There is often confusion in diagnosing spider bites. Most “spider bites” described by patients are actually folliculitis or furuncles; most spider bites are characterized by wheals, papules, or pustules. It is rare to see a punctum. Bites may itch or burn with most symptoms resolving in about 1 week. Bites may become secondarily infected from scratching.
Spider bites causing severe systemic symptoms are rare and are inflicted by a limited number of spiders. Each spider has a specific geographic distribution. For example, the brown recluse spider, Loxosceles reclusa, is found in the southern and central United States (Figure 60). Its bite can occasionally cause severe skin necrosis with significant pain and systemic symptoms.
Bees, wasps, and ants belong to the order Hymenoptera. Following a sting, the stinger should be removed to prevent continuing envenomation. About 10% of the general population experience large local reactions to stings that can be treated symptomatically. According to the 2016 American Academy of Allergy, Asthma & Immunology guideline, adults with only cutaneous systemic reactions (urticaria, flushing peripheral angioedema) or large local reactions are at low risk for anaphylaxis and typically do not need testing or venom immunotherapy (VIT). In patients with a noncutaneous severe systemic reaction, measuring baseline serum tryptase can identify patients at high risk for anaphylaxis, anaphylaxis during VIT, and recurrence following VIT, and those with mastocytosis. All patients with severe systemic reactions should carry self-injectable epinephrine and medical identification and be referred for testing and VIT. There is no consensus for prescribing self-injectable epinephrine in patients who experience only systemic cutaneous reactions or large local reactions.
Fire ants (Solenopsis invicta), which are mostly found in the southern United States, have sharp jaws and a posterior stinger. The ants latch with their jaws and repeatedly sting while rotating around the bite site, which results in a central papule ringed with pustules.
Cutaneous larva migrans results from hookworm penetration of bare skin. As the worm migrates through the skin, it leaves elevated serpiginous pruritic lesions (Figure 61). Wearing shoes outdoors (especially on the beach) prevents transmission from animal feces. Treatment is ivermectin, albendazole, or cryotherapy at the advancing edge of the eruption.
Fleas are the one of the most common causes of papular urticaria characterized by itchy papules on the legs and arms (Figure 62). The cat flea (Ctenocephalides felis) is the most common.