A long-term diet analysis of a polyphagous jumping spider Yllenus arenarius Menge 1868 (13 yr, n  =  321 prey items) was carried out in Central Poland. Due to the spider's long life cycle two cohorts are present for the whole season and for one month three cohorts coexist, which allowed me to investigate whether coexisting spiders feed on similar or different prey. Diets of spiders from these three cohorts were found to differ in three aspects: prey taxa, prey diversity and prey size. Spiders from each cohort maintained a fairly constant ratio between prey size and their own size throughout the life cycle, which resulted in dietary separation between individuals from coexisting cohorts. Such mechanisms may reduce the intensity of competitive interactions between coexisting spiders.