Folia Historico-Naturalia Musei Matraensis - A Mátra Múzeum Természetrajzi Közleményei 10. (1985)
De Wilde, J. J. — Van Goethem, J. L. — Marquet, R.: The distribution of the species of the genus Deroceras Rafinesque, 1820 in Belgium (Gastropoda, Pulmonata, Agriolimacidae)
Figs 50-52 show the effectiveness of the survey carried out during eleven years. Before 1972, relatively few localities close to human habitats were sampled. During this survey, collections were also made in numerous gardens, fallows, etc. All landsnail records in Belgium, December 1982 All records of D. laeve, December 1982 The result is a maximal cover of D. reticulatum with respect to the total number of sampled U T M squares /fig. 50/. The results for P. laeve, found in 55% of the sampled U T M squares /fig. 51/ appear to be more realistic than the 19% obtained pre 1972 /fig. 3/. It seems even possible to us that D. laeve could be found in nearly all the 375 U T M squares, as is certainly the case for D. reticulatum, but it would be more difficult and time-consuming to prove it. Indeed, D. laeve prefers very damp places and consequently is more limited within the individual U T M squares than is D. reticulatum. For comments on the distribution of D. caruanae , see further. D. agreste was recorded for the first time in Belgium i'n 1972 : Dinant, 3 specimens, leg. M. LAMBIOTTE; Gochenée, 1 specimen, leg. W.N. NEUTEBOOM /see J. VAN GOETHÉM, 1974/. So far only 13 records are known from the period 1972-76 /fig. 53/. It is curious that this species was not found in 1979 or 1980 /see figs 33,37/. However, we still believe that D. agreste could be autochthonous in Belgium. The authors will revisit the sampled sites of. D. agreste in order to check if the populations found in 1972-76, still exist. DISPERSAL OF DEROCERAS CARUANAE D. caruanae was originally described from Malta /in 1891/, and subsequently only found in the Mediterranean region. We feel that its original home must be situated there. As mentioned before, D. caruanae was found for the first time in Belgium in 1968 /see J. VAN GOETHÉM, 1974/. It was not collected again during the period from 1969-1971. But from 1972 the number of records increased very rapidly, showing an explosive dispersal of this slug. A series of cumulative maps /figs 54-65/ clearly shows this phenomenon. All records of D. reticulatum, December 1982 All records of D. caruanae, December 1982 111
