Well it could be rats , mice or squirrels but birds have been spotted eating the cobs on our site. Magpies, crows and blackbirds love them and we have lots of them as well as wood pigeons. They remove the top of the husks and work the way down eating the corn just as we would. Whatever it is eating them the husk on Extra Tender & Sweet is difficult for them to get at. Apparently birds taking sweetcorn is a big problem in the USA and they have bred sweetcorn that has tight husks that are difficult for them to remove. However the USA varieties probably won't do as well in our climate.