Scorpions have two ways of subduing prey: crushing it with the pedipalps, the pincer-bearing appendages at the front, or injecting venom through the sting at the tail tip. Emperor scorpions have massive, heavily built pincers and rely on them heavily. Species with thin, delicate pincers cannot overpower prey mechanically and depend far more on potent venom.
The result is a broad inverse pattern across the order. The emperor scorpion, at up to about 20 centimetres and 30 grams, produces a sting that in adults is typically described as painful but medically minor, roughly comparable to a wasp or bee sting. The species that cause serious human envenomation are overwhelmingly in the family Buthidae, and most are far smaller and more lightly built.
The pattern is a tendency, not a law, and individual reactions vary. Allergic responses to any scorpion sting can be severe regardless of the venom's baseline toxicity, and venom composition within a species can differ by population and by age.