Bees are a a group of wasps that have given up the predaceous lifestyle of feeding their offspring with animal protein (e.g., mostly other arthropods), instead provisioning their nests with plant derived protein, mainly in the form of pollen. Thus bees are dependent on flowers, and this relationship has made them the most important pollinators. Like their other wasp relatives, nest building bees will excavate nests in the ground or other materials (e.g., decomposing wood) or will occupy pre-existing cavities. Nest building bees range in sociality from entirely solitary species (i.e., most bee species) to more complex levels of communalism and nest entrance sharing, to the development of castes (i.e., non-reporducing female workers and queens) with annual or perrenial colony cycles. Other bees are cleptoparasites, with females using the nests and provisions of host bees to rear their own young.