Oh, I am so sorry about your cat, David. My cat goes out into my garden all the time and has never eaten any caterpillars, butterflies or other bugs. She catches and plays with the geckos and used to catch mice sometimes. She is 15 so I guess she's been careful not to eat the wrong things.
My nasturtiums attract hummingbirds, but not so much the butterflies.
As to making melons sweeter, first you must make sure they are getting as much sun as possible. Second, do the plants have lots of healthy leaves? The leaves make the sugar from the sun that goes into the fruit. Third, you must not pick melons until they are fully ripe on the vine. The stem will "slip" right off at the joint with the fruit when they are ready. If you pick them too soon they will be tasteless.
