Scientists are continually learning more about the mechanics of a butterfly’s proboscis. Initially thought to work only as a suction type of device, it is now known to work more like a straw that is lined on the inside with paper towel. Liquid works its way up the proboscis on the inside of it, but not as a solid line of fluid, like when we drink through a straw. More air than water works up the center of the proboscis. Check out the link below to read a paper on a study on Monarch proboscises.
Butterfly Fun Facts 