What key difference separates the immediate sensation of a fire ant sting versus contact with a *Paederus* beetle?

Fire ant stings are immediately painful; the beetle reaction begins hours later.

Differentiating the source of skin irritation is often reliant on the temporal sequence of symptoms, providing a crucial diagnostic clue. A true venomous sting, such as from a fire ant, involves an immediate injection of venom causing acute, sharp pain right at the moment of impact, often resulting in a localized welt that quickly progresses to a pustule. In stark contrast, contact with a *Paederus* beetle is generally painless at the time of contact, often going unnoticed until the chemical injury manifests hours later as flat, red erythema. This profound temporal difference—immediate pain versus delayed eruption—is a practical tool used to distinguish a venomous sting reaction from the chemical contact dermatitis induced by pederin.