Paper produced for nest-building: hornets
The nests of Vespa hornets are made out of a paper substance produced from the mixture of saliva with wood pulp.
"The powerful mandibles of the hornet are…used to cut and chew wood to make its nest. Wood pulp is mixed with saliva and converted by the hornet into a paper substance from which an elaborate tiered nest is made which may house thousands of individuals." (Foy and Oxford Scientific Films 1982:159)
Learn more about this functional adaptation.