Spain's invasive Louisiana crayfish: 50 years of costly damage

The red swamp crayfish, introduced to Spain from Louisiana in 1973 and 1974, has become the world's most widespread freshwater crayfish, causing significant ecological and agricultural damage that is now too costly to fully eradicate. Genetic research reveals the invasion is more complex than assumed, with at least one additional introduction route linked to the pet trade, alongside the original releases in Spain's Guadiana basin and Guadalquivir rice fields. The species carries crayfish plague, decimating native populations, and damages rice crops and drainage systems across Europe. The crayfish meets EU criteria as a species so widespread that complete removal is no longer cost-effective, as physical elimination from all waterways would exceed the benefits. This case underscores how poorly documented introductions can have decades-long consequences, urging caution before moving species to new environments.