My hummers have been ticked-off recently because carpenter ants
are taking over the feeder. I put fresh out last evening & this morning
the feeder was full of ants, drowned & alive.
I've put vegetable oil, then orange oil, & then DE on the chain holding the feeder, but they march right over them all.
Any suggestions? Thanks.

I put Vaseline on the chain that my feeders hang on. The ants wont cross that.

I saw one of these 'ant moats' this weekend. My friend said it works well...

http://www.thebackyardbirdstore.com/main/product.asp?productID=362

Thanks so much for all the advice!
Happy (hot) gardening!