Purple Martin Diet

Purple martins eat insects while in flight. Martins have been known to eat mosquitoes, but they prefer larger insects. A healthy purple martin need not take food from humans. There is normally no need for a purple martin feeder.

Of course, there are exceptions, but only when things go very wrong.

• A spell of cold weather can deplete the supply of flying insects. In such conditions, martins will take crickets and meal worms supplied by humans.
• An injured adult martin can be fed crickets and meal worms.
• A baby martin can be fed crickets and meal worms.

Purple martins will not take grain from your feeder or anywhere else. They only eat insects.

I have read this.
CAUTION: Only an authorized licensed wildlife rehabilitator is legally allowed to hand-feed wild birds.
But I have not yet determined the veracity of this statement. Take a look at The Wildlife Rehabilitation Directory. Also, take a look at my page on The Law and the Purple Martin Landlord.