The larval development f the spider crab Hyas araneus L. was studied in the laboratory at different constant temperatures (2,6,12, and 18 °C). Linear relationships between log temperature and log stage duration were described by means of regression equations. They were used in a simple simulation model predicting larval moulting and metamorphosis at different temperatures. The most important predictions were : (1) Settlement of H. araneus takes place mainly from late May to mid-June; (2) assuming wide annual fluctuations in the average spring temperature ( plus or minus 2 °C), a total settlement period ranging from late April to early July can be expected; (3) delay of larval development due to a decrease in temperature is stronger than the acceleration caused by an equally great increase; and (4) both delay and acceleration effects become weaker during the hatching season and from stage to stage.