Hummingbirds like nectar. So do ants. This isolates the feeder by surrounding it with water so ants can't get to it. Note that this is still in development; you can buy this and use it, but it's still in the prototyping stages!
Because I know how annoying ants are, this is being sold with no profit margin, and being offered for download so you can print it at home. I'd love to see a picture if you print it yourself!
Shapeways says the Strong and Flexible Plastic is not watertight; I find this odd. In my experience it's certainly watertight; I've been using the prototype I have for about a month now with no problems.