Bees can sometimes establish hives inside wall cavities which requires treatment quickly as some people are highly allergic to bee stings.
Treatment to the wall cavity will eliminate the bees, however, the temperature of any honey they form is regulated by the bees. Once the bees are dead, the honey (if the hive has been active for a long period of time) will run down the inside of the wall cavity possibly creating a problem by attracting cockroaches and ants.