I have made a ton of "corn warmers." I use whole kernel dried corn and buy it at our local gardening store. I store these warmers on a closet shelf. We have one for each family member and then a few extra. Made them for a ton of relatives.(the school secretary uses it to warm up her bed in the winter.) We do not have a problem with bugs or critters in the house, so can't answer if a critter would be attracted to them.
I can give you directions if you would like,, just PM me.