Common Name: Yellow jacket, Yellow wasp – The predominant yellow bands are only on the dorsal side of the thorax, metaphorically a yellow jacket. They are simply called ‘wasps’ in every other English speaking country.
Scientific Name: Vespula spp – The Latin word for wasp is vespa; the generic name is then “little wasp.” Spp is the plural of species and implies variety. The depicted species is the southern yellow jacket (V. squamosa).
Potpourri: An attack by yellow-jacket wasps can transmogrify a woodsy walk into a Gadarene stampede in seconds. Using the three dimensional space of airborne assault, they come from everywhere and nowhere like ring wraiths all at once; the only option is to outrun them in one of the two dimensions available. Their demonic rage comes unbidden, absent any overt act of aggression by its victims, who righteously feel that they have been ambushed for no reason. But it is the law of the jungle that reigns supreme in nature’s domain; fear motivates yellow-jacket wasp aggression. They rarely if ever attack one or two hikers who travel quietly and placidly, but larger groups who fill the woods with noise and vibration are at risk. Their nest is their home and must be guarded at all costs. It contains the queen and all of her many children that are the genetic heritage of the flying tigers who launch sortie after sortie to drive off the perceived threat. Large mammals, notably bears and racoons, are the greatest dangers to the insect broods; larvae are one of their primary protein sources. To a wasp, a hiker is just another threatening animal and a large group makes it worse. Their action is natural, perfectly justifiable in achieving the desired result of meeting the threat sting-on. When traipsing through the territory of wild things, it is necessary to be understanding and humble. If you get stung, it will hurt for a while and may turn red, but if the wasp fails to protect the next generation, it is existential. Stinging insects may be anathema to the sheltered, pain-free life of modern humans but they are a vital link in forest faunal ecology. They deserve respect and even admiration for their selfless colony-protecting ferocity.
Wasp is the collective name given to any member of the Order Hymenoptera that is not an ant, a bee or a sawfly. They are noted for the very narrow appendage between the thorax and the abdomen; ants have a similar “wasp waist” since they evolved from wasps. The hymenopterans comprise one of the largest assemblages of living things on earth, contending with the flies (Diptera) and beetles (Coleoptera) for that distinction. While many have the membranous wings for which they are named, hymen means membrane in Greek, they are not uniquely thus endowed; flies also fly with them. The front and rear wings of bees and wasps are joined by little hooks called hamuli so that they operate in synchrony; married wings is another possible Hymenoptera interpretation. Hymen was the Roman god of marriage who was mythologically born of Apollo and one of the muses; metaphorically hymen is the name of the membrane at the threshold of marriage consummation. Notably the hymenopterans comprise the bulk of the insects living in large complex societies known as eusocial, marriage as production of progeny taken to the extreme. Globally, there are about 15,000 species of wasps of which 4,000 are indigenous to North America. Many species use the sting as a means of paralyzing their mostly arthropod prey to immobilize them in order to lay eggs; the hatchling larvae offered a ready meal of protein. These wasps are called parasitoid, an intermediate between a parasite which does not kill its host and a predator which kills multiple species. Parasitoid behaviors in different families of wasps vary according to environmental factors, the driving force to Darwin’s “endless forms most beautiful and wonderful.” To the wasps perhaps; not so much to their prey.
Parasitoid wasp propagation strategy depends on the immobilization of protein-rich insects, mostly caterpillars, as a food source for their larvae. In denser habitats rife with competition for scant resources by millions of carnivores, workaround adaptations became necessary, as other hungry predators ate both the inert insect and the parasitoid wasp larvae for which it was intended. Evolutionary adaptation resulted in two divergent behaviors: do away with immobilization altogether and allow the host to protect and feed itself on a temporary basis; or carry the stunned insect carcass to a protected lair to be consumed at leisure. The former is the province of the Ichneumon wasp family whose diversity attests to the success of the non-kill adaptation; there are 3,300 species in North America and twenty times that many globally, each targeting a single or small group of insect host species.  Nature’s invidious solution to the purloining problem was the slow death of being eaten alive from the inside out. Absent the sting of immobilization, the hapless host becomes a mobile meal cart for the larvae that instinctively burrow seeking sustenance after hatching from the eggs laid by the wasps. With mindless yet cunning cruelty, the larvae consume the vital organs last to prolong the meal in a drawn out death by a thousand cuts. The evil implicit in this act troubled Darwin, who wrote “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention with their feeding within the living bodies of caterpillars.”  There are even wasps that attack spiders, reversing roles with the master predator arachnids. The wasp larvae hijack the spider’s web-making skills to build a support for their cocoons which they occupy after having finished off the remains of the spider; it is not yet clear exactly how they do this.  What is certain is that the victimized host feels pain as it is being consumed; pain is necessary for any animal to be aware of a survival threat and the necessity to take remedial action. In the ‘ignorance is bliss’ worldview, only humans feel pain and dumb animals don’t; the height of hypocrisy.
Killing or paralyzing insect prey and bringing them to a nest is the province of the larger wasps including yellow jackets and hornets. Yellow jackets are in the Hymenopteran suborder Aculeata, which is derived from the Latin aculeus meaning ‘sting,’ their most notable trait. The suborder is defined according to the evolutionary mutation of the egg-laying ovipositor organ into an efficient venom delivery device. The aculeate wasps that live in colony groupings are taxonomically assigned to the sub-family Vespinae and may be called either yellow jacket (genus Vespula) if they have the characteristic black and yellow markings or hornet (genus Vespa), their larger, darker cousins – mostly black with some yellowish markings on the head and thorax. Aculeate yellow jacket wasps are further divided into two groups: the benign V. rufa live in small colonies and use the sting only as an offensive weapon to paralyze prey; the pestiferous V. vulgaris live in large colonies and use the sting as a means of colony defense.  The colony arrangement is known as eusocial, a relatively modern biological term that refers to arthropods (bees, ants, termites and some yellow jacket wasps) that live in large, complex societies in which a division of labor prevails according to differences in size, sex and sometimes shape. According to the noted biologist Edward Wilson, eusocial insects evolved because of their nest building behaviors – “in all of the animal species that have attained eusociality, altruistic cooperation protects a persistent, defensible nest from enemies.”  This conflicts with the traditional alternative view that the eusocial division of labor arose independently and the nest became a necessary adjunct for colony growth and maintenance. In either case, the palladium of the nest is the essence of the colony. As a result, the nest is defended with farouche ferocity whenever a threat is perceived; yellow jackets emerge en masse to strike at any unwary interloper, hikers included, with multiple defensive stings.
The queen is the cynosure of Hymenopteran colonial society; there is no king. Eusocial societies are structurally matriarchal; the only function of the male is to provide some DNA diversity to promote evolutionary adaptability. The survival of the yellow jacket species depends on the success of the queen in finding a safe haven to survive the winter months and equally on her ability to start a colony with vernal warming. The queen’s Herculean labors begin with the construction of a hypogeal or underground nest (epigeal in some species) made from plant fibers that are assiduously removed from decayed wood and assembled into about thirty cells for egg deposition; a paper-like shroud made from masticated cellulose provides a protective covering. The vespine larvae that emerge from each egg must each be fed for several weeks until they pupate to metamorphose into adult female workers. The queen is the sole provider and protector of the colony for the first and most critical month of its existence; she must compete with myriad other arthropods for flower nectar to nourish her larval offspring and catch and malaxate insect prey to provide the proteins needed for growth. The unrelenting duties of larval care persist until midsummer, when the emergent female workers take over the mundane chores and relieve the queen to focus on her sui generis oviposition function. A period of Malthusian growth ensues as the workers build more cells for more workers in the expanding, multi-layered nest – eusocial haven. Ultimately, between 500 and 4,000 female workers will have constructed between 2,500 and 10,000 cells, the differences in size and population a matter of the serendipitous choice of a good location with adequate food resources. As summer wanes to the senescence of autumn, cells are constructed for the growth of new queens and a small number of necessary (but sufficient) males; the next generation queens and their attendant males depart the nest with the single-mindedness of procreation for species propagation. The males almost immediately die as the mission of consummation is completed by the lucky few; the new, fertilized queens carry their future offspring to carry the cycle of life through winter to the following spring. The female workers and the original queen are left behind to succumb to their inexorable fate of colony collapse, the paper shell nest a testimonial relic to their passage. 
There are two species of yellow jacket that warrant special consideration: the southern yellow jacket (V. squamosa) indigenous to southeastern North America, and the European yellow jacket (V. germanica) indigenous to Eurasia but globally invasive and notably aggressive. Both species are considered significant pests, particularly in warmer climates where their nests can become perennial rather than dying out at the annual onset winter and can therefore expand to gargantuan size and population. A nest of southern yellow jackets was found in Florida with 14 comb levels and 120,130 cells (presumably enumerated by meticulous count); however the record goes to a nest of invasive European yellow jackets found in New Zealand that was 15 feet tall, had about 180 combs with an estimated population in the tens of thousands. The larger nests become unkempt with carcasses of dead prey and dead workers accumulating at the margins; southern yellow jackets even allow cockroaches to roam their nests as scavengers in one of the more interesting examples of mutualism. Southern yellow jackets are particularly insidious, as the queens will preferentially invade the nest of another, less aggressive yellow jacket species (mostly V. maculifrons) rather than following the traditional and more onerous task of cell by cell nest construction; 80 percent of all V. squamosa nests inspected in a field study were usurped from other species. This behavioral pattern is called facultative parasitism and marks the incidence of evolutionary deviation away from the one queen/nest colony to a polygynous (multi-queen) social order. The multiple queen model of V. squamosa extends to the larger, perennial nests pervasive in warmer climates, the increased volume allowing for independent sub-colonies under individual regencies. The net result is more yellow jackets defending larger nests that need more food to feed both themselves and the larvae they maintain – and the incipience of a pest management problem. 
In smaller, annual colonies, the consumption of dead insects, nectar, and fruit sugars
suffices to meet alimentary needs of its denizen wasps. Another important part of their omnivore diet is the consumption of what may euphemistically be called the ‘digestive excretions’ of the larvae they tend. While execrable to humans, trophallaxis (Greek for food exchange) is quite common among arthropods; many ant species “herd” aphids to collect their excrement which is known as honeydew – because it collects on leaves in small, sweet droplets; more generally, insect excrement is called frass.  The pernicious predation of yellow jackets on other insects has resulted in some evolutionary pressure for tree boring beetles to employ mimicry in the form of yellow jacket markings on the wing-covering elytra. In larger colonies, the demand outstrips the supply, and hungry yellow jackets seek out new sources of food, the most available sources of which are anthropomorphic and include the standard picnic fare of carbonated drinks, cakes, fruit, and ice cream. Many a bucolic picnic has ended in panic. The insatiable appetite of the yellow jacket hordes is not confined to humans. A yellow jacket foray was reported at Portland, Oregon Zoological Garden in 1973 that was so pervasive that it even drove the lions from their food; tigers on the Indian subcontinent have been observed blowing on the carcass of their downed prey to rid it of wasps prior to feeding – probably from painful experience. Yellow jackets are also known to attack honeybee hives for nutrition, a problem for apiarists, to say nothing of the bees themselves. The economic losses due to yellow jacket depredations are difficult to estimate but are thought to be substantial. Stings to various agricultural workers in California resulted in an estimated loss of $200,000 in 1968 due to lost hours and productivity. In one 5 year period, 5 percent of all Forest Service medical expenses (lost time and treatment) were due to wasp stings. In 1975, over 90 percent of all of the (mostly pinot noir) grapes in Oregon and Washington were ruined by yellow jackets piecing the grape skin to feed on the juice. 
According to the Centers for Disease Control, stings from wasps, bees and hornets are theleading cause of human mortality in the United States due to animal interaction among all categories (90 -100 deaths per year). Admittedly, this is partly due to an allergic life-threatening reaction to bee and wasp venom called anaphylactic shock; it is estimated that about 0.5% of the population is susceptible.  By comparison deaths due to sharks and alligators are negligible (1 per year each). The closest competitor category is “other mammals,” at 52 per year.  This is consistent with previous work: a study of the period 1950-1959 found that 229 of 460 recorded deaths due to venomous animals were Hymenopterans. This should come as no surprise since yellow jackets can sting multiple times and frequently attack in large groups. Wasp stinger physiology differs from that of the bees; bee stingers are barbed to prevent retraction and bees can therefore only sting once (after which they die due to evisceration). Yellow jacket stingers are smooth and can be extracted and reinserted multiple times. Another factor is that the yellow jacket sting is a defensive weapon; their venom is accordingly much more potent than that of the other aculeate wasps, whose sting is mild by comparison. A complicated mixture of biologically active agents including histamine, serotonin and noradrenalin, the venom causes muscle contraction, vasodilation of blood vessels (lowering blood pressure), tissue destruction and intense pain.  Yellow jackets attack in swarms because their venom also contains pheromones that incite alarm; the act of stinging automatically instigates a synchronized attack by all yellow jackets within olfactory range. In a 1987 study, which was inspired by the observation that yellow jackets being removed with a vacuum cleaner stung the sides of the extraction hose, extracts of yellow jacket venom were found to induce “recruitment from the nest, flight to the source, and stinging attacks.” 
So what’s a hiker to do? Run like hell; yellow jackets brook no defense. The virulence of the venom and the enticements of its pheromones are evolutionary adaptations to defend the nest against large mammals that must be driven off with collective power to protect the colony. The innocent hiker is just another large mammal that must be held at bay. Yellow jackets do not stray too far from the nest during defense; it remains the cynosure of their every instinct. After ten meters or so, they will rarely if ever pursue; the run is a sprint and not a marathon. Having safely extricated from the combat zone, it is best to stop and take stock of the missing and wounded. Conventional treatment is to remove the stinger, clean the area, take Benadryl (diphenhydramine) to reduce swelling and any of the various pain medications as needed.  Since yellow jackets don’t leave their stinger, that part is easy. Complications can arise with numerous stings as the effects are cumulative; any hiker who is allergic to bee or wasp stings should carry epinephrine and be ready to use it. For a single sting, do nothing and you will feel fine in less than an hour. Leibnitz’s theodicy would allow that some suffering is necessary for the greater good, which is nature’s delicate balance of all living things in the intricacy of ecology. Were it not for the wasps that sting, the world could well be overtaken by the plant eating caterpillars that would then be unchecked. Were it not for the wasps and bees that collect nectar, many plants would go unpollinated and simply vanish. There are 8 million animal and plant species on earth of which 5.5 million are insects. They are all important as they are the web of nature. It was recently estimated that 1 million would become extinct within decades.  If a wasp nest survives by exercising its stinging defensive strategy, it is a small price to pay for the greater good.
1. Marshall, S. Insects, Their Natural History and Diversity, Firefly Books, Ontario, Canada, 2006. pp 518-521, 532-533.
2. Haskell, D, The Forest Unseen, A Year’s Watch in Nature, Penguin Books, New York, 2013, pp 143-145.
3. Eberhard, W., Gonzaga, M. “Evidence that Polysphincta-group wasps (Hymenoptera: Ichneumonidae) use ecdysteriods to manipulate web-construction behavior of their spider hosts” Biological Journal of the Linnean Society News release of the Smithsonian Tropical Research Institute, 29 April 2019.
4. Marshall, S. Op. cit.
5. Wilson, E. The Social Conquest of Earth Liveright Publishing, New York, pp. 139-147.
6. Akre, R., et al, Yellowjackets of North America, North of Mexico, U. S. Department of Agriculture, Washington, D. C. Handbook number 552, 1980.
8. Milne, L. and Milne, M. National Audubon Society Field Guide to North American Insects and Spiders, Alfred A. Knopf, New York, 1980, p 821.
9. Akre, R. Op. cit.
11. Ingraham, C. Chart: “The animals that are most likely to kill you this summer” Washington Post June 16, 2015.
12. Akre, R. Op. cit.
13. Landolt, P. and Heath, R. “Alarm Pheromone Behavior of Vespula squamosa (Hymenoptera: Vespidae) Florida Entomologist Number 70 June 1987.
14. American Red Cross First Aid/CPR/AED Participants Manual p.88. available at https://www.redcross.org/content/dam/redcross/atg/PDFs/Take_a_Class/FA_CPR_AED_PM_sample_chapter.pdf
15. Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services Media Release: Nature’s Dangerous Decline ‘Unprecedented’; Species Extinction Rates ‘Accelerating’ 6 May 2019 at https://www.ipbes.net/news/Media-Release-Global-Assessment