INTRODUCTION — The stinging Hymenoptera are taxonomically divided into three principal groups: ants, bees, and wasps. The majority of allergic reactions to stings are due to this order of insects. This topic reviews the biology and identification of the flying Hymenoptera that include bees, yellow jackets, hornets, and wasps. Avoidance of the flying Hymenoptera is discussed separately, as are fire ants, which are also members of the Hymenoptera order. (See "Stinging insects: Avoidance" and "Entomology and control of imported fire ants".)
Diagnosis and management of stinging insect allergy is discussed separately. (See "Bee, yellow jacket, wasp, and other Hymenoptera stings: Reaction types and acute management" and "Diagnosis of Hymenoptera venom allergy" and "Hymenoptera venom immunotherapy: Efficacy, indications, and mechanism of action" and "Stings of imported fire ants: Clinical manifestations, diagnosis, and treatment".)
OVERVIEW — Numerous misconceptions about Hymenoptera taxonomy, biology, stinging behavior, and sting avoidance are widespread throughout the clinical literature [1]. This is due partly to the repeated citation of references written by nonentomologists containing fundamental errors and partly to the extensive use of common names for these insects, such as "bee," "wasp," and "hornet." These informal expressions are often used imprecisely by clinicians as well as the general public. However, biologists have long adhered to a set of specific meanings for the most frequently used insect common names, as well as a standardized peer review process to create new ones [2,3]. These familiar terms, when used correctly, can facilitate communication between clinicians and their patients.
This topic review will adhere to the well-established entomologic convention that calls the aculeus (ie, a modified ovipositor used as a venom-injection device) a "sting," although the colloquial term is "stinger" [4-6]. No male Hymenoptera can sting because the aculeus is a female organ.
The stinging Hymenoptera are taxonomically divided into three principal groups: ants, bees, and wasps. Only bees and wasps will be discussed here.
The most important aspects of bee and wasp biology, from a clinical standpoint, involve two principal dichotomies:
●The first major distinction is that of eusocial (highly social) versus solitary or primitively social species. Most bees and wasps are solitary, meaning that a single female builds a nest without assistance to rear her brood of new males and females. The purpose of her sting is for intraspecific competition over nest resources, self-defense against predators, and (in the case of solitary wasps) prey capture [6,7]. These insects will not sting to protect their nest and present no hazard to humans under most circumstances.
A relatively few bee and wasp species are eusocial. A female (termed a "queen") uses her sterile daughters (termed "workers") to build a nest and rear a colony of additional workers, which eventually rear a brood of new males and reproductive females. Worker bees and wasps will readily sting in defense of their nest if they perceive that it is threatened, unlike solitary or primitively social species. They will also sting in self-defense [5,8].
●The second dichotomy involves the two circumstances under which worker bees and wasps use their stings. Humans most often are stung because of accidental contact with an individual worker that is foraging for food, water, or building materials away from its nest. This lone worker delivers a single, reflexive sting in defense of its life. In contrast, disturbing a nest, or being in the vicinity of a disturbed nest, may lead to multiple stings from its alarmed workers, even if the nest itself is not directly contacted. These two sets of circumstances present completely different risk factors, requiring different types of avoidance measures [1].
BIOLOGY AND IDENTIFICATION — For simplicity, this topic review will refer to the eusocial bees and wasps that constitute the major stinging threat to humans as "social" and the remaining species as "solitary."
Social bees — All social bees are classified in the family, Apidae. In general, bees are distinguished from other Hymenoptera by their collection of pollen as the protein source for their larvae. Social bees also feed their larvae honey, which they manufacture from collected floral nectar. Their nests are made of wax, which the bees secrete from glands on their abdomen [7,8]. The term "hive" is properly used only for manmade containers that house domesticated bees.
Bumble bees — Bumble bees are robust, easily recognized bees with a dense coat of black and yellow (or occasionally orange and white) fur (picture 1 and table 1). There are 46 bumble bee species in North America north of Mexico, all of which are in the genus Bombus [9]. Colonies last only one season, are typically rather small (usually less than 50 workers), and often located in old rodent burrows or other cavities that are not prone to human disturbance [7,10].
Honey bees — Throughout much of the world, the name "honey bee" refers to a single species, Apis mellifera. This species evolved in tropical Africa and was widely bred by humans into numerous subspecies (picture 2 and table 1) [7,11]. Other than in its native region, all colonies living in natural circumstances are considered feral in that they have originated from domesticated lineages. Unlike bumble bees and most social wasps, honey bee colonies are able to survive temperate winters because of their stored honey and heat-producing clustering behavior [7,8]. Members of the genus Apis are well known for their "sting autotomy," in which the sting anchors in vertebrate flesh by means of harpoon-like barbs, is spontaneously torn from the abdomen by the bee's own escape efforts, and continues to inject venom into the victim [4,12,13]. The bee invariably dies from its wounds.
Honey bee colonies range from 40,000 to 80,000 workers. Accidental disturbance of feral colonies in the United States was rare until the 1990s because nests were typically located within tree cavities or structural voids [14,15]. The arrival of Africanized honey bees (hybrids of various domestic honey bees with the African subspecies Apis mellifera scutellata) in 1990 markedly increased the stinging risk for people and domestic animals over much of the South (figure 1) since these bees establish nests in a wide variety of locations that are readily subject to human disturbance [16-19]. In addition, this bee has an extremely low defensive response threshold and is capable of some of the most severe attacks known for any social insect. This hyperdefensive behavior has earned them the alarmist title of "killer bees" by the popular media. Africanized bees are indistinguishable in appearance and venom chemistry from typical "European" honey bees.
Solitary bees — Several families of bees, including Apidae, contain solitary species. Most are innocuous, although a few occasionally come to the attention of clinicians either because of unusual stinging incidents or patient concerns due to their appearance. Allergy to the venom of all of these types of bees is rare and is most commonly reported for sweat bees due to their greater proximity to humans [20].
Sweat bees — Sweat bees are tiny bees in the family Halictidae that are attracted to human perspiration (picture 3 and table 1). They often sting when accidentally pressed. These bees can be an annoying nuisance but are dangerous only to those who are allergic to their venom.
Carpenter bees — Carpenter bees (Apidae) are large bees that bore into structural wood and bear a superficial resemblance to bumble bees (picture 4 and table 1). The territorial males may aggressively hover close to people but are completely harmless.
Mining and digger bees — Mining and digger bees (Andrenidae and Apidae) may be abundant where soil conditions favor burrow construction. As with carpenter bees, most of the individuals flying back and forth in these aggregations are harmless males [7].
Social wasps — All social wasps are classified in the family Vespidae, which also includes some solitary forms. The two medically important subfamilies are the Vespinae (commonly known in the United States as yellow jackets and hornets) and the Polistinae (commonly referred to as paper wasps). Members of both subfamilies construct distinctive nests out of wood fibers scraped from either sound (eg, fence posts) or rotted (eg, decaying logs) sources and mixed with saliva to form a paper-like material. Unlike bees, the protein source for larval growth is live arthropod prey subdued with the mandibles (not the sting). Some pestiferous yellow jacket species scavenge carrion or human food. Colonies of social wasps normally last for only one season and die out in the fall and winter in temperate regions [21,22].
One of the more enduring myths in the clinical and popular literature is that wasp stings are "smooth," in contrast to the honey bee, enabling the insect to sting repeatedly. In fact, the stings of virtually all social wasps are barbed to some degree, and sting autotomy (see 'Honey bees' above) has been recorded for many more (mostly tropical) wasp species than for bees [23]. However, most species of wasps can withdraw and reinsert their sting.
Yellow jackets and hornets — These members of the subfamily Vespinae are the most common source of stings in temperate regions due to their abundance and colony aggressiveness [1,21]. There are 20 species of yellow jackets and hornets in the United States and Canada, although the group's taxonomy has seen frequent changes over time [24,25]. A few species have a unique appearance and can be readily identified (figure 1). The remaining species have similar patterns of bright yellow and black, and the patterns are often variable within a species. Thus, a specialist may be required to positively identify them.
●Genus Vespa – This genus comprises the true hornets, most of which are found in Eastern Asia. A single, introduced species is established in the United States: V. crabro, commonly called the European hornet (picture 5 and table 1). It is a large, brown and yellow wasp that typically nests in tree cavities, attics, or outbuildings. It is not a common source of stings, due to its relative scarcity, nonscavenging behavior, and high visibility (making surprise encounters unlikely) [21]. Since 2019, V. mandarinia, the Asian giant hornet, has been sporadically detected in the US in a limited, sparsely populated area of the Pacific Northwest [26]. Dubbed "murder hornets" by the popular media, the name refers both to its severe attacks on beehives and its potential as a dangerous stinging threat to humans if its colonies are disturbed. It is unclear whether this species has become firmly established, and, if so, how far it may spread in the future [27].
●Genus Dolichovespula – This genus of yellow jackets is distinguished by their familiar, gray aerial nests, constructed on buildings or in vegetation (picture 6 and picture 7 and table 1). They are often colloquially called "hornets" in the United States, probably because one common, atypically large species superficially resembles the European hornet [3]. This distinctive black and white wasp, D. maculata, even has the accepted common name of "bald-faced hornet" (sometimes incorrectly referred to as a "white-faced hornet") (picture 8) [2]. A second abundant species, D. arenaria, is the size and color of most other yellow jackets and has the common name of aerial yellow jacket [2]. It is also referred to as the "yellow hornet," a confusing misnomer that should be discontinued [2,28].
●Genus Vespula – This genus of yellow jackets builds nests in cavities, either subterranean or in protected structural locations, such as wall voids and attics (picture 9 and table 1). One group of six species is particularly important in the United States and Canada due to their large colony size (potentially approximately 5000 living workers at colony maturity), long colony life (sometimes persisting into early winter), and propensity for scavenging a wide range of human foods. These species are V. alascensis (formerly misidentified as the Old World V. vulgaris [29], common yellow jacket), V. maculifrons (Eastern yellow jacket), V. pensylvanica (Western yellow jacket), V. squamosa (Southern yellow jacket), V. germanica (German yellow jacket), and V. flavopilosa (picture 10 and picture 11). Colonies of these species typically have a single queen and last for one season only, as with all temperate social wasps. However, in areas with mild winters, including the Southeastern states, California, and Hawaii, multiple queens may coexist in the same nest and produce enormous perennial colonies with a high potential for mass stinging [1,30].
Clinical studies and field observations have shown that both the Eastern yellow jacket and V. flavopilosa often anchor their stings firmly in human skin (picture 12) [23,31-33]. The wasps cannot pull away from (ie, autotomize) their sting (see 'Honey bees' above). However, the embedded sting apparatus is readily torn from the wasp's abdomen if the insect is forcibly removed by the victim. This mechanism of sting loss by traumatic evisceration is functionally similar to the true autotomy of honey bees since it is associated with the release of alarm pheromone and prolonged injection of venom [23,31-33].
Paper wasps — Paper wasps (members of the subfamily Polistinae) are another common source of human stings in temperate areas. There are 24 species of paper wasps in the United States and Canada. Identification of these species is particularly difficult for the nonspecialist [25,34]. Paper wasps are more slender and elongated than yellow jackets (figure 2). They construct distinctive nests of only one comb without any protective covering (picture 13 and table 1). The colonies are typically small, with no more than a few dozen workers. However, their nests can be abundant around human habitations. P. dominula (often incorrectly cited as dominulus) is especially pestiferous since it nests in both exposed and protected locations, including readily disturbed structural cavities, such as hollow fencing, light fixtures, and playground equipment [25,35-37]. Many paper wasp species are extensively colored in shades of brown, varying from dark to reddish, and, when they have yellow markings, these are usually pale. In contrast, P. dominula has an atypically bright yellow and black pattern and has a relatively small size and compact shape, which frequently results in it being misidentified as a yellow jacket (picture 14).
Solitary wasps — Several families of wasps, including Vespidae, contain solitary species. Most are innocuous, although, as with bees, a few occasionally come to the attention of clinicians either because of unusual stinging incidents or patient concerns due to their appearance. Allergy to the venom of these wasps is rare.
Cicada killers — Cicada killers (Sphecius spp, Crabronidae, formerly treated as part of Sphecidae) are enormous wasps that prey on annual cicadas. They nest in the ground, often excavating conspicuous mounds of earth in the process. Numerous females will sometimes dig their burrows in the same vicinity, resulting in large numbers of males (picture 15 and table 1) flying back and forth in the area.
Mud daubers — Mud daubers (Crabronidae and Sphecidae) frequently build their earthen nests in protected areas on structures (picture 16).
Velvet ants — Velvet "ants" are the wingless, ant-like females of wasp species in the family Mutillidae [6,38]. They are typically covered in bright red and black hair. Their aculeus is exceptionally long and maneuverable, and envenomation by these wasps is extremely painful, hence their common name of "cow killers" in some parts of the United States.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Stinging insect allergy".)
SUMMARY AND RECOMMENDATIONS
●The great majority of bee and wasp species are solitary or primitively social and will not use their stings to defend their nests. They therefore will not sting unless accidentally pressed against the skin. Allergy to the venom of these bee and wasp species is rare. Included in this group are such familiar forms as carpenter bees, mining (or digger) bees, cicada killer wasps, and mud dauber wasps. (See 'Solitary bees' above and 'Solitary wasps' above.)
●In temperate areas, almost all stings from bees and wasps are from three highly social groups that will sting to defend their nests: honey bees, vespine wasps (yellow jackets and hornets), and polistine wasps (paper wasps). (See 'Social bees' above and 'Social wasps' above.)
●Africanized honey bees are now found throughout much of the Southern United States. This insect constitutes the most dangerous stinging threat to humans in areas where it occurs due to the extreme sensitivity of their colonies to disturbance and their typically massive and prolonged attacks. (See 'Honey bees' above.)
