I have to disagree with the statement that citrus peel does not kill ants.
I used to live in South Florida where there is a huge fire ant problem. We killed fire ant nests by taking FRESH citrus peel and while standing over the nest, tearing the peel into small pieces and dropping it into the nest.
We also spread FRESH grapefruit peel over the lawn and used a mower to tear it up.
Don't mix the peel with the juice - that doesn't work!
Interesting, Honeybee. It sounds like all ants cannot be treated the same. Here we have Argentine ants and they are always on my grapefruits, their own personal mealybug ranch. Of course, chopped up peels are not the same thing as an intact grapefruit, either.
Right Kelli, ants are not the same - our leaff-cutting ants chop up the citrus peel in the compost pile and cart it to their own underground compost heaps where they use it to grow the fungus they feed on. One man's poison...
We have a couple of pest control companies here that use citrus oil spray to kill and/or drive carpenter ants out of people's houses. I don't have personal experience, but they wouldn't use it if it didn't work. Our entomologist at the Extension office agrees. As it's been said above, it must depend upon the type of ant.