The collection and the secretion of building materials are two radically different processes: one behavioural; the other physiological. This article examines whether selection pressures operating upon these have led to quite different outcomes or whether priorities common to both have led to parallel solutions. The article also examines selection pressures peculiar to secreted materials. It explores the influence of diet on the biochemistry of the secreted material and the evolutionary consequences for social species of the allocation of the costs of secreting the building material. Conclusions in some of these areas are hindered by a lack of evidence, but this also indicates opportunities for future research. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●●, ●●–●●.