when you mess with their hive or accidentally step on a lone forager. Honey bees, with their yellowish brown fur and docile demeanors, seem like teddy bears compared to the yellowjacket clan.

Bumble bees, just as their name describes, are fat, fuzzy critters that buzz around from flower to flower, and when loaded up with pollen and nectar, return to their little colonies in the ground. Bumble bees are often confused with yellowjackets thanks to their coloration and because, like some yellowjackets, they too nest in the ground. To add to the confusion, many Wisconsinites have grown up calling "bumble bees" yellowjackets. This must come from the fact that bumble bees, with their typical black abdomens and pale yellow thoraxes, look like they are actually wearing a "yellow jacket."

Paper wasps are actually close relatives of yellowjackets. From a distance these slender, mostly hairless wasps resemble yellowjackets, but their nests are very different. Paper wasps build their nests on the warmer southern eaves of houses, and their homes aren't covered in paper – a habit for which yellowjackets are renowned.

A yellowjacket nest is one surefire way to distinguish the insect from all the other look-alikes. Even those who harbor hatred for the stinging fiends will admit that the yellowjacket nest is truly a beautiful work of architecture. Through a long process of scraping, chewing, mixing and building, the wasps create artful papery globes. The queen builds a small golf ball-sized honeycomb structure that is the core of a nest. Worker females add more paper, called carton by biologists, to expand the nest. The wasps manufacture the grayish carton by scraping up tree pulp and mixing it with their saliva. They apply this mixture in papery thin strips that form stacks of combs to hold vulnerable larvae and sheathe the nest in a very strong protective cover. Depending on the yellowjacket species, the nest will hang from a branch, nestle inside a cozy wall crevice, cling to the side of a house, or go underground concealed in a cavity. Whether underground or in the air, most people recognize these as the classic "hornet's nest." The yellowjackets work hard to create this amazing nursery and home base, yet it is only used for a few months each year then stands abandoned like a factory out of commission.

A yellowjacket colony, like the Fourth of July, is an annual event that goes out with a bang. Colony life begins in the spring. When the snow and ice are just finished melting away, plump hibernating queens emerge from their winter slumber in search of a nice place to start a family (i.e., chipmunk hole, rotting tree stump or tree branch). Once the young queen finds a suitable spot, she builds a tiny paper nest by herself and then starts laying eggs. These eggs hatch into all female workers that help expand the nest and raise more workers. The colony grows larger and larger through the summer, and by late August or September, some colonies can hold 3,000-4000 workers.

For people, wasps cause the most problems in early fall when the number of workers is so high. During reproduction time (the "bang" part of this cycle, which is typically September and October in Wisconsin), the colony starts producing males and larger females, destined to be future queens. When the new queens and males hatch, they fly away to mate. Afterwards, the males die, having served their lone purpose: insemination. The newly fertilized females, on the other hand, still have much to do before their biological role is filled: each new queen must find a snug place to hibernate over winter, while waiting to start a brand new colony in the spring.

Yellowjackets defend these great colonies using another unmistakable characteristic: their painful, powerful punch. When a bee stings, she sacrifices her life defending the colony. A bee's reverse-barbed stinger works like a bait-holding fish hook: it goes in but won't come out. On the other hand, a yellowjacket can sting again and again. This is why one wasp trapped in your shirt can get you multiple times. Since wasps aren't necessarily risking their lives to sting, they can afford to be a little jittery and aggressive. Yellowjackets will defend their nests from attack with a vengeance, but they will also defend themselves from attack (i.e., a mouth covering their soda can) when they are far away from the colony.

One wasp sting is painful enough. But get stuck with the thrust of an entire colony and you can end up in the hospital, or worse. The Centers for Disease Control in Atlanta report that 40-50 people die each year in the United States from allergic reactions to stings.

Why do yellowjackets bother us so?

Yellowjacket colonies survive by sending out foragers to scour the countryside for sweets and meats. The foraging wasps must collect enough sugar and protein to support the growing hordes of larvae, the busy workers, and eventually, new queens. To get their sugar fix, yellowjackets search out the sweet secretion of aphids and scale insects, called honeydew, which collects on leaves and branches as it falls from the sap-sucking insects. Hunting for other critters like caterpillars, spiders, centipedes, flies and damselflies provides the colony with protein. Foragers also sidle up to the bar with crows and vultures, and industriously carve away fleshy morsels from carrion with these other scavengers. And because yellowjackets are born to scavenge, they have one particularly profitable food provider: people.

As with other forms of wildlife, there is often a conflict between yellowjackets and people competing for the same space at a state park, a well-manicured back yard, or a county fair. Where people abound, the wasps may eschew the search for honeydew and take the easy pickings of soda or other sweets in garbage, at a picnic table, and in a cup in a hand on the 50-yard line. They'll happily pull pieces of turkey right from between the slices of bread on a plate or munch away on a Johnsonville brat as if it was beer-boiled and grilled just for them.

Nancy Robinson, EMS Coordinator at Camp Randall (l) attends to a Badger fan who was stung by a yellowjacket. © Robert Queen
Nancy Robinson, EMS Coordinator at Camp Randall (l) attends to a Badger fan who was stung by a yellowjacket.

© Robert Queen

"The thing that's always been interesting to me," says Camp Randall's Nancy Robinson, "is the number of people who get stung in their mouths while eating their brats." For these wasps, Camp Randall is an all-you-can-eat buffet. Robinson jokes that there are so many wasps around the stadium during August and September that they must "tell one another to come down on Saturday morning."

She's not that far off.

In 1998, Professor Bob Jeanne and Stephanie Overmyer at the University of Wisconsin-Madison confirmed Robinson's suspicion that some yellowjackets were in the know. Jeanne and Overmyer discovered that foragers of the German yellowjacket, an invasive species, somehow communicated to other wasps in their colony when there was sugar-water to be had. The researchers theorize it has to do with the odor of soda and other sweetened drinks. The means by which wasps recruit each other is still uncertain, but it's clear they can quickly communicate when and where food and drink might be discovered. Those spots can be rapidly overrun by yellowjackets.

The German yellowjacket is a special pain, simply because it lives in close proximity with humans. This onerous wasp invaded Wisconsin in the 1970s as it spread from Europe to eastern North America and westward. It's considered an urban pest because of its propensity for choosing walls and attic spaces for nesting, though it will also nest in the ground.

"If you go out on the UW-Madison campus during the fall and collect what's coming to your soda, I would guess that 95 percent of the insects will be German yellowjackets," Jeanne says. "Yellowjackets use soda and other sweet drinks as a sort of 'aviation fuel' to give them energy for flying and harvesting. The fats and protein they collect are brought back to the nest to nourish the larvae. That's different from the food mix wasps seek in the country," Jeanne says.

"Out in the rural areas it's still pretty much the same food sources native yellowjacket species have traditionally used." Jeanne said. In fact, one researcher working in Jeanne's lab found that yellowjackets coming to traps in the urban area were almost exclusively German yellowjackets. Traps in other parts of rural Dane County were dominated by the native Eastern yellowjacket. That's not to say yellowjackets are pests only in larger urban areas, but the concentration of people and wasps in larger cities likely increases negative encounters.

Evening the score

You may notice outdoor malls and gathering places around Wisconsin peppered with yellow traps marketed for yellowjacket control. They're filled with sugar-water and other specially patented chemicals that will attract the wasps. Most of them are chock-full of wasp corpses come October. But do they help?

Jeanne says those kinds of traps thin out the worker population, "but you don't kill the colony." He estimates that for every 100 yellowjackets killed from a colony, the queen may produce 200-300 more wasps. "Killing a few thousand yellowjackets at a trap over the course of the summer isn't going to make a dent."

Traps won't likely solve any problems for you in September, but traps set out in early spring could attract enough queens searching for sugar to put a dent in the summer's yellowjacket population.

If a wasp colony isn't bothering anyone, the best thing to do is let it be. By the time the first freeze descends in fall, the colony will have sent out its reproductive males and females and will be at the end of its life. All the workers will die and nests, whether in trees, walls or underground, are generally not reused. After a hard freeze or two is the perfect time to collect old nests and donate them to a local science class.

Yellowjacket nests also can disappear naturally with a little help from raccoons, badgers and skunks that seek out the larvae. To these animals a nest full of yellowjacket larvae is one giant, juicy protein-packed lunch.

If the colony is wearing your nerves thin and the fall freeze seems too far away, the best way to get rid of the nest is to sneak up at night. The yellowjacket defense team is inactive below 50F. Wasp nests can be quickly bagged in heavy plastic, frozen, left in the sun or poisoned with commercial wasp and hornet sprays. The safe bet is just to leave it alone. Definitely don't try covering a ground nest hole with a rock or plugging a hole in the wall with caulk. Wasps are extremely diligent and will quickly find a new way out of the nest cavity, either by digging a new hole or by coming into your house.

For more specific recommendations about control techniques, check out UW Department of Entomology, or send for the UW-Extension bulletin A-2018, "Wasp and Bee Control," by Jeffrey Hahn, Phil Pellitteri, and Donald Lewis.

Whether you're picnicking, at a football game or just relaxing with an afternoon beer by the lake, the best advice is simple vigilance. Bob Jeanne echoes the warnings of the Camp Randall scoreboard, "If you're just going out to a state park and opening up a picnic basket there's really not much you can do. Just be careful that you're not the only one drinking out of your soda can." And don't forget to check your brats, too.

Lee Clippard is a freelance science writer based in Madison.