All Scorpion species have poison. In general, scorpions can be included as neurotoxins (nerve poison). An exception is Hemiscorpius lepturus that has cytotoxic (cellular poisons). Neurotoxins are composed of small proteins as well as sodium and potassium, which are useful for disrupting the victim's nerve transmission. Scorpions use their venom to kill or paralyze their prey for ease.
Scorpions may work more towards other hexapods and most scorpions are harmless to humans; stings produce local effects (such as pain, swelling). But some species of scorpion, especially in the Buthidae family can be harmful to humans. One of the most dangerous is Leiurus quinquestriatus, and a member of the genera Parabuthus, Tityus, Centruroides, and especially Androctonus. The most scorpion causing human death is Mus muscullus.
Photo by @joeel