The only insects that can truly sting are bees, wasps and ants, and then just the social species (living together in colonies).
Ants and Bees
Formic acid and methanioc acid
My educated guess is that the theory of "Likes dissolves likes", insect stings are acid bases... therefore another form of acid would neutralize the insects acid. hope this helps.
Acid
Dock leaves are alkaline - they neutralise the formic acid in nettle stings
formic acid
Acidic
if you put vinegar on wasp stings it will help because wasp stings have alkali in it and vinegar is a weak acid but bee stings are different they are acidic so if you put toothpaste on it it will help (try not to get bee stings mixed up with wasp stings because it will hurt even more if you put toothpaste on wasp stings or vinegar on bee stings)
Yes they do.
They are alkali, hence the use of vinegar to neutralize the stings.
Formic acid, also known as methanoic acid. HCOOH.
acid
Formic acid.