Statistically significant differences were found in development duration of Hyas araneus L. larvae hatching on different days from the same egg batch. Larvae from different females show a decreasing trend in development time the later they hatch during the season. This trend was found in all larval instars; it was particularly apparent in the megalopa. Development durations in the 2 zoeal stages are positively correlated with each other, i.e. individuals developing slower than the average in the first larval instar tend to delay moulting also in the second instar. There are negative correlations between larval development time in all stages and the size of juvenile crabs, i.e. weak individuals tend to develop more slowly and to become smaller juveniles than the average. These larvae show lower accumulation rates of biomass already during the first zoeal stage. Larval development rates (at 12 °C) were not clearly affected by the temperature prevailing during previous embryonic development, but embryos incubated at higher temperatures tended to become smaller crabs.