Which insect can cause a sterile pustule that evolves over 6-24 hours and may cause necrosis and scarring?

Which insect can cause a sterile pustule that evolves over 6-24 hours and may cause necrosis and scarring?

• A. Fire ant
• B. Honey bee
• C. Mosquito
• D. Spider

Answer: (A)

The key idea is recognizing a venom-driven skin reaction that forms sterile pustules after a delay, a pattern classic for fire ant bites. Fire ant venom contains cytotoxic alkaloids that cause local tissue irritation and necrosis. Each sting can produce a small, sterile pustule that typically develops within 6–24 hours; these pustules are not caused by bacterial infection, which is why they are described as sterile. When many stings occur, the inflammation can be more extensive, sometimes leading to necrosis and scarring. This helps differentiate from other insects. Honey bee stings usually cause immediate sharp pain, swelling, and a wheal-and-flare reaction rather than sterile pustules. Mosquito bites lead to itchy, red papules that form quickly but are not the same sterile pustule pattern nor the necrosis-scarring trajectory. Spiders can cause necrotic ulcers as well, but the presentation and timing differ and aren’t the classic sterile pustule form caused by fire ant envenomation. So the combination of a sterile pustule developing within hours after stinging, with potential for local necrosis and scarring, points to fire ant bites.

The key idea is recognizing a venom-driven skin reaction that forms sterile pustules after a delay, a pattern classic for fire ant bites. Fire ant venom contains cytotoxic alkaloids that cause local tissue irritation and necrosis. Each sting can produce a small, sterile pustule that typically develops within 6–24 hours; these pustules are not caused by bacterial infection, which is why they are described as sterile. When many stings occur, the inflammation can be more extensive, sometimes leading to necrosis and scarring.

This helps differentiate from other insects. Honey bee stings usually cause immediate sharp pain, swelling, and a wheal-and-flare reaction rather than sterile pustules. Mosquito bites lead to itchy, red papules that form quickly but are not the same sterile pustule pattern nor the necrosis-scarring trajectory. Spiders can cause necrotic ulcers as well, but the presentation and timing differ and aren’t the classic sterile pustule form caused by fire ant envenomation.

So the combination of a sterile pustule developing within hours after stinging, with potential for local necrosis and scarring, points to fire ant bites.