Yellowjackets (Vespula spp. and Dolichovespula spp.), Baldfaced Hornets (D. maculata), and Paper Wasps (Polistes spp.) belong to the wasp family, Vespidae. These wasps share many traits including defending their nest at all costs and an ability to sting multiple times without dying.

Their stingers, which are modified ovipositors (ovi=egg; -positors = to deposit), lack barbs meaning they can jab and inject venom over and over again. Indeed, nest defense and multiple stings are connected.

On the other hand, these wasps are considered significant beneficial insects by providing a twofer. They are pollinators as well as predators of soft-bodied insects including caterpillars and sawfly larvae. Many of their food items are significant plant pests.

Despite their belligerent reputations, paper wasps, yellowjackets, and baldfaced hornets are seldom aggressive away from their nests. There’s simply no benefit in wasting energy chasing after people far from home base.

Of course, nest defense is a different matter. Painful meetings between these wasps and people most commonly involve an accidental or deliberate incursion by a person into the “nest defense zone.”

Accidental encounters are particularly common with subterranean yellowjacket nests. However, baldfaced hornet nests may be hidden within plant foliage which also presents a risk.

European paper wasps (Polistes dominula) look like a cross between a yellowjacket and a paper wasp. Unlike our native paper wasps, these non-natives commonly build nests in unexpected locations including inside plants, particularly in conifers. The locations present a higher risk to gardeners and landscapers compared to our native paper wasps which tend to build nests under the protective eaves of homes and other structures.

Of course, intentional encounters with paper wasps, yellowjackets, and baldfaced hornets aimed at waging war on these beneficial insects is a particularly high-risk endeavor. We're woefully outclassed because these wasps have been defending their nests for hundreds of thousands of years. They have excellent eyesight and are programmed by Nature to execute several effective defense-attack strategies.

For example, baldfaced hornet nests commonly include a “back door” primarily used for ventilation. However, the second opening also means that while an attacker focuses on the front entrance, hornets bent on arriving with bad intentions stream out of the second exit. Paper wasps commonly power dive onto nest threats and yellowjackets will land and crawl into clothing to deliver their painful stings.

Nest avoidance is the best option to avoid stinging confrontations. I've taken pictures in several parks over the years of signs posted near an underground yellowjacket nest alerting the public of the yellow-and-black threat.

A sign isn’t needed to alert people of a large baldfaced hornet nest located next to a home entrance. Although yellowjackets, paper wasps, and baldfaced hornets provide significant environmental services, those services should not supersede human safety.

Personal safety should also be applied to nest elimination. Suffering a mass attack is not a good time for people to learn if they are allergic to wasp venom. A nest that threatens human safety should be eliminated by a professional.

Did Nests Just Suddenly Appear?

This is the time of the year when wasps expand their nests at an exponential rate. The nests have been with us since the beginning of the season; however, the wasps were flying below our radar owing to small nests containing few individuals.

Wasps spend the winter as fertilized females (queens) in protected locations such as beneath bark, inside hollow trees, etc. As spring temperatures warm, the queens leave their overwintering quarters to find suitable sites for nest construction.

The overwintered queens use their powerful mandibles to grind up fibers gathered from dead wood and plant stems which they mix with their saliva to extrude water-resistant paper used to construct their nests. This construction technique continues to be used by the queen’s offspring throughout the spring and summer.

Early wasp nests are relatively tiny structures. The elongated nests created by a baldfaced hornet queen may measure no more than 1 1/2" long. She gets help as her offspring complete their development which takes around 20 – 25 days in the Midwest.

This single dominant queen receives even more help once subordinate queens develop. Collectively, they lay more eggs that lead to more workers that lead to larger nests that lead to more eggs … etc., etc. By mid-to-late August, the nests become large enough to be noticed, or not; sometimes painfully.

However, even the largest wasp nests are only used for only one season. Eventually, the nests give rise to new queens and males (drones). Once the new queens are mated, they fly to their overwintering sites leaving the workers behind to meet their freezing fate.

Good Behavior

Paper Wasps, yellowjackets, and baldfaced Hornets are beneficial insects. Wasps are significant predators owing to their need to provide protein to the legless, helpless larvae awaiting food delivery in the nests.

The wasp workers forage for caterpillars, sawfly larvae, and other soft-bodied insects from late spring through the summer. They use their powerful mandibles to grind up these protein-rich meat items to feed to their larvae so they will develop into new adults.

I once watched yellowjackets decimate a colony of redheaded pine sawflies (Neodiprion lecontei) with the sawfly larvae being carried off one at a time to become meat items for yellowjacket larvae. I've also observed bagworm (Thyridopteryx ephemeraeformis) bags ripped open by baldfaced hornets to extract the caterpillar meat morsels inside.

Paper wasps, baldfaced hornets, and occasionally yellowjackets also provide the added benefit of serving as plant pollinators. They will visit flowers to feed on energy-rich nectar to support their predatory foraging and wood fiber gathering flights. "Pollinator gardens” (a.k.a. butterfly gardens) are a rich location for photographing these wasps.

Bad Behavior

Unfortunately, yellowjackets and baldfaced hornets have a deserved reputation for becoming serious nuisance pests late in the season. Once the drones and new queens complete their development in late summer to early fall, they do not need protein; they need energy from carbohydrates.

The royal newcomers lounge around the nest begging the workers for sweets. To appease these freeloaders, the workers search for foods that provide an energy boost such as soda, donuts, funnel cakes, and adult beverages. There are few things scarier than being chased by drunken belligerent baldfaced hornets decked out in their black leather jackets.

Another form of nuisance behavior is seen when these wasps visit hummingbird feeders. Although hummingbirds are highly aggressive in protecting their sugar source, they are occasionally driven off by interloping stingers.

Yellowjackets, baldfaced Hornets, and paper wasps will also seek a sweet treat in the form of honeydew exuded by plant-sucking insects such as aphids and soft scales. You may find these stingers on wasp galls where they serve as a security detail against gall predators in return for nectar exuded by extrafloral nectaries.

Yellowjacket traps are sometimes deployed to reduce the number of stingers arriving to spoil a picnic or drive customers from food trucks. However, research has shown that trapping can be problematic with careful positioning required to avoid enhancing rather than reducing a yellowjacket challenge. Even then, traps may not overcome the allure of rows of county fair concession stands offering scrumptious goodies best consumed after, but not before, a cholesterol test.

The most effective approach to managing yellowjackets and baldfaced hornets intent on crashing picnics, county fairs, and other outdoor gatherings is to remain diligent with trash collection. Overflowing trash cans is like a flashing neon “eat here” sign to these wasps.

Questionable Behavior

European paper wasps present a conundrum. The literature notes these wasps were first found in North America in the 1970s near Boston, MA. They are now found throughout much of the U.S. and parts of Canada.

Like their U.S. counterparts, these wasps are pollinators. They also forage for meat in the form of caterpillars and sawfly larvae to feed their young. However, they are highly aggressive meat-eaters and will readily spirit away monarch butterfly (Danaus plexippus) caterpillars.

Paper wasp stings are painful. However, stings by European paper wasps are even more painful because research has shown a correlation between their conspicuous warning coloration (aposematism) and the volume of their poison gland.

European hornets were first found in the U.S. in New York State around 1840. Since that time, the hornets have spread to most states east of the Mississippi and a few states to the west. European hornets are impressively large, measuring 1 - 1 1/4" in length.

Like our native vespids, they will grind up soft-bodied insects to feed their young. Unlike our natives, European hornets practice unusual plant-damaging behavior. They strip bark on the twigs and branches of trees and shrubs. It is speculated that European hornets are extracting sugar from the phloem tissue. The hornets will feed on a wide range of trees and shrubs including dogwood, lilac, and viburnums as well as ash, birch, boxwood, horse chestnut, and rhododendron.

Selected References

Balduf, W.V., 1954. Observations on the white-faced wasp Dolichovespula maculata (Linn)(Vespidae, Hymenoptera). Annals of the Entomological Society of America, 47(3), pp.445-458.

Miller, C.D.F., 1961. Taxonomy and distribution of Nearctic Vespula. The Memoirs of the Entomological Society of Canada, 93(S22), pp.5-52.

Braband, L., M. Frye, J. Lampman, D. Marvin, and R. Parker. 2016. Yellowjacket Trapping Efficacy Trials, NYS IPM Program, 2014-2016.

Day, E.R., 2009. European Hornet: Hymenoptera, Vespidae: Vespa crabro germana. Virginia Cooperative Extension, 2911-1422

https://vtechworks.lib.vt.edu/bitstream/handle/10919/50316/2911-1422.pdf

Vidal-Cordero, J.M., G. Moreno-Rueda, A. López-Orta, C. Marfil-Daza, J.L. Ros-Santaella, and F.J. Ortiz-Sánchez. 2012. Brighter-colored paper wasps (Polistes dominula) have larger poison glands. Frontiers in zoology, 9(1), pp.1-5.

Grissel, E.E., and T.R. Fasulo. 2013 (revised). Common name: yellowjackets and hornets, scientific name: Vespula and Dolichovespula spp. (Insecta: Hymenoptera: Vespidae). Featured Creatures, Entomology & Nematology. FDACS/DPI, EDIS, UF|IFAS. Publication Number: EENY-81

https://entnemdept.ufl.edu/creatures/urban/occas/hornet_yellowjacket.htm

Oliver, J.B., P.J. Landolt, N.N. Youssef, J.P. Basham, K.M. Vail, and K.M. Addesso. 2014. Trapping social wasps (Hymenoptera: Vespidae) in nurseries with acetic acid and isobutanol. Journal of Entomological Science, 49(4), pp.352-368.

Baker, A.M. and D.A. Potter. 2020. Invasive paper wasp turns urban pollinator gardens into ecological traps for monarch butterfly larvae. Scientific Reports, 10(1), pp.1-7.

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