Potamanthus luteus (Linnaeus, 1767) is the only representative of the Potamanthidae family in Europe, with an explosive growth rate in terms of numerical presence and mass increase in springtime. Aim of this study was to analyse the growth rate and the feeding habits of P. luteus nymphs in the Bormida river (NW Italy). In particular, we investigated the growth pattern of three populations, located in stations with different altitude. Thermal regimes of the three stations where assesses by using HoBo WaterPro Datalogger. Immature stages of P. luteus were collected from the time they appeared (March 2006) until their emergence as adults (June 2006). In total, 1407 nymphs of P. luteus were collected and measured. Results showed that temperature explained most of the variation among nymphs growth rates in the three stations: nymphs of the lowest station developed faster and emerged before than nymphs of the upper stations. The diet of the nymphs in the three stations was similar, and it was based mainly on fine detritus. We suppose that higher temperatures would strongly influence bioenergetics and development, and play a main role in fostering faster growth in the downstream population of this mayfly.