Hexamerins are the most abundant proteins in the haemolymph of honey bee (Apis mellifera) larvae and pupae. They serve as an aminoacid source for development of pupa, when a bee doesn’t consume food. Furthermore, there has been an evidence that hexamerins act as juvenile hormone binding proteins. The details of this interaction, however, remained unknown. We have solved a crystal structure of a native hexamerin 70b, isolated from bee pupae, to 2.0 Å resolution. It shows that hexamerin is composed of six identical subunits, each possessing an enclosed hydrophobic cavity occupied by one molecule of putative juvenile hormone. We propose that the juvenile hormone is released upon proteolytic digestion of hexamerin. Therefore, the consumption of hexamerin is linked to level of free juvenile hormone in haemolymph, affecting the development of pupa. This mechanism might be conserved among holometabolous insects.