I mean, I can understand them wanting the sugar water. But why swim into the unit rather than drink at the little hole? Does surface tension suck them in? After a few days there will be a layer of ants at the top of the jar, swimming around. Is this like the ant equivilant of drowning beer (“what a way to go…”)?
I can’t tell you why but I can help you stop carnage over at your feeder.
I had the same problem :
I should probably quote the below source but don’t know how.
"Ants don’t like the smell of peppermint. They’ll avoid anyplace that smells like it, so start inside with the places you think that they might be entering. Next, do the outside where they might be coming in.
Possibilities: peppermint flavoring (used for baking), peppermint tea, and if you have a health food store nearby-Dr. Bonner’s peppermint scented castile liquid soap.
[copyrighted text deleted-see below]
For hummingbird feeders, cover the string with vaseline to keep ants off.
One possible theory, there is a traction problem where they enter to get the sugar water and some fall in and can’t get out.
I would be surprised if any of the ants want to be stuck in there.
Try an experiment. Maybe dropping a little twig or some such in along the path that the ants would take to get to the sugar water and see if you wind up with fewer ant in it. Try to position the twig so that it would make an easy escape route… It is hard for me to guess how possible such an arrange might be without seeing the actual feeder you are using.
I can personally vouch that Petroleum Jelly (noTM) stops ants from getting into a hummingbird feeder.
Small bees still get past the bee guards though. 
KidCharlemagne, I have deleted most of your post. Quotations should be limited to a paragraph or two, especially if the matter is copyrighted. You are expected to name your source, and if it is online, a link is appreciated. It appears to be from http://www.tipztime.com/area/bugtipz/ants.html Please note the copyright notice at the bottom of the page.
bibliophage
moderator GQ