With the approach of warmer weather the incidence of patients presenting to Hospital Emergency Rooms with insect stings increases dramatically. The 6 major stinging insects in the United States are Fire ants, Bumble Bees, Honey Bees (including “Africanized” strains), Yellow Jackets, Hornets, and Wasps. The latter 5 are all classified as Bees, belonging to the order Hymenoptera. Bumble Bees and Honey Bees are in the family Apidae, while Yellow Jackets, Hornets, and Wasps are in the family Vespidae.

Wasps fall into three broad varieties; colonial nest builders, individual mud daubers, and solitary ground dwellers. In contrast to Hornets and Honey Bees whose colonies may number upwards of 50,000 insects, Wasp colonies number relatively few individuals, often no more than 10 adults, but may in the case of long established nests number into the thousands. These Wasp Nest builders form discreet open hive colonies usually located under housing eaves, but may be found attached under benches, overturned outdoor furniture, unused grills, or any above ground site that is dry, and relatively protected from rain, or molestation by animals. Ground dwelling wasps and mud dauber wasps are by contrast solitary, living in burrows or mud “pipes” housing the egg laying parent and her 5 to 25 offspring.

As members of the order Hymenoptera Wasps have envenomed stingers that may cause a variety of responses from small or large localized reactions, to anaphylaxis, serum sickness or venom intoxication. The later three may lead to hypotension, systemic organ failure, collapse, and death. Twice as many people die from Hymenoptera stings than die from snake bites in this country, about 40 annually. Most stinging incidents are chance encounters with solitary foraging bees who become trapped or entangled in their contact with a person. While even a single sting for the first time may result in life threatening anaphylaxis, the actual incidence is less than 3 in one thousand. However, in those incidents where people are injured, they most often involve encounters with colonial or social Bee’s & Wasp’s Nests and may result in multiple stings with massive envenomation. While Yellow Jackets are the most aggressive, and the scourge of sugar laden field picnics, they tend to be fringe field and forest burrowers, thus come into contact only with people who noisily intrude into their territory. Similarly, Hornets and wild Honey Bee nests are usually located away from human habitations. It is Wasp colonies however, who by nesting under housing eaves and in proximity to human dwellings and possessions, that are most likely to make aggressive defensive contact with people.

The Hymenoptera stinger is a modified egg laying apparatus at the posterior thorax, composed of a stinger shaft containing a stationary stylet and two sliding barbed lancets, which together form a hollow channel through which venom may be delivered. Muscles in the stinger apparatus slide the lancets back and forth along the fixed stylet shaft, burrowing the barbs into the skin, and holding that contact long enough to inject the venom hypodermically, by pumping it into the tissues reached by the barbed lancets. Wasp stingers have short barbs which burrow but do not embed in tissue, and as a result may be easily removed by the sliding action, so that Wasps may sting multiple times without harm to themselves.

The biodiversity of Wasp species is great although most stinging events are attributed to the colonial genera Vespa, Vespula, and Dolichovespula. Their venom’s are just as diverse due to the above phylogenetic differences but also to the different functions that their venom is employed to serve. Wasps use their venom in colony defense, offensively against prey to be consumed, and as a method for immobilizing live prey, into whom they secrete their eggs, and which then allows their emerging offspring to feed on the living tissues free from molestation. Generally wasp venom is a dynamic biological ’soup’ that contains active amines like : serotonin : histamine: tyramine : pain kinins (like bradykinins) : catecholamines : mastoparans (histamine triggering peptides) : weak allergens like phospholipase A, B, & hyaluronidase, and the most active allergen # 5.  Acetyl-Choline & Neurotoxins may also be found in some species’ venom, as may a suspected nephrotoxin.

Wasp venom disrupts mammalian cell membranes, releasing cellular components, altering ion channels, triggering inappropriate nerve depolarization, and stimulating extensive pain, but often causing little real tissue damage, except when the toxic effects of accumulated venom from multiple stings causes widespread hemolysis, rhabdomyolysis, & direct tissue necrosis, with resulting tissue & organ failures. Initial toxic responses may include diaphoresis, malaise, nausea, vomiting, & diarrhea. Renal damage often from protein byproducts of hemolysis & rhabdomyolysis, is the most common toxic outcome, usually occurring in the first 24 hr. Death from renal failure & cardiac arrest have occured from 4 hours to 9 days after envenomation. recovery may take three to six weeks. The lethal dose of wasp venom (apart from allergic anaphylaxis) varies by species. Vespa species can deliver large venom doses with half of fatalities occuring at 1.6 to 4.2 mg/kg and might involve as few as 50 stings. Smaller Vespula species are common to the U.S. deliver less venom amounts, and that venom is itself less potent, with fatalities occuring between at 3.5 to 15 mg/kg involving more than 200 stings. Treatment of toxic envenomation from Wasp stings involves supportive respiratory, renal, & cardiac care, may require serial dialysis, venom immunotherapy, and immune modulation. Recovery may be from 3 to 6 weeks long.

None the less the vast majority of Wasp sting incidents, 997 of every thousand, are benign, with typical symptoms of proximal localized swelling, pruritis, pain, and erythema. These resolve rapidly in 24 hours and respond well to ice, analgesics, & dilute anti itch sticks (ammonia, ascorbate, or baking soda) application. Larger local reactions, with swelling that peaks in 24 to 48 hours and may last up to 10 days are also among these commonoccurrences. These more severe local symptoms are often accompanied by swelling fatigue malaise & nausea; and may be mistaken for cellulitis or secondary infection. ICE, NSAIDS, antihistamines, and corticosteroids whether injected or oral are helpful in resolving these symptoms without further sequelae.

The incidence of Anaphylaxis from Wasp stings is less then 0.3% to 3% in general populations. IgE mediated symptoms appear within 1 to 30 minutes as expanding dermal swelling, general urticaria, hives, flush, and angioedema. These may rapidly progress to life threatening degree with wheeze, larygospasm, respiratory distress, bronchial edema, hypotension, circulatory collapse, irreversible airway obstruction, shock, and death. A majority of anaphylactic deaths are in older individuals with comorbidities (like heart or lung disease), but may occur in any age group. Anaphylaxis recurs in subsequent stings for only about 60% of affected individuals, there is NO predicting who will or will not recur for each incidence. Anaphylaxis is best treated with rapid subcutaneous administration of Epinephrine, followed immediately by Intramuscular injection of high potency steroids, and high potency antihistamines, inhaled bronchodilators may also be used as adjuvant therapy. This should be followed with a 7 day course of oral steroids, antihistamines, and topical steroid cream to the insect sting; as the incidence of relapse out to x1 week post sting has been documented. Immunological (RAST) testing and venom immunotherapy are prophylactic measures to prevent subsequent attacks. Especially sensitive individuals should carry an epi-pen kit, oral antihistamines, and steroids when in high risk environments; and should further take mechanical precautions to prevent stings - long pants, sleeves, boots, gloves, hat, avoid bright clothes, sugary drinks and foods, scents & perfumes, wear insect repellent.

Less common (under 0.1%) are serum sickness type reactions involving arthralgia, urticaria, joint pain, & fever occurring a week to 10 days after Wasp sting exposure, lesser still are immune mediated vasculitis, nephrosis, neuritis, and encephalitis that have a temporal relationship to the sting. Treatment for all these conditions is expectant and involves corticosteroids, NSAIDS, antihistamines, and more rarely still respiratory & cardiac supportive care. Although the incidence of secondary infection from insect stings is low, possible seeding of the sting site with bacteria via pruritic excoriation shortly after the incident is still a possibility.  Expectant observation and wound hygiene with providone Iodine solutions should be sufficient to prevent secondary infection. However, in rare instances such a wound may become infected & abscessed in which case incision & drainage, then treatment with a Staphylococcus specific and a mixed polymicrobial antibiotic may be necessary. While acquiring tetanus from an insect sting is highly unlikely, it is advisable to update one’s tetanus vaccination should it be out of date (more than 10 years), or in the event of a subsequent abscess from secondary infection.

In summary with the approach of warm weather, to avoid Wasp stings one should exercise an ounce of prevention. Dress appropriately, wear insect repellents, avoid or spray Wasp nests around the home, then remove them from your domestic proximity. Ensure your vaccinations are up to date, and if you are an anaphylactic prone individual keep emergency medication and the number of an urgent care clinic handy.