Camptosomate leaf beetles share an amazing building behavior in which females wrap their eggs in plates of fecal material to form a case. The larvae remain in this case, carrying it over their backs, enlarging and elaborating it until pupation. The final instar completely seals the case and pupation takes place inside. Here we present the first fully detailed study that evaluates how this unique animal architecture affects survival across a range of humidity conditions. We first determined whether or not the sealed fecal cases of pupae limit the amount of water lost in dry conditions or gained in more humid conditions. We then evaluated the effect this case has on the survival of beetles in these environments. We found a very drastic influence on case strength that presents a trade-off between normal development and the defensive function of the case. This affect could play an important role in the evolution of case hardness as a function of local humidity regimes.