Propolis

When foraging, worker bees primarily harvest pollen and nectar, while also collecting water and plant resin necessary for the production of propolis.

[3][citation needed] Bees seal the beehive with propolis to protect the colony from the elements, such as rain and cold winter drafts.

"Typical" northern temperate propolis has roughly 50 constituents, primarily resins and vegetable balsams (50%), waxes (30%), essential oils (10%), and pollen (5%).

[16] Propolis has been used in traditional medicine, with a rating that it is "possibly effective" for treating mouth ulcers and improving blood sugar levels in people with diabetes.

[18] A tincture of propolis may be used to seal the surface of newly made violin family bridges, and may be used in the maintenance of the bores of pan flute tubes.

Propolis, produced by western honey bee (Apis mellifera)
Two bars from a top bar hive that the bees have glued together using propolis. Separating the bars will take some effort as the propolis has hardened.
Propolis on the upper bar
Propolis drops in red (units in micrometers )
Propolis in hive