Accidental Importation of Molluscs and Insects

Abstract

I OBSERVE in NATURE (vol. xi. p. 394) a rote from the Saar und Mosel Zeitung on the introduction of a mollusc into the Moselle near Tièves. Though the name of the species is not mentioned, I presume that Dreissena polymorpha is the mollusc in question, a species known to inhabit Britain since 1824, and supposed to have been introduced with timber from Eastern or Northern Europe. It is exceedingly prolific. An instance of how this species may be introduced came under my notice a few years ago. A friend showed me some shells that he had found attached to logs of wood lying on a railway truck. These proved to be alive when put into a cup of water; and if the logs in question had been deposited on the banks of the Tay within reach of the tide, as is often the case (I should have said that the truck was on a siding near Perth Harbour), we would no doubt have found Dreissena in abundance in the course of a few years. As this mollusc lives in brackish water as well as in fresh, it is no doubt in a manner similar to what I have mentioned that it has been introduced into and spread through Britain. Another shell, Planorbis dilatatus, a North American species, was found a few years ago living in a canal near Manchester, and is supposed to have been introduced with raw cotton. Recently another case of importation of living shells came under my notice. When looking at some bales of Typha from the Nile, imported into Aberdeenshire as a material for paper manufacture, I observed some shells sticking in the dry mud adhering to the roots of the Typha. On putting some of these into water they were found to be alive, though a good many months had elapsed since the Typha had been gathered. The shells appear to belong to Bythinia, but I have not yet determined the species. It is, perhaps, not very likely that if these shells had found their way into the Aberdeenshire rivers they would have survived.