Chances are if you're asked to imagine a ruthless killer, shrimp don't come to mind. But that's exactly how ecologists characterize Dikerogammarus villosus, a species from the former Soviet Union that has invaded the Netherlands and other parts of western Europe. What's more, D. villosus is on the move, hitchhiking in the ballast water of ships, and researchers expect that it will soon take over the North American Great Lakes and the British Isles. If the results of research described Friday at the winter meeting of the British Ecological Society are any indication, this foray will have disastrous effects on the local aquatic species.

Jaimie Dick of the Queen's University of Belfast conducted a series of microcosm experiments in order to demonstrate the potential impact of D. villosus on the areas it invades. He set up three large tanks, one without shrimp, another containing the native shrimp Gammarus duebeni and the third containing D. villosus. Observations revealed that D. villosus took a far greater toll on the other species in its tank than did G. duebeni, killing and mangling large numbers of blue-tailed damselflies, water boatmen, fish leeches and water hoglice. What makes D. villosus such a lethal predator may be its mouthparts, which are much larger and more powerful than those of G. duebeni. Perhaps more worrisome than its mouth, however, is the creature's ability to tolerate changes in the temperature, salinity and even oxygen level of its aquatic environment. With such flexibility, wherever D. villosus is introduced, it will probably be able to start killing.