Good to know on the bees. Chickens rarely eat ants since they have an ammonia flavor, so I doubt it was ants either.Bees certainly not. Ants I don't know? It's definitely not a year where I've noticed an increased population in ants, but the brooder is in a location one would consider ant central, but I haven't seen any lurking around. Maybe it's because the chicks are eating them

Other than antibiotics, I don't think there is much you can do at this point other than keep him warm and comfortable, if he is awake and conscious I'd dip his beak in the water to prevent dehydration. But again, this could be something internal or even viral, something that can't be fixed.