an interesting example is the case of silk caps which cover the pupal cells of the oriental hornet "vespa orientalis". firstly, the silk insulates the pupa from the air outside the cell, and secondly, it acts as a thermostatic regulator. by virtue of its thermoelectric properties, the silk stores excess daytime heat in the form of electric charge which it releases in the form of an electric current when the temperature falls resulting in heating. cooling is aided by evaporation of excess water from the pupal cells. when the ambient temperature drops, the silk absorbs moisture and restores the moisture content by spreading water through all parts of its cocoon.