Abstract
The life history of Petrobius brevistylis Carpenter is described from material reared in the laboratory and captured in the field (south Devonshire). A method of identifying the first eight instars is discussed and their diagnostic morphological characters described. Fecundity and time of oviposition are considered at some length. The effects of climate on various phases of the life history are considered as well as the faunas found associated with P. brevistylis. A brief description of the life history of P. maritimus (Leach) is included.