Introduction. The effectiveness of Simuliidae (Diptera. Nematocera) as indicators of stream health was tested in the urbanizing area of Rome, Central Italy. Methods. 108 sampling sites were investigated in the spring to acquire data on environmental variables and black fly species. Results and discussion. The comparison of sampling and literature data highlighted the disappearance of some species (Simulium reptans, S. vernum, S. liriense), possibly due to water pollution and land use changes. Correspondence analysis confirms altitude as the main factor influencing black fly species' distribution. However, water quality becomes predominant when considering exclusively plain sites: "ornatum" and "equinum" species groups show the greatest tolerance to chemical pollution. The high course of the Aniene river and its tributaries were sampled bimonthly, confirming the spatial- Temporal black fly successions previously observed in central Apennines. The results also indicate that S. omatum may supplant all other species in areas where the rural use is substituted by urban landscape. Conclusion. In conclusion, black flies can be considered good environmental indicators to assess ecological health of both watercourses and surrounding landscapes.

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