Those hardy Goldfinches that stay in the northern states all winter, are seed eaters. They nest late, so that weeds and flowers have produced the seed for their babies! Am sure they would not overlook a bug or worm, if on the plants, but seeds are their natural diet. Love them and they are great Thistle seed eaters. The ones that stay at my farm all winter, love the mixed seed in my hanging feeders--coldest winters/ Here is one just a week ago....