Insect Bites Clinical Presentation

Updated: Oct 13, 2021
  • Author: Boyd (Bo) D Burns, DO, FACEP, FAAEM; Chief Editor: Joe Alcock, MD, MS  more...
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Most patients are aware of insect bites when they occur or shortly thereafter, but because it is such a common occurrence, the exposure is typically dismissed unless a severe or systemic reaction occurs.

Reactions to bites may be delayed due to the host being asleep or because the saliva of some micropredators may contain an anesthetic secreted to allow uninterrupted blood-feeding.

Patients who present with a history of homelessness or of staying in homeless shelters may have an exposure to organisms such as bedbugs. [4, 16, 17] Alternatively, patients with impairment from mental illness may also be susceptible to infestation with insect parasites.

Exposure to feral animals or even to domesticated animals, such as livestock or house pets, may predispose patients to exposure to biting insects such as fleas, bedbugs, [4, 18, 17] or lice.

Types of reactions

In a local reaction, the patient may complain of discomfort, itching, moderate or severe pain, erythema, tenderness, warmth, and edema of tissues surrounding the site. Although it may involve neighboring joints, local reactions cause no systemic symptoms.

In a severe local reaction, complaints include generalized erythema, urticaria, and pruritic edema. Severe local reactions increase the likelihood of serious systemic reactions if the patient is exposed again at a later time.

In a systemic or anaphylactic reaction, the patient may complain of localized symptoms as well as symptoms not contiguous with the bite location. Symptoms can range from mild to fatal. Early complaints typically include generalized rash, urticaria, pruritus, and angioedema. These symptoms may progress, and the patient may develop anxiety, disorientation, weakness, gastrointestinal disturbances (eg, cramping, diarrhea, vomiting), uterine cramping in women, urinary or fecal incontinence, dizziness, syncope, hypotension, stridor, dyspnea, or cough. As the reaction progresses, patients may experience respiratory failure and cardiovascular collapse. [19]

Delayed reactions may appear 10-14 days after a sting. Symptoms of delayed reactions resemble serum sickness and include fever, malaise, headache, urticaria, lymphadenopathy, and polyarthritis.


Physical Examination

Without a clear patient history, diagnosis of an insect bite can be difficult since the initial response may be limited to erythema, local pain, pruritus, or edema.

Wheals and urticaria are common initial signs and generally appear within a few minutes of the bite. Unfortunately, many dermatologic conditions also produce similar cutaneous signs and may confound the diagnosis.

Identification of the insect responsible for the bite may be possible by examining the location, number, pattern, and sequelae of the bite(s).

Clinical criteria for diagnosis of anaphylaxis according to the World Allergy Organization are shown in the image below.

Insect Bites. World Allergy Organization anaphylax Insect Bites. World Allergy Organization anaphylaxis pocket card. Reprinted from The Journal of Allergy and Clinical Immunology, Vol 127, Issue 3, Simons FER et al, World Allergy Organization anaphylaxis guidelines; Summary, Pgs 587-93, March 2011, with permission from Elsevier. Available at