“Brtva” is the indentation of a rock, over-looking towards east or south, which is closed with a frontal lid and stuck with mud or cowpat. There is a small gap which allows the bees to find their place in the new habitat.
Swarm is a new bee community which separates from its old company, i.e., the swarming is a natural process for reproduction of the bee groups. After they separate from the old group, the swarm of bees inhabit another location, i.e., they form a new habitat in some cavity of a rock or tree.
It is not known when exactly the cunning Mariovo people realized that they can trick the bees in this way, yet it is known that the Mariovo honey was a well-known and demanded product during the Ottoman Empire.