I agree take him to a vet right away!
If the swelling is minor, just watch the animal to be sure your pet is not having breathing or swallowing difficulties. If the swelling gets huge within five or ten minutes, see a vet immediately. It is always better to be safe than sorry.
Benadryl can make all the difference.
The venom of the bee contains a number of toxic proteins, which attack various body systems. Reactions range from local swelling and pain around the stung area to anaphylactic shock with total system collapse and death. These reactions may develop within minutes of the sting, and probably will occur if the reaction is allergic in nature.
Even if the dog escapes the allergic threat of the toxins, it still faces the toxic threat of the venom. There may be damage to the liver, kidneys, nervous system or blood cells. These effects may be seen immediately or they may not be apparent for several days. Complete destruction of the dog's red blood cells may occur despite all efforts at treatment.
Please let me know how he his.
Your dog is in my prayers.