Deep beneath the surface of some of Europe’s most celebrated subalpine lakes, an invasion has been unfolding largely out of sight. Now, for the first time, scientists have pulled together the full picture in a single, openly accessible database. A research team led by Angela Boggero and colleagues has published 367 georeferenced occurrence records of invasive crayfish collected from 17 lakes across Piedmont and Lombardy in north-western Italy, documenting sightings from 2017 through 2025. The database, released in the Biodiversity Data Journal, compiles four separate datasets in the standardised Darwin Core Archive format and is freely available through the Global Biodiversity Information Facility (GBIF), transforming scattered field notes into a powerful, reusable resource for ecologists, water managers and anyone concerned about the health of freshwater ecosystems.
The three species at the heart of the database all hail from North America, and all three are among the most damaging aquatic invaders Europe has ever faced. Faxonius limosus, the spiny-cheek crayfish, originates from the Atlantic watershed of North America. Pacifastacus leniusculus, the signal crayfish, comes from the north-western United States. Procambarus clarkii, the red swamp crayfish, is native to the southern United States and north-eastern Mexico. Together they drive biodiversity loss, restructure food webs and undermine the ecosystem services that lakes provide, from clean water to fisheries. Several introduced crayfish species are listed as species of Union Concern under EU Regulation 1143/2014, a designation that reflects their severe ecological and economic toll and obliges member states to manage their spread.
Freshwater ecosystems are exceptionally vulnerable to human-mediated species introductions, and invasive crayfish rank among the worst offenders on the continent. Yet scientists have long struggled with fragmented and incomplete spatial data, which makes it fiendishly difficult to assess the true costs of these invasions. Significant gaps persist in reporting the economic damage caused by crayfish worldwide, and the absence of comprehensive records hampers both research and the design of effective management strategies. By mobilising FAIR data — a term meaning Findable, Accessible, Interoperable and Reusable — the new database directly addresses that deficiency, allowing long-term analyses of invasion dynamics that were previously impossible at a regional scale.
The study area spans an impressive gradient of lake types, from large, deep glacial basins such as Lake Maggiore to small, shallow waterbodies of fluvial and tectonic origin scattered across the Piedmont plain. Two of the study lakes, Maggiore and Orta, belong to the national Long-Term Ecological Research network known as LTER Italy, meaning they are monitored continuously as sentinels of environmental change. The remaining lakes carry conservation designations: they are registered as Special Areas of Conservation, Special Protection Areas, or components of the European Union’s Natura 2000 network under the Birds Directive. That such heavily protected waters harbour thriving populations of North American crayfish underscores how thoroughly these invaders have penetrated even the continent’s most safeguarded habitats.
The fieldwork behind the database combined standardised trapping with meticulous taxonomic verification. Sampling sites were chosen where sediment type and vegetation cover offered suitable crayfish habitat, and where the animals had been confirmed or suspected previously. The number of sites per lake was scaled to surface area, with four stations in Lake Mergozzo and six in Lake Orta. At each site, 13 interconnected traps, spaced two to three metres apart, were deployed on the shallow lake bottom overnight for roughly 12 hours, coinciding with peak crayfish activity. Each cylindrical trap, measuring 30 by 60 centimetres with a one-square-centimetre mesh, was baited with 20 grams of cat food — an unconventional but effective lure. The catch per unit effort, calculated as total catch divided by the number of traps multiplied by nights, provided a comparable abundance index across lakes and years.
Quality control was equally rigorous. Geographic coordinates were verified using Google Maps, and every specimen was identified to species level by taxonomic experts using standard identification keys, with molecular analyses performed whenever a doubtful case demanded certainty. This precision matters, because the three invaders can be confused with one another, and because Faxonius limosus was itself reclassified taxonomically, having formerly been known as Orconectes limosus following a major revision of crayfish nomenclature in 2017. All native species caught incidentally in the traps were immediately released unharmed, ensuring the monitoring programme did not itself become a further disturbance to the lakes’ fragile ecological balance.
The data reveal striking patterns in how the invaders partition the lakes. In Lake Maggiore, 80 occurrence records from 75 sampling points collected between April 2017 and July 2018 captured all three species, but Faxonius limosus dominated, particularly in May, achieving a mean catch per unit effort of 1.14. In Lake Orta, monthly sampling from June 2021 to May 2022 generated 186 records and documented something ecologically remarkable: the coexistence of F. limosus and Procambarus clarkii, with the red swamp crayfish accounting for more than 80 percent of total abundance from May to December. Lake Mergozzo, by contrast, hosted only F. limosus, whose abundance peaked between June and October 2021 before thinning to occasional records by the following spring.
The seasonal signature in the data is unmistakable. Both F. limosus and P. clarkii reached peak densities in the summer and autumn months, and the pronounced summer predominance of the red swamp crayfish reinforces its reputation as a warm-water invader, flourishing as lake temperatures climb. Pacifastacus leniusculus, meanwhile, made a far more restricted appearance: it was recorded only once, in July 2018, in the northernmost part of Lake Maggiore on Swiss territory. The most recent dataset, gathered between June and October 2025 across all 17 lakes, recorded presence or absence in each waterbody and found crayfish absent in seven of them. Intriguingly, that survey also documented P. clarkii for the first time in Lakes Pistono, San Michele and Sirio, extending the known invasion frontier, while mean abundance of the red swamp crayfish varied from more than 1.5 individuals per unit effort in Candia and Pistono down to less than 0.5 in five other lakes.
Some of the findings hint at shifting dynamics that will repay close monitoring. Catch rates of Faxonius limosus in Lakes Orta and Maggiore during 2025 fell well below those recorded in 2021 and 2022, and the mean catch per unit effort of both species in Lake Orta was significantly altered in 2025 compared with the earlier survey. Researchers hypothesise that the occurrence of non-native crayfish across the region is shaped by hydrological connectivity between waterbodies, predator-prey interactions, and even illegal human activities, such as unauthorised introductions. A further curiosity emerged from Lake Orta, where scientists reported a new morphotype of Procambarus clarkii bearing atypical marbled colouration remarkably similar to the marbled crayfish P. virginalis, a species famous for its ability to reproduce without males.
The database is far more than an archival exercise. Because each of the four datasets carries its own Digital Object Identifier and is published under an open licence, the records can be linked to global invasive species registers, including those maintained by the Invasive Species Specialist Group and the Global Register of Introduced and Invasive Species. The data have already fed into several peer-reviewed studies on crayfish biometry, habitat preferences and invasion history, and they now provide an evidence base for regional management strategies in Piedmont and Lombardy. As invasions accelerate across freshwater systems worldwide, this first consolidated picture of three North American crayfish in 17 Italian lakes offers both a warning and a template: rigorous, standardised, openly shared data is the indispensable foundation for defending vulnerable aquatic ecosystems before the invaders dig in for good.
Subject of Research: Occurrence and distribution of three invasive North American crayfish species in lakes of north-western Italy
Article Title: First database of invasive crayfish in north-western Italian lakes
Article References: Kamburska, L., Zaupa, S., Orlandi, M., Garzoli, L., & Boggero, A. (2026). First database of invasive crayfish in north-western Italian lakes. Biodiversity Data Journal, 14, Article e189983. https://doi.org/10.3897/bdj.14.e189983
Image Credits: AI Generated
Keywords: invasive crayfish, Faxonius limosus, Pacifastacus leniusculus, Procambarus clarkii, GBIF, freshwater ecosystems, Piedmont, Lombardy, Lake Maggiore, biodiversity data, Darwin Core Archive, Natura 2000
News Source: Margaret Porter. (October 19, 2026). Invasive Crayfish Map: First Open Database Tracks Three North American Invaders Across 17 Italian Lakes. Scienmag.
