For the past 10 years I have been adding iodized table salt to the
     spring TM dust mixture and pollen substitute fed to hives in
     March-April.  The reason has nothing to do with what I was taught,
     read or science.  Rather, the "logic" pertained to nuisance complaints
     I have received over the years from the public regarding honey bee
     behavior and perceived agressive behavior.
 
     The specific complaint that got me thinking was called to my office
     from my home town.  The individual had returned home from a fishing
     trip and hung out the rugs from the boat to dry.  He had been fishing
     in the Atlantic.  He claimed that bees were covering his boat carpets
     by the 10's of thousands  in search of water.  I soon realized that
     these had to be my bees from my home apiary of 12 hives across the
     stream & woods from his place(1/4 mile).  The stream never goes dry
     and ranges from 1-2 feet deep to whitewater.  I know that the bees get
     water there from the banks of wet sand.  I made an official
     investigation not letting on that I knew the beekeeper quite well.
     He was correct in his estimate on the number of bees.  They covered
     the rugs like a bee beard.  However, the rugs had been long dry and
     the bees were gathering the sea salt....hmmm.
 
     Additional evidence of bees' need for salt have arisen from nuisance
     complaints regarding animal feces.  A couple years back a rabbit farm
     called concerning "millions" of bees working piles of rabbit manure
     that had been piled up.  I have had calls from both chicken farmers
     and beekeepers regarding the bees on chicken manure piles.  Two Maine
     beekeepers claim that the bees stopped rearing brood after working the
     chicken manure.  One theory we came up with, but was never proven
     pertained to Larvadex which is a systemic fed to poultry to control
     flies (IGR for the maggots).  The most recent complaint was this past
     August where a kennel owner complained that bees were all over the dog
     feces at his kennel.  His concern was that the husky sled dogs were
     snapping at the bees and he didn't want to loose any of the valuable
     dogs.  I suggested that he hose out the kennel which he would not do
     since they were dirt not concrete.  I put the dog guy in contact with
     the keeper and suggested that they provide either moist cow licks or
     canning salt near the kennel to train the bees away from the dogs.  I
     recommended that if the bees wouldn't leave the feces to try adding a
     little sugar or honey to the salt to entice them away.  The guy
     stopped complaining after working with the keeper.  I don't know if
     they were successful in getting the bees out of the kennel, but no
     news is good news from where I sit.
 
     To make a long story longer, bee behavior indicates that they need
     salt and/or minerals at certain times.  My experience suggests that it
     is during spring buildup and during hot spells.  I have also noticed
     butterflies workinng bear and coyote droppings.  Enough bull for now.