I don't know if the ban has worked or not but I'm sure it has slowed the spread. Elimination of an invasive species, once it has become established, has generally been a losing game. One of my favorite examples is the Russian thistle (known in Russia as the "wind witch", and here as the tumbleweed). Introduced with wheat brought from the Ukraine by immigrant farmers in the nineteenth century, its range is so universal in the prairie west that few people today realize it is a highly-invasive non-native. The Kiwis may get back at us with a nasty little export of their own, the very invasive New Zealand mudsnail, absent the natural controls on its spread in its native environment, these prolific little molluscs can quickly cover the bottoms of lakes and streams, smothering all of the native invertebrates that form the food base for native fish.
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