WHO ARE THESE YELLOWJACKETS AND WASPS? “Wasp” traditionally refers to any member of the hymenopteran family Vespidae, a group that includes hornets, yellowjackets, “paper wasps” in the genus Polistes, and an assortment of other, mostly tropical, social wasps that live in social colonies and usually make their nests of paper. The word originated from the Anglo Saxon word root “webh,” meaning to weave, a reference to the “weaving of wood fibers” to make the paper of their nests. Today, in Europe “wasp” refers to hornets (Vespa) and their diminutive versions (Vespula, Dolichovespula). Oddly, in the United States, the word “yellowjacket” is commonly used instead of wasp for Vespula and Dolichovespula. As if more is needed to make one’s head spin, Americans single out the largest yellowjacket species and give it the name “baldfaced” hornet. That is, unless one is an American physician, in which case the favored name for the species is “white faced” hornet. All this seems rather silly, given that the species (Dolichovespula maculata) is neither a hornet (any wasp in the genus Vespa) nor does it have either a “bald” (whatever that might mean here) or a “white” face. Americans and American physicians are not the only people to add naming confusion. Scientists have contributed their part. The most abundant yellowjacket species in most of the western United States, especially west of the Rocky Mountains, was named in 1857 by the Swiss-born Henri de Saussure as Vespula pensylvania. He got it wrong on two fronts. First, Pennsylvania was a large well-recognized United States eastern state, and the name was universally associated with that part of the country. Second, he misspelled “Pennsylvania,” leaving out an “n.” The second mistake could be forgiven, as de Saussure was neither an American nor an Anglophone, and he simply might have made a typographic error, or have been unaware of the correct spelling of William Penn or Pennsylvania. The first mistake is harder to forgive, as de Saussure confused combined species taken from eastern Canada and from western Mexico, giving the mixture of species the name “pensylvania.” Neither set of specimens came from Pennsylvania, leading one to wonder where the pennsylvania (or pensylvania) came from. To add more flavor to the confusion, Joseph Bequaert in 1931, while attempting to clarify the mess listed the name as “pensylvaniva” (“v” emphasized), clearly a typographic error, but one permanently in the record.2 The net result is that to this day the name causes both spelling and distribution problems in the literature. No wonder the best name for the species might be its official common name: the western yellowjacket. In the spirit of facilitating communication, this writer will use the word “yellowjacket” to specify the combined genera Vespula and Dolichovespula, “hornet” to specify Vespa, and “wasp” for any social wasp, including yellowjackets and hornets.
Yellowjackets and hornets are large, often shiny insects sporting coats of yellow or white on black, sometimes splashed with reds, oranges, or browns. They mostly have an annual life cycle in which a single individual, a fertilized queen, founds a colony alone. Later in the cycle the queen becomes an egg-laying machine, leaving her offspring, the workers, to do most of the work. The cycle starts with males and young queens that usually fly out of the colony to mate. Depending on the species, mating is a short-lived activity, lasting anywhere from 10 seconds to 10 minutes, which looks to the human observer as awkward, rather than the frenzied sex of fire ant matings. The male mounts the female from behind, engages genital fixation, and then falls backward, often dangling from the female. Both males and females mate multiple times, averaging over five and nine times for two studied species.3
Once mating is complete, the new queens fatten themselves, while the not-so-lucky males die (being a male insect can be tough). In temperate-climate species, each female then locates a protected area, often under tree bark, within decomposing forest litter, or within crevices in buildings to “hibernate” through the winter. Months later, after using up to 85 percent of their fat stores,4 queens emerge from overwintering and start new colonies. The queen’s first goal is to find a preferred nest site: an abandoned rodent burrow, some other hole in the ground, a nice location in vegetation, a hollow tree, or a space in the wall of a home. Once the queen locates her nest, she makes hexagonal paper honeycomb cells from chewed wood or plant fiber, lays an egg in each cell, and surrounds the whole with a paper envelope. When eggs hatch, she forages from her nest to obtain prey to feed the larvae. As the young grow, the queen will often curl around the thin pillar-like pedicel from which the nest is attached and warm the young to speed their maturation. If all goes well, in a few weeks, young workers will emerge, take over most of the work duties of foraging, collecting pulp and water, and enlarging the nest, and bring the colony into the rapid growth phase.
Often, all is not well. A queen may covet the successful nest of another queen. Why make your own nest if you can steal someone else’s? Other queens will try to invade and take over (usurp) the host queen’s colony, often killing the queen in the process. These usurping queens can belong to the same species or to another species.
One well-studied example is the eastern yellowjacket, Vespula maculifrons, and the southern yellowjacket, V. squamosa, in which the larger southern yellowjacket queen prefers to take over a nest of her eastern sister. Not that she can’t make her own colony—she can; however, she prefers to pilfer the work of another. These usurpation battles can be violent. Often a series of separate invasions result in multiple dead queens, stung to death and found under the nest or in the entrance. Odds for survival can worsen for the new queen. She can be invaded by another species, a full social parasite, that is unable to found her own nest or even to produce workers. These cuckoos have a real advantage over the original queen. They are usually stronger, with harder body integuments and larger, more curved, stouter stingers. Their venom is not more powerful,5 but their stings are better able to find their mark on the host queen. The host queen usually fatally loses.
If the queen makes it through the colony founding stage, and 90 percent don’t,6 the colony enters the growth phase. Food, fiber, and foraging take center stage. The queen’s newly reared and reproductively sterile workers now forage distances within 400 meters from the colony, sometimes up to 1,000 meters,7 where they seek their resources: water, nectar, fiber, or prey. Water is needed to manufacture paper or to cool off in hot weather. Nectar from flowers, honeydew sources, fruit, or soft drinks (“Coca-Cola wasps”) is needed to fuel their energetic flight or for warming the nest. Fiber is needed to enlarge the nest by adding more paper cells or protective envelope coverings. Different species have different favorite fiber sources. Some prefer weathered sound wood, as from the gray burnish on the clothespins in my backyard, others prefer rotting, punky fiber sources. The latter paper produces fragile, trashy paper that easily crumbles, much to the chagrin of collectors hoping to attach a wasp nest trophy to their wall. Prey foraging is the most difficult task for a worker. She must first locate a suitable prey or other protein source, such as carrion. Then she must catch it (carrion excepted), subdue it, process it to be suitable to carry, and fly back with her prized meatball to the nest. Favorite prey include flies, especially houseflies, stable flies, horseflies, or other common flies and caterpillars, but most any insect or spider prey will do. The list reads like an inventory of small life: moths, grasshoppers, cockroaches, cicadas, beetle grubs, bees, spiders, and even other yellowjackets of the same species.8,9 Large life is not excluded from the diet. Yellowjackets have been known to forage for flesh from horses’ open wounds.10 One particularly intrepid entomologist recorded notes of a yellowjacket carving a hole in his ear lobe and flying off with a drop of blood in its mouth.11
Wasps forage both visually and olfactorily. Their large compound eyes are better suited for detecting movement than for forming sharp images. If a prey moves, it is detected and pounced on; if the prey does not move, as in a sitting fly on a barn wall, the wasp will pounce on it anyway. Imagine the frustration of a yellowjacket repeatedly pouncing on nail heads on barn sides that look like resting flies. To its credit, a yellowjacket
learns that a nail is not a fly and does not pounce on it again. It, however, pounces on other nearby nailheads, having to learn each time that this black spot is not a fly.8 Odor is the other main cue in foraging. Yellowjackets are often seen flying upwind to a food source. If the food source is too large to be carried home in one trip, a yellowjacket will make an orientation flight in which it hovers while facing the source and arcing from side to side while progressively moving away from the location. With this method, the forager visually learns the location of the bounty, whether it is the remnant of a large spider, a dead mouse, or a partially eaten jelly sandwich, and can quickly return for its next morsel. Yellowjackets also recruit fellow nestmates to a food source by transferring the food odor to other yellowjackets in the nest. Armed with the odor cue, these yellowjackets head out and search for the odor source and visually for other yellowjackets already feeding on the source.12
As the yellowjacket colony grows from a small queen colony to a large, populous colony, it changes from a factory that produces only workers to one that produces reproductive males and queens in addition to essentially sterile workers. This shift usually occurs in late summer and autumn, when the colony is most populated. Like having a house full of teenagers preoccupied with the other sex, life in the yellowjacket colony is more chaotic when the new reproductives arrive. They do not work, but they demand and eat food. The colony begins its decline, often with the queen mother disappearing and the workforce shrinking. By the end of the season, all workers have died, the new queens have mated, and the males have died. So ends the annual cycle, as the nest is abandoned, and the new queens seek their refugia for the winter.
But, wait. This is not always the story. In warmer parts of their range, a few biannual colonies of some species overwinter into the next year. These polygynous colonies, with multiple functional queens, continue to grow unabated. Colonies sometimes have more than 100 queens,13 grow to 3 meters high and 1 meter in diameter,14 and weigh 450 kilograms.15 Young children might be advised not to throw rocks at these colonies.
Rock-throwing children are not the only “predators” of yellowjackets. Yellowjacket predators come in all sizes. Small predators include robber flies (Asilidae), spiders, and dragonflies. Robber flies and dragonflies catch individual foraging queens, workers, or males while on the wing. Robber flies grab the forager and punch through the neck or top of the thorax with their stiletto mouthparts and inject a powerful, nearly instantaneously lethal venom. Dragonflies swoop onto a flying wasp, hold it in a basket formed with their six legs, and quickly chew through the wasp’s body. Web spiders prey on yellowjackets caught in their webs, while crab spiders cryptically hide in flowers and grab individuals as they land on the flower, seeking nectar.
Large predators include a variety of birds and mammals. Mice, moles, and shrews commonly predate hibernating queens. Large mammals pique human interest more than mice and moles; they also are more serious predators of yellowjackets, often destroying fully mature and populous colonies. In Great Britain, badgers are particularly important.15 Once, while they were excavating a yellowjacket colony in a Wisconsin backyard, Jenny Jandt and Bob Jeanne, two talented yellowjacket experts, watched a large raccoon sitting on the back porch. The raccoon, in turn, was watching them in apparent anticipation of a future meal of yellowjacket nest scraps that might be left behind. (Little did it know that Jenny and Bob would leave no scraps.) Although this raccoon was unsuccessful in getting a meal, raccoons are considered the most important predators of underground yellowjackets in eastern North American, where they avidly excavate the nests, scatter the combs, and eat the brood from the combs much like a person eating corn on the cob.16 In Britain, other large predators include stoats and possibly weasels, whereas in North America, skunks, badgers, and black bears can be important predators in regions where these animals are abundant. Exactly how large predators endure yellowjacket stings is unclear. What is clear to humans is that yellowjacket stings really hurt. Do these animals have tough enough skin and dense enough fur to prevent stings? This seems unlikely, especially around the eyes, nose, and mouth, where skin is thin and hair is short. I once counted 3,305 honey bee stings in a German shepherd. Ninety percent of these stings were on the face, especially around the eyes and muzzle.17 I would be surprised if stinging yellowjackets were less able than honey bees to deliver a stinging message. Bears, famous in cartoons for their love of honey, have an equal love for yellowjacket protein-rich grubs. This love apparently transcends sting pain, as described by N. K. Bigelow in 1922: “A nest in the ground they will scratch up, digging with much rapidity, but often having to stop from the stings of the enraged insects. They will snarl and roll on the ground and go at it again. Although the punishment is severe Bruin keeps at it until he has secured his hard earned prize.”18
Perhaps bears, badgers, raccoons, and skunks are simply tougher and better at enduring stings than humans. Perhaps they are simply hungrier. Maybe they are resistant to venom, able to neutralize its effect like a mongoose neutralizes the effects of cobra venom. We still don’t know the answers to these questions. Stay tuned!
Birds are also important predators of yellowjackets and other stinging insects. A variety of birds, including Eurasian blackbirds, great tits, and kingbirds, will take yellowjackets in midflight. Another group of birds is so good at predating bees and wasps on the wing that they are called bee-eaters. The European bee-eater, Merops apiaster, catches a flying wasp, beats it against a branch to purge its venom, and then down the hatch it goes. If it’s a male wasp, the bird dispenses with the venom-removing operations and directly consumes it.19 The peculiarly named honey buzzard (Pernis apivorus), a large Old World bird, specializes in eating stinging insect prey. It has a delicate beak and is not closely related to hawks (Buteo) and certainly not to vultures, commonly called buzzards in North America. Honey buzzards are fond of yellowjackets and other stinging insects. The bird appears casual in its excavation and consumption of larvae and pupae taken from nests. It seems unconcerned with swarms of yellowjackets surrounding its head and shows no sign of bee stings. The bird seems more preoccupied with looking for its own predators and enjoying its meal.
If a variety of large, medium, and small predators prey on yellowjackets, what, then, is the value of the sting? Is the sting simply useful for killing or paralyzing prey? The brief answer to the first question is that the sting is a marvelous defense against most potential predators. The exceptions to the effectiveness of the sting as a defense alert us to how evolution is constantly honing predatory adaptations, strategies, and defensive behaviors. Exceptions also allow us to appreciate the usual value of the defense. Focusing on the success of a defense, though often less glamorous than the failures, is crucial to understanding the organism’s life.
Answers to the question, Do yellowjackets sting their prey? have filled the literature with anecdotes, poor observations, and careless oversights. Common sense tells us wasps should sting prey, but common sense is a tricky thing. Quoting my high school physics teacher: “Common sense is a very uncommon thing, because so few people have it.” Common sense easily biases our observations. Some classic reports that claim or suggest prey are stung include an early, particularly brash statement by F. M. Duncan in 1911: “It is chiefly as a means of procuring the necessary animal food for her young that the mother wasp uses her sting. … [Flies are killed by] repeated stab of the wasp’s sting.”8
Others were more cautious and concluded that the sting is used for large, powerful prey. These authors include Phil Rau: “Another [yellowjacket] was seen to sting an adult [grass]hopper, follow it in its agonized flight, and sting repeatedly until lost from view.”20
Phillip Spradbery wrote: “Only in rare instances does the wasp use its sting when grappling with prey and then only when it is particularly large or struggles sufficiently to free itself from the wasp’s grasp.”15
When precedents based on hasty or poor observations find their way into the literature, they become imposs
ible to eliminate. Other common themes in sagas of stung yellowjacket prey relate to dangerous prey. These include tales of yellowjackets and bees: “[The wasp] always trying for the head grip, thereby keeping the bee on its back. As soon as the bee was tiring the wasp became more aggressive, holding on with its legs and stinging it in the thorax.”21 And “after stinging it [a honey bee] several times between segments and biting it severely, the hornet carried it away to devour at leisure.”22
Further examples involve wasps stinging dangerous opponents: a wasp entangled in a spider’s web stings the spider;23 a wasp initially captured by a dragonfly turns the tables, stinging the dragonfly and treating the stung dragonfly as prey.24 In an observant discussion in reference to a yellowjacket capturing a fly, F. J. O’Rourke writes: “The wasp using its sting vigorously but at random,” and continues with “when it got on top of the fly it used its sting more vigorously while, at the same time, it chewed the interval between the head and thorax of the fly … [and] killed it, not by means of the sting, but by sawing off her victim’s head.”25
The Sting of the Wild Page 10