Overview
Insect Bites and Stings
Quick Reference
Critical Alerts
- Anaphylaxis is the most serious complication: Requires epinephrine
- Most bites/stings cause local reactions: Self-limited
- Black widow and brown recluse spiders cause significant envenomation
- Tick bites may transmit disease: Lyme, Rocky Mountain spotted fever
- Remove stingers and ticks promptly: Reduces venom/pathogen load
- Prescribe epinephrine auto-injector after anaphylaxis: Allergy referral
Anaphylaxis Signs
| System | Signs |
|---|---|
| Skin | Urticaria, pruritus, flushing |
| Respiratory | Stridor, wheezing, dyspnea |
| Cardiovascular | Hypotension, syncope |
| GI | Nausea, vomiting, cramping |
Emergency Treatments
| Condition | Treatment |
|---|---|
| Anaphylaxis | Epinephrine 0.3-0.5 mg IM + Antihistamines + Steroids |
| Local reaction | Ice, elevation, antihistamines, NSAIDs |
| Black widow | Opioids, benzodiazepines, ± antivenom |
| Brown recluse | Supportive, wound care |
| Tick bite (no rash) | Remove tick, observe |
| Tick bite with EM rash | Doxycycline 100 mg BID × 10-21 days |
Definition
Overview
Insect bites and stings are extremely common. Most cause only local reactions (pain, swelling, itching). Some can cause systemic allergic reactions including anaphylaxis. Certain spiders (black widow, brown recluse) cause significant envenomation. Tick bites may transmit infectious diseases. Management ranges from supportive care to life-saving intervention for anaphylaxis.
Classification
By Type:
| Type | Examples |
|---|---|
| Stinging (Hymenoptera) | Bees, wasps, hornets, fire ants |
| Biting insects | Mosquitoes, flies, fleas, bedbugs |
| Spiders | Black widow, brown recluse, tarantula |
| Ticks | Ixodes, Dermacentor, Amblyomma |
| Scorpions | Bark scorpion (Centruroides) |
Epidemiology
- Very common: Millions of cases/year
- Hymenoptera stings: 40+ deaths/year in US (anaphylaxis)
- Tick-borne illness: ~50,000 cases/year (Lyme, RMSF)
- Spider bites often misdiagnosed: True bites less common than perceived
Pathophysiology
Venom Effects
Hymenoptera (Bees, Wasps):
- Venom contains histamine, phospholipase, hyaluronidase
- IgE-mediated allergy in sensitized individuals
- Anaphylaxis risk with re-exposure
Black Widow (Latrodectus):
- α-Latrotoxin causes massive neurotransmitter release
- Muscle pain, rigidity, autonomic effects
Brown Recluse (Loxosceles):
- Sphingomyelinase D causes dermonecrosis
- Hemolysis, systemic effects in rare cases
Ticks:
- Vector for infectious diseases (Lyme, RMSF, Ehrlichia, Babesia)
- Tick paralysis (rare): Neurotoxin in saliva
Clinical Presentation
Hymenoptera Stings
Local Reaction:
| Feature | Description |
|---|---|
| Pain | Immediate |
| Swelling | Localized, may be extensive (<10 cm) |
| Erythema | Around sting site |
| Itching | Common |
Large Local Reaction:
Systemic/Anaphylactic Reaction:
Spider Bites
Black Widow:
| Feature | Timing |
|---|---|
| Initial bite pain | Mild, pinprick |
| Muscle cramps, rigidity | Within 1-8 hours |
| Abdominal rigidity | "Boardlike" abdomen |
| Hypertension, diaphoresis | Autonomic effects |
Brown Recluse:
| Feature | Timing |
|---|---|
| Initial bite | May not be felt |
| Erythema, pain | Within 2-8 hours |
| Central necrosis | 3-7 days; "volcano lesion" |
| Systemic (rare) | Fever, hemolysis, DIC |
Tick Bites
Local:
Tick-Borne Illness:
| Disease | Findings |
|---|---|
| Lyme disease | Erythema migrans (EM) rash, flu-like illness |
| Rocky Mountain spotted fever | Fever, headache, petechial rash (starts on wrists/ankles) |
| Ehrlichiosis/Anaplasmosis | Fever, headache, leukopenia, thrombocytopenia |
| Babesiosis | Fever, hemolytic anemia, splenomegaly |
Swelling >10 cm, lasting >24 hours
Common presentation.
Contiguous with sting site
Common presentation.
NOT anaphylaxis (no systemic symptoms)
Common presentation.
Red Flags
Anaphylaxis
| Finding | Action |
|---|---|
| Urticaria + respiratory symptoms | Epinephrine IM |
| Hypotension, syncope | Epinephrine, IV fluids |
| Angioedema (lips, tongue, throat) | Epinephrine, airway management |
Severe Envenomation
| Finding | Concern |
|---|---|
| Black widow: Severe muscle rigidity, hypertensive crisis | Consider antivenom |
| Brown recluse: Expanding necrosis, hemolysis | Supportive, wound care |
| RMSF: Petechial rash, fever, headache | Immediate doxycycline |
Differential Diagnosis
Other Causes of Similar Lesions
| Diagnosis | Features |
|---|---|
| Cellulitis | Spreading erythema, warmth, fever |
| Abscess | Fluctuance, pus |
| Contact dermatitis | Linear, pruritic, history of exposure |
| MRSA skin infection | Purulent, abscess formation |
| Necrotizing fasciitis | Rapid spread, disproportionate pain |
Diagnostic Approach
Clinical Diagnosis
- Most bites/stings are clinical diagnoses
- History of exposure + typical findings
Laboratory (If Systemic)
| Test | Indication |
|---|---|
| CBC | Black widow (leukocytosis), RMSF (thrombocytopenia), babesiosis (anemia) |
| CMP | Renal function, electrolytes |
| CK | Black widow (rhabdomyolysis rare) |
| LDH, haptoglobin, bilirubin | Hemolysis (brown recluse, babesiosis) |
| Lyme serology | If EM rash present (clinical diagnosis); serology for later stages |
Imaging
- Not routinely needed
- Consider if abscess suspected
Treatment
Principles
- Recognize and treat anaphylaxis immediately: Epinephrine
- Remove stinger/tick promptly
- Supportive care for most local reactions
- Specific treatments for envenomation and tick-borne illness
Hymenoptera Stings
Local Reaction:
| Intervention | Details |
|---|---|
| Remove stinger | Scrape off (don't squeeze) |
| Ice | 20 min on, 20 min off |
| Antihistamines | Diphenhydramine 25-50 mg or cetirizine 10 mg |
| NSAIDs | Ibuprofen 400-600 mg for pain |
| Topical steroids | Hydrocortisone 1% for itching |
Large Local Reaction:
- Same as above
- Oral steroids may help (prednisone 40-60 mg × 3-5 days)
Anaphylaxis:
| Intervention | Details |
|---|---|
| Epinephrine IM | 0.3-0.5 mg (1:1,000) mid-lateral thigh |
| IV fluids | NS or LR for hypotension |
| Antihistamines | Diphenhydramine 25-50 mg IV + Famotidine 20 mg IV |
| Steroids | Methylprednisolone 125 mg IV |
| Repeat epinephrine | q5-15 min if needed |
| Observation | 4-6 hours for biphasic reaction |
Black Widow Bite
| Intervention | Details |
|---|---|
| Pain control | IV opioids |
| Muscle relaxants | Benzodiazepines (diazepam 5-10 mg IV) |
| Antivenom | For severe cases (Latrodectus antivenom) |
| Local wound care | Clean, ice |
| Tetanus | Update if needed |
| Antihypertensives | If severe hypertension |
Brown Recluse Bite
| Intervention | Details |
|---|---|
| Wound care | Clean, elevate |
| Ice | May limit necrosis |
| Tetanus | Update if needed |
| Pain control | NSAIDs, opioids |
| Antibiotics | Only if secondary infection |
| Surgery | Delayed debridement if significant necrosis |
No Proven Specific Antivenom or Treatment
Tick Bites
Tick Removal:
- Use fine-tipped tweezers
- Grasp close to skin, pull straight up
- Clean area
Prophylaxis for Lyme (If Criteria Met):
| Criteria | Prophylaxis |
|---|---|
| Ixodes tick attached ≥36 hours | Doxycycline 200 mg × 1 |
| In endemic area | |
| Within 72 hours of removal |
Lyme Disease (Erythema Migrans):
| Agent | Dose | Duration |
|---|---|---|
| Doxycycline | 100 mg BID | 10-21 days |
| Amoxicillin | 500 mg TID | 14-21 days (if doxycycline contraindicated) |
Rocky Mountain Spotted Fever:
| Agent | Dose | Duration |
|---|---|---|
| Doxycycline | 100 mg BID | Until afebrile × 3 days (typically 5-7 days) |
| Do not delay for confirmation | Empiric treatment if suspected |
Disposition
Discharge Criteria
- Local reaction controlled
- No systemic symptoms
- Able to take oral medications
- Educated on warning signs
Admission Criteria
- Anaphylaxis (observe 4-6 hours minimum)
- Severe black widow envenomation
- Brown recluse with systemic symptoms
- RMSF or other severe tick-borne illness
- Unable to tolerate oral intake
Referral
| Indication | Referral |
|---|---|
| Anaphylaxis history | Allergy for testing, Epi-Pen |
| Brown recluse necrosis | Wound care, surgery |
| Lyme with complications | Infectious disease |
Patient Education
Condition Explanation
- "You had an allergic reaction to the sting, but most bites cause only local swelling."
- "If you've had a severe reaction, you need to carry an epinephrine auto-injector."
Prevention
- Avoid fragrances and bright colors outdoors
- Wear protective clothing in tick-prone areas
- Use insect repellent (DEET, picaridin)
- Check for ticks after outdoor activity
- Do not disturb bee/wasp nests
Warning Signs to Return
- Difficulty breathing
- Swelling of lips, tongue, or throat
- Dizziness or fainting
- Widespread rash or hives
- Fever or flu-like symptoms after tick bite
- Expanding redness or new symptoms at bite site
Special Populations
Children
- Anaphylaxis presents similarly to adults
- Weight-based epinephrine dosing
- Tick-borne illness may present atypically
Pregnancy
- Epinephrine is safe and should be given for anaphylaxis
- Doxycycline contraindicated (use amoxicillin for Lyme)
- RMSF: Doxycycline may still be used if life-threatening
Immunocompromised
- Higher risk of severe tick-borne illness
- Lower threshold for admission
Quality Metrics
Performance Indicators
| Metric | Target | Rationale |
|---|---|---|
| Epinephrine for anaphylaxis | 100% | Life-saving |
| Epi-Pen prescribed after anaphylaxis | 100% | Prevention |
| Doxycycline for suspected RMSF | 100% | Time-sensitive |
| Tick removal documented | 100% | Standard of care |
Documentation Requirements
- Type of insect/spider/tick
- Time of bite/sting
- Local vs systemic symptoms
- Anaphylaxis features
- Treatment given
- Epi-Pen prescribed (if indicated)
- Follow-up plan
Key Clinical Pearls
Diagnostic Pearls
- Anaphylaxis = Systemic symptoms away from sting site: Not just local swelling
- Brown recluse: Often not witnessed: Consider differential
- Black widow: "Boardlike" abdomen, muscle cramps
- EM rash = Lyme: Treat clinically, serology not needed early
- RMSF: Fever + petechial rash: Treat immediately, don't wait for labs
- Tick must be attached ≥36h to transmit Lyme: Prophylaxis guidelines
Treatment Pearls
- Epinephrine IM is first-line for anaphylaxis: Don't delay
- Remove stinger by scraping: Don't squeeze
- Ice and antihistamines for local reactions
- Doxycycline single dose for Lyme prophylaxis: If criteria met
- Treat RMSF empirically: Delay increases mortality
- Black widow: Benzos and opioids: Antivenom for severe cases
Disposition Pearls
- Observe 4-6 hours after anaphylaxis: Biphasic reactions
- Prescribe Epi-Pen after anaphylaxis: And refer to allergy
- Admit severe envenomation or tick-borne illness
- Educate on prevention and warning signs
References
- Reisman RE. Insect Stings. N Engl J Med. 1994;331(8):523-527.
- Mowry JB, et al. 2020 Annual Report of the American Association of Poison Control Centers. Clin Toxicol. 2021;59(12):1282-1501.
- Wormser GP, et al. The Clinical Assessment, Treatment, and Prevention of Lyme Disease. Clin Infect Dis. 2006;43(9):1089-1134.
- Bitnun A, et al. Rocky Mountain spotted fever. Lancet Infect Dis. 2007;7(10):672-680.
- Wright SW, et al. Clinical presentation and outcome of brown recluse spider bite. Ann Emerg Med. 1997;30(1):28-32.
- Clark RF, et al. Clinical presentation and treatment of black widow spider envenomation: a review. Ann Emerg Med. 1992;21(7):782-787.
- Sampson HA, et al. Symposium on the definition and management of anaphylaxis. J Allergy Clin Immunol. 2005;115(3):S584-S591.
- UpToDate. Bee, wasp, and other Hymenoptera stings: Reaction types and acute management. 2024.