Robins will take seeds (eg sunflower hearts) but they are insect/grub eaters.
If you have any robins nearby then I agree with the idea of digging in the garden. They will spot you and be down to see what bugs etc you have exposed.
I've not tried maggots but the robins around here will do almost anything for live mealworms - we had one that would take a meal worm or two from a pot on the window sill then fly in through the kitchen window and out the back door.
In our garden it has to be live ones, the dried ones are ignored, though I have heard other people have had success.
An advantage of mealworms over maggots is that if they escape being eaten they develop into innocuous beetles rather than bluebottles, but a disadvantage is mealworms are not cheap.
Mealworms are liked by many birds - great tits, blue tits, blackbirds, great spotted woodpeckers, and, a little unfortunately, magpies. Superb birds to see but the mealworms will go in one sitting.
Dave