India, Oct. 4 -- Some of the biggest environmental problems can often start with the smallest plans. The red swamp crayfish is a good example. This North American species was introduced to Spain from Louisiana in the 1970s, and more than 50 years later, it remains a huge headache for Europe. In a 2020 study in Knowledge and Management of Aquatic Ecosystems, Francisco Oficialdegui and colleagues traced the species' complicated path across the continent. Today it is the most widely distributed freshwater crayfish in the world.

The study explains that the crayfish first came to Europe in 1973. That batch was released in the Guadiana basin in the province of Badajoz in Spain. In 1974, a second, separate introduction took place in the rice fi...