Greek Mythology:
In Greek mythology, the caduceus is the staff carried by Hermes, the messenger of the gods, as a symbol of peace. It was also carried by other heralds, such as Iris, the messenger of Hera. The caduceus was originally a rod or olive branch with two shoots, garlands, or ribbons. Later, the garlands were interpreted as two snakes entwined in opposite directions with their heads facing, and wings were added to the staff above the snakes to symbolize Hermes' speed. The caduceus was also a badge of diplomatic ambassadors and was associated with commerce, eloquence, alchemy, thievery, and lying.
 
Medical Symbol:
The caduceus is the official insignia of the United States Medical Corps, Navy Pharmacy Division, and the Public Health Service. It probably first appeared as a medical emblem in the 16th century, when it was applied to the chevrons of U.S. Army hospital stewards. The caduceus' use as a medical symbol may be ironic, as destructive creatures are used to represent a healing purpose.