 Some wasp lineages (e.g.Crabronidae) show variation, with some species practicing mass provisioning, while related species may bring back prey after the egg has hatched, and then seal the nest (such "delayed provisioning" is considered to be a stage in the evolution of progressive provisioning and thus of parental care in insects), or re-open the nest and add more prey items as the larva grows, which is genuine progressive provisioning.In 1958, Howard E. Evans published a study of the nesting behaviour of Sphecini digger wasps, showing a range of ways of stocking their nests.