Though the pain of various insect stings might feel mostly the same to you, albeit varying in intensity, different venoms act on different molecular pathways. Your neurons have all sorts of receptors and channels dotting their surface, and some of them activate a pain response. Animals and plants take advantage of these pathways by producing molecules that activate that pain response, sometimes by activating a specific channel in mammalian neurons or blocking another one. Peppers and horseradish are both spicy, for instance, but the chemicals that make them taste fiery work differently. Capsaicin makes peppers hot, but horseradish (and wasabi) contain something called allyl isothiocyanate, or AITC. Each acts on a different receptor, even though you feel a similar kind of pain.