Propolis... AKA 'bee glue'. This is a resin-like material produced by the bees (from substances collected from plants in the wild).
 
The bees can use this substance to mend, repair, and strengthen their hives.  Propolis is thought to have antibacterial, antiviral, antifungal, and antioxidant and anti-inflammatory properties. Propolis may promote healing on skin injuries or inflammation.