First record of the calico crayfish Faxonius immunis in the Netherlands (Crustacea: Decapoda)

In April 2025, an aberrant crayfish chela was found in a floodplain of the river Rhine in the Netherlands near the German border. Based on morphology and dna, it was confirmed that it concerned a calico crayfish Faxonius immunis. Sampling using crayfish traps and dip nets in April 2025 did not yield any individuals. However, sampling using edna in October revealed that there was dna present at two out of three sampled locations, suggesting the presence of a nearby population. We expect the calico crayfish to establish in the Netherlands, and expand in the floodplains of the river Rhine and interconnected waterways. Biodiversity and socio-economic impacts can be expected since this crayfish can establish high densities and is a good burrower.