Insect Bite

Aka: Insect Bite, Arthropod Bite, Arthopod, Arachnid, Insect, Arthropod Dermatosis, Bug Bite

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II. Pathophysiology: Arthropod types

  1. Arachnids (8 legs)
    1. Spiders
      1. See Spider Bite
      2. Black Widow Spider (Lactodectus mactans)
      3. Brown Recluse Spider (Loxosceles reclusa)
      4. Precautions
        1. "Spider Bites" are typically not due to Spiders, but rather other causes (e.g. MRSA Cellulitis)
        2. Most Spider Bites are benign (not black widow or brown recluse)
          1. Need only minimal local therapy (Wound Cleansing, cold therapy)
    2. Mites
      1. Scabies
      2. Chiggers
    3. Scorpions
    4. Ticks
      1. See Tick Bite
      2. See Vector Borne Disease
  2. Insects (6 legs)
    1. Diptera (2-winged Insects)
      1. Mosquito
      2. Gnats
      3. Flies
      4. Sand Flies
      5. Midges
    2. Siphonaptera
      1. Fleas
    3. Hemiptera ("true bugs")
      1. Bed Bugs
    4. Psocodea
      1. Lice
    5. Hymenoptera (includes Stinging Insects)
      1. See Stinging Insect Bite
      2. Apidae (Bees)
        1. Honey bees
        2. Bumble bees
      3. Vespidae
        1. Wasps
        2. Yellow Jackets
        3. Hornets
      4. Formicidae (Stinging Ants)

III. Signs

  1. Most "Spider Bites" are due to some other cause
  2. Pruritic, Red Papules
    1. Typical Insect Bite (e.g. Mosquito Bite or biting midge such as no-see-ums, Sand Fly)
  3. Pruritic welts along constrictive clothing lines (waist band or sock line)
    1. Chigger Bite
  4. Clustered or linear Papules at the ankles
    1. Flea Bite

IV. Differential Diagnosis: Insect Bite Reaction

  1. See Annular Lesion
  2. See Stinging Insect Reaction
  3. Folliculitis
  4. Impetigo
  5. Cellulitis
  6. Shingles
  7. Contact Dermatitis
  8. Erythema Migrans
    1. Most Insect Bite reactions are localized (typically <2.5 to 5 cm in size) and resolves in first 48 hours
    2. Erythema Migrans insyead, continues to expand at >48 hours to diameters often >10 cm
  9. Erythema Multiforme
    1. Multiple target lesions each typically <2 cm diameter
  10. Granuloma Annulare
    1. Scaling erythematous lesions with central clearing (esp. hands and feet)
  11. Methicillin Resistant Staphylococcus Aureus (MRSA)
    1. Lesions with necrotic central eschar
  12. Tinea Corporis
  13. Urticaria

V. Complications

  1. Anaphylaxis or other serious Allergic Reaction
  2. Papular Urticaria
  3. Vector Borne Disease (e.g. Lyme Disease with Erythema Migrans)
  4. Cellulitis
    1. Inflammation out of proportion to Insect Bite
    2. Regional Lymphadenopathy
    3. Ascending lymphangitis

VI. Management: General

  1. Remove Stinger with forceps (avoid pinching the Stinger gland)
  2. Apply ice pack for 10-20 minutes per hour for 3 hours
    1. Contraindicated in Tarantula Bite
  3. Treat itch symptomatically
    1. Oral Benadryl for nighttime itch, Zyrtec for daytime itch
    2. Cool compresses
    3. Oral Analgesics (e.g. Acetaminophen or NSAIDs)
    4. Anti-irritant agents (e.g. sarna)
    5. Protective agents (e.g. calamine)
    6. Topical Corticosteroids (low potency such as 1% Hydrocortisone, brief use) may be considered
    7. Avoid topical Antihistamines (e.g. topical Benadryl) due to Contact Dermatitis risk

VII. Management: Acute Allergic Reaction

  1. See Anaphylaxis
  2. See Stinging Insect Allergy
  3. Prescribe Epi-Pen for emergency use for those with Anaphylaxis history

VIII. Management: Suspected Cellulitis

  1. See Cellulitis for Antibiotic selection
  2. Tetanus Prophylaxis

IX. Prevention

  1. See Prevention of Vector-borne Infection
  2. Check clothes for Insects before donning
  3. Avoid times of peak Insect activity (dawn and dusk)
  4. Avoid habitats
    1. Woodpiles
    2. Crawl spaces
    3. Corners of buildings
    4. Standing water
    5. Dense vegetation
  5. Dress for working outdoors
    1. Keep skin covered by clothing
      1. Wear gloves
      2. Shirt tucked into pants
      3. Pants tucked into socks
      4. Wear a hat and high collar
      5. Avoid loose clothing
    2. Avoid Insect attractants
      1. Avoid bright colors (wear light colored clothing)
      2. Avoid perfumes
  6. Insect Repellents
    1. See Insect Repellent
    2. DEET (<30% is safe in young children)
      1. Mosquitoes
      2. Fleas
      3. Gnats
      4. Chiggers
    3. Permethrin (Elimite, Nix) on clothes
      1. Ticks

X. References

  1. Norris (1998) Physician and Sports Med 26(7):47-58
  2. Herness (2022) Am Fam Physician 106(2): 137-47 [PubMed]
  3. Juckett (2013) Am Fam Physician 88(12): 841-7 [PubMed]
  4. Kemp (1998) Postgrad Med 103(6):88-106 [PubMed]

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