Nesting is a common behavior among animals, with the purpose of protecting and providing food to the young. While many bees and wasps build their nests underground, some species use hollow stems or holes in trees. They often take over holes made in the past by beetles and other insects, but some bee species, such as carpenter bees, make their own holes using their powerful jaws.
Once these holes are found or made, the nests are changed using a wide selection of materials such as mud, dirt, resin, pebbles, silk, and many types of vegetation. Each nest is provided with a mixture of pollen, nectar, and saliva (or a prey species in the case of wasps) before the eggs are laid.
Each egg is laid in its own individual cell, or room, along with all the food required to develop from a larvae into an adult.These brood cells are lined up end-to-end in a row and sealed off with nesting materials that are highly specialized to an individual species.
Because the nesting materials are so distinctive to a particular species, researchers are able to identify the type of bee based completely by which materials are used to seal off the nest holes.
Source: Moissett, Beatriz and Buchmann, Stephen. Bee Basics: An Introduction to Our Native Bees. A USDA Forest Service and Pollinator Partnership Publication, 2010.