Strikingly beautiful Resin plugs are made from plant resins, saps or pitch. They can be clear, white or yellow. They often remain sticky, but can dry out to be crusty. They often smell like pine or fir. Sometimes they are made exclusively of clear resin.
Often they contain bits of imbedded debris.
Resin is used for nest plugs by a variety of bees (Dianthidium sp., Heriades sp. and occasionally, some Megachile sp.) and wasps (Passaloecus sp.).