The discarded paper nests of Polistes wasps make excellent nesting places for other species of aculeate Hymenoptera, especially for those species that work in mud. I have already published accounts of such use of the nests by the wasp, Trypoxylon clavatum and the bee, Osmia lignaria. Both of these species clean out old Polistes cells and use them for their own young. With mud they partition the cell into small rooms, provide each with food and an egg, and finally seal the opening with a plug of mud.