Detailed life cycle information is lacking for Wisconsin terrestrial isopod crustaceans. We measured head-widths of a local population of Porcellio spinicornis and compiled data on size frequencies, sex ratio and gravidity. Females were larger and formed a majority of the population. Gravidity showed a definite seasonal pattern; percentages of gravid females ranged from zero in March and April to near 80% in late May and early June.
Jass, J., K. Zandi, and B. Klausmeier. 1991. Life cycle information from a Wisconsin poplation of Porcellio spinicoris, the dark-headed isopod. 24(2): 21-26.