By Melissa Fischer, Northeast Region forest health specialist, Washington State Department of Natural Resources, firstname.lastname@example.org
As many of you may have noticed, there were a lot of angry wasps flying about this past season. I was stung on multiple occasions while working in the woods.
I really thought I was going to get away with not stepping on a nest this year, but those hopes were dashed in late fall after I stepped on one over in Loomis State Forest. One of those stings left a welt unlike any I’ve had before (Image 1).
I am originally from Pennsylvania and was quite surprised at how aggressive the yellow jackets are here in Eastern Washington. I’ve been stung plenty of times in Pennsylvania, but not aggressively hunted in the woods as I am here. I also noticed that in some years (2015, 2018), yellow jackets seem more numerous and extra-aggressive. Wasps are not a focal insect for forest entomologists. I found myself curious as to why they are so aggressive some years and not others, so I decided to do a little research …
What are wasps?
Wasps are insects in the order Hymenoptera, which also consists of ants and bees. The wasps we will focus on are in the family Vespidae.
Sometimes people refer to wasps as bees, but they are not actually bees. Although the two have some similarities, they also have some significant differences. Some species of both wasps and bees are social; they live and work together, and both wasps and bees can be beneficial pollinators. Unlike bees, wasps are also predators and scavengers, killing pestiferous insects such as defoliating caterpillars and house flies.
Bees and wasps both consist of species that are capable of stinging. Only females sting though, as the stinger is actually a modified ovipositor (body part used to deposit eggs).
Although bees and wasps may have a similar morphological appearance, bees tend to be more hairy and stocky, whereas wasps are shiny, have much less hair, and have slimmer bodies with a petiole or “waist” (Image 2). Many species of wasp build paper nests from wood pulp; bees build their nests from a waxy substance. There are no wasp species that produce honey.
There are several species of wasp in Washington, the most aggressive of which are yellow jackets. Yellow jackets are about half an inch long, they are black and yellow, and feed on insects and sweet nectar. Although most people think of yellow jackets as one particular species, there are actually several, including the common (Vespula vulgaris), western (Vespula pensylvanica), aerial (Dolichovespula arenaria) and German (Vespula germanica) yellow jacket.
Aside from some morphological differences (Image 3), there are also some differences in the nesting habits of these yellow jacket species. The western and common yellow jacket build papery nests located underground. The aerial yellow jacket builds small, round papery nests above ground (Image 4). These nests are commonly located on roof overhangs and other protected exterior building surfaces.
The German yellow jacket, which was introduced into the northeastern U.S. in the 1970s and arrived in Washington in the 1980s, build above-ground nests as well, but they are not round, they are typically larger than that of the aerial yellow jacket, and they are often located within wall voids or attics.
Similar to bees, paper wasps are often mistaken for yellow jackets. They are morphologically similar to yellow jackets with black and yellow coloration, very little hair, and slim bodies, but there are some noticeable differences.
Paper wasps tend to be slightly larger (about three-quarters of an inch long) and slimmer, and rather than black on the upper side of the antennae, they have orange (Image 5). Paper wasps fly with their legs hanging down, while yellow jackets tuck their legs against their bodies during flight.
Two common paper wasps species in Eastern Washington include the golden paper wasp (Polistes aurifer), which is native, and the European paper wasp (Polistes dominula), which was introduced into the U.S. in 1981 and reached the Pacific Northwest by 1999.
Similar to yellow jackets, paper wasps are beneficial predators that also feed on nectar. They do not scavenge non-living food as yellow jackets do though. They make paper nests, but their nests are built so that the comb cells are open to view from below (Image 6). These nests are often found in protected sites such as under eaves, and typically contain 20 or fewer cells.
The bald-faced hornet (Dolichovespula maculate) is another common wasp species that occurs in Eastern Washington. The bald-faced hornet in not really a hornet; hornets are in the genus Vespa and none actually occur in Washington. Bald-faced hornets are about three-quarters of an inch long and black and white/pale yellow (Image 7A).
Bald-faced hornets build a large papery nest that may have leaves and twigs on the outer nest wall (Image 7B). They are considered beneficial, as they feed almost entirely on living insects, including yellow jackets.
The wasp lifecycle
In the winter, mated wasp queens overwinter in protected areas, such as under bark or on the ground in weedy areas. The paper wasp may overwinter in attics or other parts of buildings, and can become stinging pests when temperatures inside the house increase.
Wasp queens will emerge in the spring, beginning to feed on nectar and build new nests. (Old nests are not reused.) Yellow jackets and bald-faced hornets work as individual queens to construct their own nests. European paper wasps sometimes work together as cooperating queens to make a shared nest.
A single egg is deposited in each cell. The queen cares for her larvae by feeding them chewed-up insects. The larvae emerge as adult worker wasps about one month after eggs are laid. The workers are infertile females; males are not produced until September.
As summer progresses, the workers that are produced maintain the nest, forage for food, and tend to the larvae; the queen just lays eggs. Bald-faced hornets and some species of yellow jacket may have nests consisting of hundreds to thousands of workers by late August or early September. Paper wasp nests are substantially smaller, seldom exceeding 100 individuals and often comprising fewer than 20.
In the fall, new reproductive males and queens are produced. These reproductives leave the nest and mate. The old queen dies, and the colony begins to die out thereafter. All workers and males die with the first freezing temperatures.
Back to last summer …
So what happened this past season? Why were there so many wasps? To start with, neither the Washington State Department of Natural Resources, nor the U.S. Forest Service (nor anyone else for that matter), release Vespidae wasps to control bark beetles or any other insect. Although wasps are beneficial predators, they are generalists and would not even begin to put a dent in the bark beetle population. On top of that, because bark beetles spend most of their lives under tree bark, they are largely inaccessible to Vespidae wasps.
There are many species of parasitoid wasps that are insect predators, some of which are specific to bark beetles. These wasps use their ovipositors as they were originally intended — to deposit eggs. Some parasitoids have very long ovipositors that allow them to deposit eggs under tree bark and into bark beetle tunnels. These eggs hatch into larvae that feed on bark beetle eggs, larvae, and sometimes adults.
Some species of parasitoid wasp deposit eggs inside insect larvae and feed on the larvae from the inside out. Others deposit eggs inside eggs, and the larvae feed on the eggs from the inside out. If you’ve ever wondered where people come up with alien scenarios in horror movies, you can look to parasitoid wasps!
Parasitoid wasps have been released for control of mostly invasive, nonnative insect species. One of the reasons nonnative species have the ability to become invasive is because they do not have natural enemies in their new habitat.
If eradication of an invasive species does not work and other controls measures are not working, sometimes entomologists will look for native enemies (often parasitoids) of these invasive species in their home habitats. These natural enemies are collected and studied in quarantine labs. If, after many rigorous tests, they are found to be safe to release in the U.S., they may be released as biological control agents. A good example would be the release of Agathis pumila (Image 8) for control of the larch casebearer (Coleophora laricella).
Biological control agents are rarely released for control of native species because native species typically have a suite of natural enemies with which they have evolved.
So if DNR and U.S. Forest Service didn’t release the wasps, why were there so many? Insect populations in general are largely controlled by the weather, and wasps are no exception. Spring weather in particular largely determines if we will have wasp problems. Mild springs allow overwintering queens to survive, whereas cold, rainy weather may reduce the likelihood that queens can build a nest and collect enough food to feed her offspring.
Summer weather can also contribute to wasp issues because warm summer weather accelerates wasp metabolism and growth rates, resulting in more wasps at a faster rate.
Wasps become most troublesome in late summer and early fall as colonies reach their maximum size. Yellow jackets are more readily provoked into stinging during this time, as natural foods become scarce and workers aggressively scavenge food scraps. Additionally, workers are more likely to vigorously defend their nests as new reproductive queens and males are produced.
For general protection around the house, you may want to keep lids on trashcans, clean up fallen fruit, and avoid wearing perfume. You don’t want to leave soda cans and food laying around. Wearing white or tan clothes can be helpful, whereas mosquito and tick repellents are not, as they don’t work against wasps.
If you do happen upon a ground nest, run away!
Keep running until the wasps stop their pursuit. Yellow jackets may chase you several feet. Wasps can sting you approximately four or five times before they run out of venom (unlike honey bees which can only sting you once).
If any land on you, flick them off. Do not swat or crush their bodies, as this will prompt them to release alarm pheromones that then stimulates a mass attack from other workers.
Although yellow jackets traps do work to trap yellow jackets (they do not attract paper wasps or bald-faced hornets), remember that there is no way you will control the yellow jacket population using them. Workers may be flying from as far as 4,000 feet away, and there may be many nests with hundreds of wasps in the surrounding area.
Traps are mainly useful for drawing yellow jackets away from areas where people congregate. Therefore, if you do invest in one, hang it away from these areas.
Homemade traps can work rather well, too. One such trap consists of a container (such as an old dishwasher tub) filled with water and dish detergent and a board laid over top with a piece of meat hanging beneath the board. Yellow jackets will remove a piece of meat and try to fly away with it, but the meat will make them heavier than normal, causing them to fall into the water. The detergent will act as a wetting agent, trapping the yellow jacket and making it unable to fly, leading to its death via drowning.
I made one myself last year using fish skin for my bait. At first, I thought the trap didn’t work at all, as I was coming home from work and hardly any yellow jackets were in it. But I quickly realized that one of my banty roosters was using it as his personal snack bar (Image 9).
Thereafter, I used vegetable oil instead of dish detergent as the wetting agent. I figured dish detergent may not be good for him. The vegetable oil seemed to work just as well.
If you need to destroy a nest, hiring a professional would be my first suggestion. If you choose to do it yourself, be sure to read the label of any insecticide you decide to use prior to treatment. Many are pyrethroids, nerve poisons that can be hazardous to humans, pets, and wildlife.
If you need to eradicate aerial nests, aerosol jet sprays and foam sprays are available. Dry dust insecticides would be best for German yellow jackets located in wall voids. For ground nests, use a liquid drench. Never use gasoline, as this will contaminate the soil and could contaminate ground water.
If you would prefer not to use insecticides in the soil, flooding a ground nest with water rarely works, but vacuuming can be effective (and should only done by a professional).
Treat nests after dark when flight activity is minimal. Do not shine a flash light directly at the nest. Spray the insecticide into the nest entrance first, then spray the nest surface, then soak the entire nest. Leave it for a day or two before removing, as any workers that were not in the nest may come back and come into contact with the insecticide.
Given the fact that wasps are ecologically beneficial, I would only use control if they are a direct threat. Pay attention to what species you are considering eradicating. While yellow jackets are indeed a rather aggressive species, bald-faced hornets are less so and paper wasps are actually quite docile (although both will sting to defend their nests).
Let’s all hope next season is less exciting in the world of wasps!
Akre, R.D. and Antonelli, A.L. 2003. Yellowjackets and Paper wasps. Revised by Peter Landolt and Arthur L. Antonelli. Washington State University Cooperative Extension, EB0643. 7p.
Bechinski, E., Merickel, F., Stoltman, L. and Homan, H. 2009. Homeowner guide to Yellowjackets, Bald-faced Hornets, and Paper wasps. University of Idaho Extension, BUL 852. 16p.
Buck, M., Marshall, S.A. and Cheung D.K.B. 2008. Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region. Canadian Journal of Arthropod Identification No. 5: 492 pp. Available online at doi: 10.3752/cjai.2008.05
Bush, M.R. and Murray, T.A. 2014. The European Paper Wasp. Washington State University Extension Fact Sheet, FS152E. 5p.