Stinging insects: Avoidance

INTRODUCTION — This topic reviews how to avoid being stung by the types of Hymenoptera with flying workers (ie, social bees [including honey and bumble bees] and social wasps [including yellowjackets, hornets, and paper wasps]).

Stinging ants are discussed in detail separately. (See "Stings of imported fire ants: Clinical manifestations, diagnosis, and treatment", section on 'Fire ant avoidance'.)

The biology and identification of the flying Hymenoptera, as well as fire ants, which are also members of the Hymenoptera order, are discussed separately. (See "Stinging insects: Biology and identification" and "Entomology and control of imported fire ants".)

Diagnosis and management of stinging insect allergy are 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 — The Hymenoptera is one of the largest insect orders, consisting of more than 150,000 species of wasps, bees, and ants, the vast majority of which are harmless to humans (figure 1). The females of one subgroup called the Aculeata have their ovipositor modified into a sting apparatus (vernacular, "stinger") capable of injecting venom that may produce an allergic reaction. Almost all cases of human stings are from social species that live in colonies consisting of three physiologic castes: one or more fertile queens, responsible for reproduction; a large number of usually sterile female workers that construct, maintain, and defend the nest, as well as feed the immatures; and a smaller number of males (which cannot sting since they lack the modified ovipositor and, in honey bees, are called drones). It is the workers that are responsible for the majority of human stings.

SCENARIOS THAT PROVOKE ATTACKS — The most important concept of sting prevention is recognizing that there are two completely different scenarios in which worker bees or wasps are provoked to attack:

●The first involves single workers away from their nest, which typically are harmless unless directly touched.

●The second involves disturbing the nest of a colony, which typically results in defensive behavior of multiple workers, including stinging, even if the nest itself is not directly touched.

AVOIDANCE OF STINGS FROM INDIVIDUAL WORKERS

Actions that promote stings and misconceptions — The public often mistakenly thinks of bees and wasps as inherently aggressive under any circumstances due to the ease with which some colonies are stimulated to attack in defense of their nest. In reality, individual workers away from the nest tend to narrowly focus on foraging and typically ignore humans, even when close to them. Stings are almost always provoked by firm, accidental contact, such as stepping on a worker, taking the insect into the mouth with food or drink, or pressing/striking a bee or wasp with the hand. The risk of being stung is therefore elevated in locations where large numbers of bees or wasps have congregated to feed, particularly where humans are doing the same [1-4].

Personal behavior — The most appropriate advice may be simply to not eat or drink outdoors during the warm months, depending upon the extent of a patient's concern [5]. Less extreme preventive measures in locations, such as picnic areas and concession stands, involve minimizing accidental contact with foragers and include [4,6]:

●Maintaining a high level of vigilance as to the presence of bees and wasps in the immediate vicinity

●Not walking with exposed feet

●Being careful when drinking beverages

Drinking directly out of cans or bottles presents the greatest risk since these containers are readily entered by inquisitive foragers that are subsequently concealed from view. Tightly lidded cups with inserted straws are often recommended as safer than open cups but do not totally exclude entry by the smaller species. Open cups or glasses that afford an unobstructed view of the liquid are probably the safest option.

Repellents — There are no effective repellent products for foraging bees or wasps, despite advertising claims to the contrary.

Wardrobe and cosmetic fragrance — There is no empiric evidence that cosmetic fragrances/perfume or bright, floral-colored clothing significantly increases a person's attractiveness to individual foraging Hymenoptera or the risk of getting stung by them. However, attacking insects from a colony are strongly attracted to dark colors, and wearing white or light colors may help in such a situation. (See 'Mitigating the severity of attacks' below.)

Both honey bees and certain vespine species collect carbohydrates from a wide array of natural and manmade sources besides floral nectar, particularly fermenting fruit and sweet beverages and foods [7,8]. Orientation to these resources involves olfactory recognition of distinctive volatile cues [8-10]. Nevertheless, there are no published data demonstrating a significant attractive effect of any cosmetic product for any Hymenoptera species. To the contrary, the principal components of lavender, a floral scent widely used in perfumes and cosmetics, have been experimentally shown to reduce the aggressive response triggered by honey bee alarm pheromone, thereby exerting a calming effect on disturbed honey bees [11]. Despite this, public information distributed by the medical community often contains advice concerning wardrobe and cosmetic selection to minimize the chances of being stung. For example, "Many stinging insects are foraging for food, so do not look or smell like a flower. Avoid brightly colored clothing and perfume when outdoors" [12].

The effect of fragrances can be unpredictable, as potentially occurs with the alarm pheromone produced by the northern giant hornet, Vespa mandarinia. Alarm pheromones are chemical compounds that are released by bees or wasps to attract other colony members to the location to aid in defense. The northern giant hornet has an alarm pheromone that incorporates alcohols and esters that are also used in food flavorings and cosmetic fragrances [13]. However, it is unknown whether or not any specific product incorporating these chemicals elicits defensive behavior by this species.

Orientation to flowers by bees is governed by a complex suite of integrated factors such as floral colors (including both ultraviolet and infrared hues invisible to humans), patterns, and shapes; specific floral odors supplemented by multiple olfactory cues provided by the local environment; floral temperature; and the recent foraging history of individual workers [14-17]. A preconception of what a target item looks like and where it is found, termed the "search image," is derived from the aggregate of specific stimuli used by an organism to detect its food. Unlike humans, bees are most sensitive to the short-wavelength end of the spectrum, particularly ultraviolet light, followed by blue-violet and green. They are least sensitive to orange and cannot perceive red [15,16]. As a result, flowers that depend upon bees for pollination typically have evolved distinctive ultraviolet patterns that are highly visible to the insects but are often not perceived by humans [16,18]. The search image of foraging bees is therefore unlikely to be triggered by a large patch of colored cloth that appears bright to humans but has limited or no biologic significance to Hymenoptera [5].

Forager reduction — Another approach to avoiding stings associated with foraging bees and wasps involves implementing measures to reduce the number of foragers.

One method is to minimize local sources of attraction [1,4,6]:

●Tightly cover food and waste receptacles.

●Frequently clean surfaces of food residue.

●Frequently remove refuse, fallen fruit, and dog or other animal feces (since the attendant flies are hunted by some wasp species).

●Eliminate landscape plantings that attract large numbers of carbohydrate-seeking Hymenoptera. This measure is generally justified only in extreme circumstances and typically requires consultation with a local landscape specialist to obtain plant names appropriate for the locality. In many cases, Hymenoptera are not attracted to the flowers or fruit on these plants but to "honeydew," the sugar-rich excrement of sap-sucking insects, such as aphids, mealybugs, and scales.

A more direct tactic is to attempt to reduce forager populations with the use of baits, either by luring the insects into traps or as a means to deliver a pesticide:

●Numerous models of wasp traps are on the market [19,20]. However, they tend to be swamped by the constantly replenishing colonies within foraging range unless very large numbers of traps are deployed and continually serviced. Thus, traps are of dubious value in protecting a given location [20-22].

●Toxic baiting programs for yellowjackets hold the greatest promise for success, but most aspects of their methodology are still under development [10,23-25]. Challenges that need to be solved to make this a viable approach include affordability, insecticide efficacy, exclusion of nontarget species, and sustainability of bait attractiveness.

AVOIDANCE OF STINGS FROM COLONIES

Risk factors for multiple stings — Large colonies are potentially capable of delivering hundreds, or even thousands, of stings almost instantaneously [26,27]. The single greatest risk factor for multiple stinging by a disturbed colony is simply being outdoors in a spot not frequented by humans. This typically implies an area with vegetation. Thus, the more time spent in natural locales (particularly off well-established paths), the higher the risk. For people who live and work in developed locations, activities in parks, yards, or gardens are most likely to bring them into accidental contact with a social bee or wasp nest.

Stimuli that elicit group defensive behavior — Group defensive behavior by a social wasp or bee colony may be elicited by considerably more subtle stimuli than the pressure of direct contact needed to provoke stinging from most individual foragers. In addition, many species use an alarm pheromone to rapidly recruit workers for defense during an emergency.

Typically, an abrupt movement of the nest (often due to vibration of its immediate surroundings) will trigger defensive behavior by a colony. Those activities producing vibration and disturbance to vegetation, such as accompanying a dog or mowing, pruning, or string trimming, are most likely to result in stinging [1,26]. Gasoline-powered lawn mowers have the distinction of being perhaps the most efficient means for stimulating wasp or bee colonies to attack. These machines are "the perfect predator" from the insects' point of view since they produce noise, vibration, odors, and heat [26]. However, in some cases, just nearby motion, the approach of a dark object, or mammalian breath is a sufficient stimulus [1,26,28-31].

Arousal thresholds and intensity of colony response — Arousal thresholds and intensity of aggressive response vary widely among social Hymenoptera and are dependent upon genetic lineage and a colony's age, size, and history of disturbance [1,28,29,32]. A colony that was previously aroused will often attack with far less provocation than one that has never been disturbed.

Personal avoidance measures — Practical risk avoidance measures are limited. Maintaining a continuous, effective level of vigilance for social wasp or bee colonies while outdoors is beyond the capability of many people. Those at greater risk from Hymenoptera stings should avoid activities that may disturb a colony, such as mowing the lawn or pruning a hedge.

Colony control and avoidance — The major problem universally posed by stinging insects is the cryptic nature of their nests, many of which are totally concealed in protected cavities either above or below ground. Even large, exposed nests in vegetation or attached to structures are typically obscured by foliage, overhangs, or shadow [28].

Preventive measures normally involve killing the workers (or sometimes capturing them, in the case of honey bees) and removing the nest if a social wasp or bee nest is observed in an undesirable location. This activity should not be attempted by anyone other than a licensed pest control professional who has received specialized training and is equipped with clothing designed specifically to protect against stings, even though insecticide products labeled for stinging insect control are readily available to the general public [3,4]. The process often requires extensive measures to protect the safety of bystanders [33,34]. The precise methodology of nest control operations is highly variable, depending upon species and circumstances, and is beyond the scope of this topic review.

Personal rescue actions — Outdoor activities are either difficult to avoid or highly pleasurable for many people. Thus, the most useful advice often involves a few commonsense guidelines for personal behavior once a nest is disturbed [26,30,31,35,36]:

●Persons who encounter/disturb a nest should slowly walk away from the area without flailing the arms if only a few bees or wasps are flying around them. Sudden motion often exacerbates attack behavior and increases the chance of accidental contact.

●Persons should cover their mouth and nose and run from the area without delay if many insects suddenly start to fly around them or if they are being stung. Stinging insects tend to target the facial area, which can quickly produce panic and disorientation in the victim.

●If possible, persons under attack by bees or wasps should seek shelter in a building or enclosed vehicle.

Mitigating the severity of attacks — Few readily deployed measures that might mitigate the intensity of social insect defensive reactions are available:

●Attacking bees and wasps are strongly attracted to dark colors (one reason why eyes, mouth, and nostrils are selectively targeted), so white or very light-colored clothing that covers most of the body should confer some advantage [30,31,35-37]. In addition, wearing a wide brim hat has been shown to effectively block many stings to the face and head [30,31].

●Mixed results have been reported on the efficacy of an aerosol spray of the common insect repellent N,N-diethyl-m-toluamide (DEET) in decreasing the magnitude of mass honey bee attacks [38,39].

●Smoke reduces defensive behavior in both honey bees and yellowjackets [37], although this would seem to have limited practical value in an unexpected confrontation.

●Persons with outdoor occupations that present an elevated risk for disturbing bee and wasp colonies have the option of carrying at least minimal protective equipment with them (eg, a compact mesh veil to cover the head). Firefighters in natural areas are urged to take refuge in a personal fire shelter (a standard protective item made from aluminum foil, fiberglass, and woven silica) in the case of severe stinging insect attack [35].

SUMMARY AND RECOMMENDATIONS

●Overview – The Hymenoptera is one of the largest insect orders, consisting of more than 150,000 species of wasps, bees, and ants, the vast majority of which are harmless to humans (figure 1). The females of one subgroup called the Aculeata have their ovipositor modified into a sting apparatus (vernacular, "stinger") capable of injecting venom that may produce an allergic reaction. Almost all cases of human stings are from social species that live in colonies. (See 'Overview' above.)

●Scenarios that provoke attacks – The most important concept of sting prevention is recognizing that there are two completely different scenarios in which worker bees or wasps are provoked to attack. The first involves single workers away from their nest, which typically are harmless unless directly touched. The second involves disturbing the nest of a colony, which typically results in defensive behavior of multiple workers, including stinging, even if the nest itself is not directly touched. (See 'Scenarios that provoke attacks' above.)

●Avoidance of stings from individual insects – Contrary to popular folklore, worker bees and wasps away from their nests are not aggressive toward humans and must be firmly touched before they will sting. Personal protection therefore largely involves heightened awareness in areas where these insects are abundant, particularly when eating or drinking. (See 'Avoidance of stings from individual workers' above and 'Personal behavior' above.)

•Brightly colored clothing and fragrance – There is no evidence that perfume or bright, floral-colored clothing attracts individual bees and wasps or elevates sting risk, despite widespread advice to the contrary. (See 'Wardrobe and cosmetic fragrance' above.)

•Reducing foraging – Sanitation measures that minimize food and food waste available to worker bees and wasps tend to be more effective in reducing their numbers than other methods. Toxic baiting techniques for area-wide abatement of foraging yellowjackets are still largely in the experimental stage. Available traps for these wasps typically do not capture sufficient workers to significantly reduce sting risk. (See 'Forager reduction' above.)

●Avoidance of stings from colonies – Preventing stings from colonies is more problematic than with individual foragers and depends mostly upon personal awareness when disturbing vegetation, particularly when doing yard work. (See 'Avoidance of stings from colonies' above.)

•Light-colored or white clothing – The most effective measure in mitigating the severity of a mass attack is probably the wearing of white or light-colored clothing while outdoors since attacking stinging insects are strongly attracted to dark colors. (See 'Mitigating the severity of attacks' above.)

•Personal rescue actions if a nest is encountered – Persons should back slowly away from the area without making any sudden movements if a few bees or wasps start flying around them. However, persons should cover their mouth and nose and run from the area and seek shelter in a building or enclosed vehicle if large numbers of insects begin flying around them or they are being stung. (See 'Personal rescue actions' above.)