Stinging insects (eg, bees, wasps, fire ants) are members of the order Hymenoptera of the class Insecta. Hymenoptera venoms cause local toxic reactions in all people and allergic reactions only in those previously sensitized. Severity depends on the dose of venom and degree of previous sensitization. Patients exposed to swarm attacks and patients with high venom-specific IgE levels are most at risk of anaphylaxis; many children never outgrow the risk. The average unsensitized person can safely tolerate 22 stings/kg body weight; thus, the average adult can withstand > 1000 stings, whereas 500 stings can kill a child (1).
Large numbers of people seek medical attention for stings and their complications after hurricanes and other environmental disasters.
Major Hymenoptera subgroups are
Apids (eg, honeybees, bumblebees)
Vespids (eg, wasps, yellow jackets, hornets)
Formicids (eg, fire ants, harvester ants, oak ants)
Apids usually do not sting unless provoked; however, Africanized honeybees (killer bees), migrants from South America that reside in the south and southwest of the United States, are especially aggressive when agitated. Apids typically sting once and dislodge their barbed stinger into the wound, introducing venom and killing the insect. Melittin is thought to be the main pain-inducing component of the venom. The venom of Africanized honeybees is no more potent than that of other honeybees but causes more severe consequences because these insects attack in swarms and inflict multiple stings, increasing the dose of venom. In the United States, hornet, wasp and bee stings cause around 70 deaths per year (2).
Image courtesy of Justin Kaplan, MD.
Vespid stingers have few barbs and do not stay in the skin, so these insects can inflict multiple stings. The venom contains phospholipase, hyaluronidases, and the antigen 5 protein, which is the most allergenic. Although vespids also avoid stinging unless provoked, they nest close to humans, so provocative encounters are more frequent. Yellow jackets are the major cause of allergic reactions to insect stings in the United States.
ALAN SIRULNIKOFF/SCIENCE PHOTO LIBRARY
Fire ants (refers to several species of ants, all part of the genus Solenopsis) are present in the southern United States, particularly in the Gulf region, where in urban areas, they may sting as many as 40% of the population, causing at least 30 deaths/year. There are several species, but Solenopsis invicta predominates and is responsible for an increasing number of allergic reactions. The ant bites to anchor itself to the person and stings repeatedly as it rotates its body in an arc around the bite, producing a characteristic central bite partially encircled by a reddened sting line. The venom has hemolytic, cytolytic, antimicrobial, and insecticidal properties; 3 or 4 small aqueous protein fractions are probably responsible for allergic reactions.
References
1. USDA Agricultural Research Service. U.S. Department of Agriculture: Carl Hayden Bee Research Center. Bee Stings. Accessed December 12, 2024.
2. QuickStats: Number of Deaths from Hornet, Wasp, and Bee Stings* Among Males and Females - National Vital Statistics System, United States, 2011-2021. MMWR Morb Mortal Wkly Rep. 2023 Jul 7;72(27):756. doi: 10.15585/mmwr.mm7227a6. PMID: 37410668; PMCID: PMC10328479.
Symptoms and Signs of Insect Stings
Local apid and vespid reactions are immediate burning, transient pain, and itching, with an area of erythema, swelling, and induration up to a few centimeters across. Swelling and erythema usually peak at 48 hours, can persist for a week, and can involve an entire extremity. This local chemical cellulitis is often confused with secondary bacterial cellulitis, which is more painful and uncommon after envenomation. Allergic reactions may manifest with urticaria, angioedema, bronchospasm, refractory hypotension, or a combination; swelling alone is not a manifestation of allergic reaction.
Symptoms and signs of a fire ant sting are immediate pain followed by a wheal and flare lesion, which often resolves within 45 minutes and gives rise to a sterile pustule, which breaks down within 30 to 70 hours. The lesion sometimes becomes infected and can lead to sepsis. In some cases, an edematous, erythematous, and pruritic lesion, rather than a pustule, develops. Anaphylaxis due to fire ant stings is probably rare. Mononeuritis and seizures have been reported.
Diagnosis of Insect Stings
History and physical examination
Diagnosis of insect stings is clinical.
Apid stings are checked for the stinger, which may remain behind in the wound.
Upper and lower airways are assessed for signs of allergic reaction.
Secondary bacterial cellulitis is rare but is considered when erythema and swelling begin a day or two after the sting (rather than immediately), there are systemic signs of infection (eg, fever, chills), and pain is significant.
Treatment of Insect Stings
Parenteral epinephrine and antihistamines for systemic allergic reactions
Removal of any apid stingers
Analgesics and antihistamines for local reactions
Stingers, if present, should be removed as quickly as possible. Suggested methods include scraping with a thin dull edge (eg, edge of a credit card, dull side of a scalpel, thin table knife).
Mild symptoms pain, burning, and itching can be reduced by placing an ice cube wrapped in a cloth over the sting as soon as possible and giving oral antihistamines, nonsteroidal anti-inflammatory drugs (NSAIDs), or both. Other possibly effective local measures include topical lotions, lidocaine patches, eutectic mixture of local anesthetic cream, intradermal injection of 1% lidocaine (with or without 1:100,000 epinephrine), and mid-potency corticosteroid creams or ointments (eg, triamcinolone 0.1%). Most folk remedies (eg, application of meat tenderizer) are of limited effectiveness.
Moderate allergic reactions are treated with IV antihistamines; anaphylaxisis treated with parenteral epinephrine and IV fluids and vasopressors if necessary.
People with known hypersensitivity to stings should carry a kit containing a prefilled self-injecting syringe of epinephrine and oral antihistamines for prompt self-treatment after exposure. They should use it as soon as possible after a sting and seek medical care immediately. People who have a history of anaphylaxis or a known allergy to insect bites should wear identification such as an alert bracelet.
Prevention of Insect Stings
People who have had anaphylaxis are at risk from subsequent insect stings. Desensitization immunotherapy can be considered. For example, venom immunotherapy is highly effective in reducing the chance of recurrent anaphylaxis from fire ant stings (1). Venom immunotherapy seems to be safe for use during pregnancy. Single-venom therapy is adequate. After initial immunotherapy, maintenance doses may be needed for up to 5 years.
Prevention reference
1. Neaves BI, Coop CA. Imported fire ant immunotherapy. Ann Allergy Asthma Immunol. 2024;133(1):28-32. doi:10.1016/j.anai.2024.01.014
Key Points
Apid and vespid stings cause immediate pain, burning, itching, erythema, and swelling.
Fire ant stings cause immediate pain, wheal, and flare, often followed by a pustule within an hour and sometimes infection within hours or days.
Suspect secondary infection when significant pain, a delay of a day or 2 in erythema and swelling, or systemic findings occur.
Suspect an allergic reaction when urticaria, angioedema, bronchospasm, and/or refractory hypotension occurs, but not with swelling alone.
Remove apid stingers and treat local reactions with ice, oral H1 blockers, and/or NSAIDs.
Treat allergic reactions and infections.
Consider desensitization immunotherapy for patients with anaphylactic reactions.
