1. The stonefly Nemurella pictetii has a highly variable life cycle and is semi- and uni-, but also plurivoltine in different geographical areas.
2. The influence of the type of food on growth and maturation of larvae was studied in laboratory experiments. Food preference was also assessed.
3. Larvae of N. pictetii are strongly opportunistic feeders utilising a broad range of food sources. However, biofilm was preferred over detritus (conditioned leaves), green algae and animal food. The highly mobile larvae quickly found the preferred food. Larvae fed on biofilm grew and developed significantly faster than larvae fed on conditioned leaves.
4. Larval growth and maturation in experiments as well as in the field differed with available food qualities. Phases of faster growth and maturation corresponded well with maximum availability of biofilm in the field. This contributes to the interpretations of differences in life cycles in the field.