Compost piles serve as important habitats for various insect groups, including decomposers, predators, and parasitoids. While drosophilid fruit flies play a crucial role in organic matter recycling, the variation of their abundance and diversity in composters remains poorly understood. This study examines fruit fly assemblages across three compost localities in Poland: two orchards in Dąbrowice and Nowy Dwór-Parcela, and a vegetable-fruit farm in Skierniewice. Insects, collected using sweep netting and traps, varied in abundance. Dipteran flies were the most prevalent, representing 25 families, followed by beetles, bees, and wasps. Thrips and earwigs were the least represented. With 16 species from three genera, drosophilids were the predominant group, making up 95.6% of all specimens. These included seven cosmopolitan species, namely Drosophila melanogaster, D. hydei, D. immigrans, D. buskii, D. repleta, D. simulans, and Scaptomyza pallida, and three alien species, D. suzukii, Chymomyza amoena, and D. triauraria, the latter being a new Asian species recently reported in Poland and Europe. In addition to D. suzukii, another significant pest, Carpophilus hemipterus, was also recorded in the compost piles. Most species were fruit breeders or decaying plant material inhabitants, while others were mycetophagous (D. testacea, D. transversa, D. phalerata, D. funebris) or frugivorous-fungivorous (D. subobscura). Shannon-Wiener diversity indexes ranged between 1.1 and 1.4 across three localities, with the highest drosophilid diversity found at the Skierniewice farm. Drosophila melanogaster was the most numerous fruit fly at all the examined compost piles, while the relative abundance of other species depended on the composter site. These findings emphasize composters as underexplored hotspots for drosophilids, directing further study of their ecological niches and the potential presence of pest species.