Certain invasive exotic species, such as the red swamp crayfish, are harmful to our environment because they nibble on aquatic plants, dig burrows in banks, and transmit crayfish plague to native species. "But there are also non-native fish and crayfish that are not harmful and do not need to be controlled," ecologist Pim Lemmers argues in his Ph.D. thesis, which he will defend at Radboud University on 30 May.
