''

Bull. lnst. r. Sci. nat. Belg.: Biologic 56, 137-148, 1986 Bull. K. Be lg. lnst. Nat. Wet.: Biologic 137

The distribution of the of the genus Rafinesque, 1820 in Belgium (, Pulmonata, ) *

by J.J. DE WILDE, J.L. VAN GOETHEM & R . MARQUET

Abstract After some years we hit upon the idea to compile not only locality data but also to record information Four species belonging to the genus Deroceras are known from on collecting- sites and habitats. This would further Belgium: D. reticulatwn (MOLLER, 1774) , D. laeve (MOLLER, our knowledge on the autecology of the species and 1774), D. caruanae (POLLONERA , 189 1) and D. agreste (LIN­ NAEUS, 1758). their occurrence in time. The distribution of D. reticulatum, D. laeve and D. caruanae as The object became now to study a changing fauna known at the end of 197 1 is compared with a map showing all and to detect the dynamic processes involved as for records of landsna il species in Belgium till then. A similar com­ instance introductions, decreasing populations, parison is given for the year 1982. From the period 1972-1982, changes in densities, migrations, etc. year to year maps showing all records of each of these three For this new, comprehensive project: " An exten­ Deroceras species, are compared with a corresponding map com­ piling all landsna il records of the same year. sive faunistic and ecological survey on landsnails in At present D. reticulatum, D. laeve and D. caruanae are very Belgium (1977-1982)", a grant was obtained from widespread and common. the Belgian Fund for Joint Basic R esearch. This D. caruanae was found for the first time in Belgium in 1968. As survey was made by the " Laboratorium voor A lge­ shown by means of a series of cumulati ve maps, D. caruanae mene Dierkunde" of the " Rijksuniversitair Cen­ became very rapidly widespread (1973 onwards) presenting an explosive dispersal. Undoubtedly man assisted in its introduction trum Antwerpen", directed by Prof. Dr. W .N. and in its dispersal. VERHEYEN , and by the Recent Invertebrates Sec­ D. agreste seems to be very rare in Belgium with a limited number tion of the "Koninklijk Belgisch Instituut voor of local populations in the four southern provinces. Natuurwetenschappen", directed by Dr. J. VAN GOETHEM (see J. VAN GOETHEM, 1986; R. MAR­ QUET , 1985). The aim of this paper is to describe the occurrence Introduction and distribution of each species of Deroceras in Belgium and to investigate the dynamics of their T he last survey of the Belgian non-marine molluscs distribution patterns. was given by W. ADAM (1947; 1960). As part of his contribution to the E .I.S., one of us (J. VAN GOETHEM) assisted by members of the Recent Material and methods Invertebrates Section of the K .B .I.N., started a new malacological survey in Belgium. From 1970 In total more than 12,000 specimens representing on numerous explo rations were made each year, c. 2,600 lots of Deroceras species were identified according to a program for covering the whole Bel­ and recorded on U .T.M. grid maps with 10 x 10 gian territory within the next 10 or 15 years (e.g. km2 squares. T his material comprises all Deroceras fi gs 13, 17, 21, . . . give an idea of the sampled specimens present in the collections of the Konink­ U .T.M. squares for the respective years) . lijk Belgisch Instituut voor Natuurwetenschappen (K.B.I.N.) . • T he present article has been published without the permission The total number of 10 x 10 km2 U.T.M.-squares of the authors, in Fol. Hist. -Nat. Mus. Matr., Gyiingyiis, 10 (1985): in Belgium is 375. This number includes the trape- 103- 11 4, although the authors had prepared it fo r and proposed it to Soosiana. Unfortunate ly, the printing of the maps was not Legen.ds as required and, furthe rmore , the authors did not see the galley * : Pre 1950, collected alive or observed alive. proofs. We conside r this article in the Gyiingyi:is publication to e : 1950 onwards, collected alive or observed alive. be presented in a confusing way. Therefore, we consider it appro­ • +: Records concerning one single particular year as pri ate to republish this paper in an acceptable form. indicated. ''

138 J.J. DE WILDE, J.L. VAN GOETHEM & R. MARQUET

All records of landsnails All records of D. reticulatum

I l ~q%

?

I ~ pre I 1972 ·r~

2 li b

'lJ :,!_ 1~% '

~- I 'l uw _.,. 1972

1::2 '

~ Fe 5 '!"' 6 h ] J

['_ 1\ ['_ I-- I--I'- l)_' 63% r, p

1973 11

• 1 9 ~ 10 ~ h J b J

..h 1\ 6 Lf% I'- '.11\._'-t" C>l Y\ ~ ~ ,. [f' ] ~:-= I? Mr. ,..•, ~ 1974 • ~ ill 1--- 1 13 .!- 14 ,1.-,. b, J I I

The distribution of the species of the genus Deroceras Rafinesque, 1820 in Belgium 139

All records of D. laeve Al l records of D. caruanae

~~+++,~41ft~ ~~~~++~44W. 19% 1% .v _J !l v. ~B~ ~~~~p- ~1 1- ~H~~~~~~ II ~~~ - - .._.,, Hr~~: r-- f~rr,~l~~ ~~ ~~~~~~~~ - - !?;< - - \- tTl I~ I ~ !-" - . ~I pre ~1~-~++~ti~~d\ t- 1 1 - 1972

'

11 3 4 ,h ]

6% 19%

~- "' ~ ~

1972

.:!_ P=:>< --

l1 ci 7 8 w J

.h 1"\ 1\ LL 18% 1"\ 32% 0- IL rl v- l~h 4- \----- i:LL J w Iii l./1 v ~ ""' pfs;~ I'\ 1- j?£ ~ lJ I-' - - ./ 1973 I .

f j 1 1 L1 12 ,~,-, J ~ V \'-.J...-

!L 11% Bj _~% t:[[d _ ~ - -~~ ~ 12'ilr -1¥ _Jl.< ~ -~ - ~- - ~~ - -- -~li ~D. ~ ./ I~ - h: - [\ -- ,- ~ > ' - I -- 1974 - ~ - ~-- - k ~ -' I ~~ ,L - "'" - -- , _· __j_-- - ( - -i - !.( -- 1-1 -' ' ' / I L1 l1 15 -l- ""'}; / b r ~~ / J.... 140 J.J. DE WILDE, J.L. VAN GOETHEM & R. MARQUET

All records of landsnails All records of D. reticulatum

~% ~- : 1975 - fj • l1 u 17 l 18 \l. 1-- I.IJ"'f"'KY J.-]j .b

ill 61% 12. ~ ,.,., l't G 1976 Ill I y • v [ ~ 21 ~ 22 u . -p=y;::tr o~= J

53% 1- ]7- I tt 1977 h

26 11

'11.J'-.. il 95% ~' [_1. : • b. G

I'( l1 30 lL . ·--'- bob ,b I I

The distribution of the species of the genus Deroceras Rafinesque , 1820 in Belgium 141

AJl records of D. laeve All records of D. caruanae

Jl r T -- \lT 40% 1'2_ 9% I ~ \ ! ~ v· l.o ~ h b Tl h \' D. l'> ~ ;~ D I\. ~ p~ ~ ti k I li i/!9 I r. / v {): I /ri 1975 I b- ~ I ~

~ - 4 19 ~ l1 20 bL J.-i"J

4% h 33% I I ,I' l?;b-J \ V- I' - • I ~ P- . -~ ' ' - -1- - l "l ~ Bi: \-- [:.Q - I /, !-" - 1\\- 1 - ~ - ,j- ~J - \ D _[ v =t - ¥~ v ..:rr rr --f ( ~ ' !-17 fT t'r- ~ ~ ?} \ 1976 I J>- p !iii ;~ / - 1- -\-- r ' +-

I / P. l- ~ ~i p. - h ~ ~- ·~kl ~n· ~ -~~- /"" - -· f]; ,h< ::- I 23 I ~· . f\,~ p rt~ --' ,\-, J 24 L_._.__.._ - I ~ - - Ebfr

1\ I ~ 28% h ~ 15% ./,l_ H +-"' ~ \-- -· iv Ft "" +- J7 It_ - -~ IS:_ - 1::: P ~-- ~ Pi l-1 - p ~ ;<, ~.r - F ~ D=<- ~- ~ !i' ,j ~ ~ Ali 4d tl --~~ =T i I -= ~ '- \ T\ - - t I lC-- : ' 1977 t.iil> -·

- p ~

-1- 27 28 ;bJ__ :b

28%

- ~~ - 1978

- - ~ ------17 - - - l1 31 ~- t:t 142 J.J. DE WILDE, J .L. VAN GOETHEM & R. MARQUET

All records of landsnails Al l records of D. reticulatum

l ili. 1 1 ~ 6% f-: I I f-i / • I

ptf~ ; ~ :0= : '~ '!. r'-, ~ - ~ 1979 : I 1&1 d. I :

}..:-' l1 34 \) b

nf:-K 1\ lll 72% ~-' \ ~

. ~

3 8 1 ---l

1981

1l 42 rnT+Hrl++Hri~~~r~1~n · __y b

I! 6 7%

~

I

[4 L!

46 l1 ;b.I.J I I

The distribution of the speci es of the genus Deroceras Rafinesque, 1820 in Belgium 143

All records of D. l aeve All r ecords of D. caruanae

19% " I r.-r ffi 29% 0 I• - l( /i I ;;t!~ •P ["\ :=Jf:' ~ i\ ~ ;) ' ' ' 1979

, I

35 u 36 if -l'>b ;b J

37% ?'f-11 ~ % I tL<\ - - pc ~-~~ ~-.~ - -)j_ -- P~H ~I' if< ~ ,~i-" 1): IJ. - _, \ 1980 t" ~ - !r - - ~I'> 14 - ~ -r? -1-1- - ~ I-" - -I] !L r:' ~- ["'I - I" - ~ 39 u 40 l) bl.J I'!! . -\'r -- - b - ~

h 11 29% ~ ~% 1-- ~±:1 ['- t:l L\ l/1 J J.J - r- -t]] JJ ~

1981

43 4 4 ;b.J _Db

1.1. ~~% n 36% 12..

,,_( II !..< ~~ Jl ~ "" \ p~ !$<1 "' ~~ II ·~ r~r~ ~~ 1982 I~ ~ 1:;, I~, t-'1\ lr" f) t7 ~ 19 f' IJ ~ ~ ll il l"' I ~ ~ u II r=: ~ ,1 r. 1-ti 11 /1 1Lr7 i"i l'~ ~ 17 f1ilf~ R ''lt /7 I~ !', u -~-- L j't~f ' l~ l-ll t-ll 47 D 48 ··------r-~1 I'< 1':obL1 144 J.J. DE WILDE, J .L. VAN GOETHEM & R. MARQUET zoidal partitions at 6° E , as well as the peripheral D. caruanae was recorded for the first time in Bel­ squares covering not only Belgian territory but also gium only in 1968: Brussels (Woluwe), in garden, a part of a neighbour country. 1 juvenile & 6 adult specimens, leg. J. VAN At the end of 1982, 94% of all U .T.M.-squares in GOETHEM & A . LIEYROUW (see VAN GOETHEM, Belgium were sampled. 1974). In the next three years the species was, as The percentages in the right upper corner of the far as we know, not found elsewhere in the country distribution maps indicate the number of positive (fig. 4). U.T.M.-squares for the concerned species com­ For the period 1972-1982, series of maps (figs 5-48) pared with the total number of sampled U.T.M.­ are given showing year by year all records of land­ squares for the same year. snails(= sampled U.T.M.-squares) gathered by the Recent Invertebrates Section (K.B.I.N.) and by the "Laboratorium voor Algemene Dierkunde (R.U. Results C.A.)". Comparison of the corresponding maps compiling all the records for a given species, con­ All records of landsnails before 1972 (based on the firms the widespread occurrence of D. reticulatum collections of the K.B.I.N.) are indicated on fig. 1. and D. laeve in Belgium. The percentages of the About 50% of all U .T.M.-squares had been sam­ positive U .T.M.-squares for both species vary pled at that time, most of the records covering the slightly. These variations can be explained by the period from 1935 to 1950. Figs 2-3 present the fact that year after year not always the same degree known distribution patterns pre 1972 of D. reticula­ of diversity in biotopes could be taken into account tum and D. laeve, both species being widespread by sampling landsnails. On the other hand, very in Belgium, although D. laeve is less common than dry weather conditions, during certain years might D. reticulatum. be responsible for low percentages of D. laeve (e.g.

All landsnail records in Belgium, All records of D. reticulatum, December 1982 December 1982

All records of D. laeve, All records of D. caruanae, December 1982 December 1982 The distribution of the species of the genus Deroceras Rafinesque , 1820 in Belgium 145

figs 19 , 23 ; 1976 = exceptionall y dry summer) . The result is a maxim al cover of D. reticulatum with After its first discovery in Belgium, D. caruanae respect to the total number of sampled U.T.M.­ was recorded again in 1972 in 6 different U .T.M.­ squares (fig. 50). squares (fig. 8). From then, the number of records The results for D. laeve, fo und in 55% of the sam­ increases rapidly each year. With a few exceptions pled U.T.M .-squares (fig. 51) appear to be more (1978, 1980) this species was found every year even realistic than the 19 % obtained pre 1972 (fig. 3) . more frequently than D. laeve. It seems even possible to us that D. la eve could be Although in 1978 the survey was almost exclusively found in nearly all the 375 U .T .M. -squares, as is concentrated in the four northern provinces, a per­ certainly the case for D. reticulatum, but it would centage of 28 % (fig. 32) seems lower than could be more difficult and time-consuming to prove it. be expected. However, the scarcity of D. caruanae Indeed D. laeve prefers very damp places and at that time in West Flanders and in Limburg could consequently is more limited within the individual explain this low number. U .T .M.-quares than is D. reticulatwn. The low percentage for 1980 (20% fig. 40) clearly For comments on the distribution of D. caruanae, demonstrates its low frequency in the southern part see further. of Belgium. See dispersal of D. caruanae. D. agreste was recorded for the first time in Belgium in 1972: Dinant, 3 specimens, leg. M. LAMBIOTIE; Gochenee, 1 specimen, leg. W.N. NEUTEBOOM The situation at the end of December 1982 is given (see J. VAN GOETH EM, 1974). So far only 13 re­ by figs 49-52. They are directly comparable with cords are known from the period 1972-76 (fig. 53). figs 1-4. It is curious that this species was not found in 1979 Figs 50-52 show the effectiveness of the survey car­ or 1980 (see figs 33, 37). However, we still believe ried out during eleven years. Before 1972, relatively that D. agreste could be autochthonous in Belgium . few localities close to human habitats were sam­ The authors will revisit the sampled si tes of D. pl ed. During this survey, collections were also made agreste in order to check if the populations found in numerous gardens, fallows , etc. in 1972-76, still exist.

L I

\

VI/ J / ( ~ l\ ~

1

All records of Deroceras agreste (numbers indicate the year of recording) 146 J.J. DE WILDE , J.L. VAN GOETHEM & R. MARQUET

Dispersal of Deroceras caruanae known from the period 1972-76. However, these populations could also be the result of introduc­ D. caruanae was originally described from Malta tions. Since D. agreste is not synanthropic, the (in 1891), and subsequently only found in the Medi­ species is mainly thrown on natural ways for dis­ terranean region. We feel that its original home persal. It is clear that in such a case a rapid dispersal must be situated there. is excluded. As mentioned before, D. caruanae was found for D. caruanae is definetely not autochthonous in Bel­ the first time in Belgium in 1968 (see J. VAN gium. The was introduced in Belgium shortly** GOETHEM , 1974). It was not collected again during before 1968. Most probably there have been anum­ the period from 1969-1971. But from 1972 on, the ber of subsequent introductions. From 1972 on, the number of records increased very rapidly, showing number of records increased very rapidly, showing an explosive dispersal of this slug. A series of cumu­ an explosive dispersal of this slug. Fourteen years lative maps (figs 54-65) clearly shows this pheno­ after the first record, D. caruanae became one of menon. our commonest landsnails, having been recorded in Undoubtedly, D. caruanae has been introduced in 57% of the sampled 10 x 10 km2 squares in Bel­ Belgium shortly before 1968. Most probably there gium. It is obvious that D. caru.anae is a synanthro­ have been a number of subsequent introductions. pic species in Belgium and occupies a similar niche However it would certainly be impossible to ascer­ as D. reticu.latwn. This could explain the imposing tain them. It seems obvious to us that the dispersal extension in relation with human activities. At pre­ of this slug took readily place over the whole coun­ sent D. caru.anae is more densily distributed than try, but especially in the northern part. This con­ D. laeve except in the Ardennes. trasts with the dispersal of another slug during the For detailed argumentation and conclusions, see J. same period: Boettgerilla pallens SIMROTH , 1912, DE WILDE , J. VAN GOETH EM & R . MARQUET, originally known from the Caucasus. The latter 1984a and 1984b. became especially widespread in the southern part of Belgium (see J. DE WILDE , J. VAN GOETHEM & R. MARQUET, 1986). Acknowledgements Without any doubt, man is responsible for the intro­ duction and the rapid dispersal of D. caruanae in The extensive faunistic and ecological survey on Belgium: e.g. transport of vegetables, garden landsnails in Belgium (1977-82) was granted by the plants, wood, etc. D. caruanae is highly synanthro­ Belgian Fund for Joint Basic Research. pic in Belgium. For detailed argumentation and conclusions, see J. DE WILDE, J. VAN GOETHEM & R. MARQUET, 1984a and 1984b.

Conclusion

Deroceras reticulatum and D. laeve are autoch­ thonous species in Belgium. At present they are very widespread and common, the first being pro­ bably the most common landsnail species in Bel­ gium. D. reticulatum can be found in any 10 x 10 km2 square in Belgium and generally in large numbers. Records from 94% of the sampled 10 x 10 km2 squares are at our disposal, the remaining 6% having no special significancy. The species lives in almost any kind of biotope and scarcely fails on rubbish-tips. It is a synanthropic species, to be regarded as a major pest of many crops. D. laeve has been recorded up to now in 55% of the sampled 10 x 10 km2 squares in Belgium, in a wide variety of damp or very damp biotopes. D. agreste could be autochthonous in Belgium, attaining here the westernmost edge of its actual range. The species seems to be rare in Belgium with a limited number of local populations in the ** Regarding its (apid dispe rsal from 1972 o n, it is hardly be li ev­ four southern provinces. So far, only 13 records are able that this slu g remain ed unobserved for a lo ng pe ri od . 1' · 1 11 r-:t;n' l.hi~ TTI":-J'rT[QJ ~-"11<- lj; . ; . !::: :1_-,_,f ~ ' ' ...., rt l ~ · IX =r (1) f":jf"' ,;i D 0. ,I_ 1 . ~'T V'l J, .' ., - -•--' - (f) I ,. l ll ' ·~·~ -~~- ...... , +-kt~ ~~-,_~ ;_1 I" . 1'- & j-=f--i"' -·- ".._6 . I . \l'· t: j . jt- ~ L ~~~~~ ..... (3' ,: fT( I ~~ ~ ::1 [7" '-', ,' . 4.. _.. :>;~ :•r-:• . 0 ....., s6 ~;fi-;--1, r~h.~ --if~~- 1 :f1ERlj m • Y I 57 :]: ..... - · .. - 111 f-Jn-' J:rk::- =r ~ (1) 1968-1971 Up to 1972 inclusive Up to 1973 incl us ive Up to 1974 incl usive (f) "0 (1) D. (1) (f)

,.....,0 ..... =r (1) (]Q (1) ::l t: (f) \::; ~..., 0 ~ ";:; "' Up t o 1975 inclusive Up to 1976 inclusi ve Up t o 1977 inc lu s ive Up to 1978 inclus ive ~ ~ ::::"! ::1 (1) (f) ..c t: (1)

...... 00 N 0

::1

t:J:j (1) € t: 65 3

Up to 1979 inclusive Up to 1980 inclusiv e Up to 1981 inclusive Up to 1982 inclus ive ...... +>­ DISPERSAL OF DEROCERASCAR UANAE -...) ''

148 J.J. DE WILDE, J.L. VAN GOETHEM & R. MARQUET

Cited references D E WILDE, J.J., VAN GOETHEM, J .L. & MARQUET, R ., 1986. Distribution and dispersal of Boellgerilla pallens SIMROTH , 1912 in Belgium (Gastropoda, Pulmonata, ADAM, W. , 1947. Revision des mollusques en Belgique. Boettgerillidae). - Proc. 8th Int. Malac. Congress, Buda­ I. Mollusques terrestres et dulcicoles. - Mem. Mus. r. pest (1983) : 63-68, maps 1-26. His!. nat. Belg., Bruxelles, 106 : 1-298, figs 1-4, pis 1-6, MARQUET, R., 1985. An intensive zoogeographical and maps 1-162. ecological survey of the land of Belgium: aims, methods and results (Mollusca: Gastropoda).- Annis Soc. ADAM , W., 1960. Mollusques. I. Mollusques terrestres et Be/g., 115 (2) : 165-175, figs 1-2, tabs 1-4. dulcicoles. - Patr. Ins!. r. Sci nat. Belg., Bruxelles, Faune r. zoot. de Belgique: 1-402, figs 1-163, pis 1-16, A-D. VAN GOETHEM, J .L. , 1974. Sur Ia presence en Belgique de Deroceras caruanae (POLLONERA , 1891) et de Deroce­ D E WILDE, J.J. , VAN GOETHEM, J .L. & MARQUET, R. , ras agreste (LINNAEUS , 1758) (Mollusca, Pulmonata, 1984a. Over de verspreiding in Belgie van de naaktslakken Limacidae). - Bull. lnst. Sci. nat. Belg. , 50 (2) : 1-21 , figs van het genus Deroceras RAFINESQUE, 1820 (Mollusca, 1-33, 1 pl. Gastropoda, Agriolimacidae). - Studiedocumenlen van he! VAN GOETHEM, J.L. , 1986. The E.l.S. Mapping pro­ K.B.I.N., 14: 1-50, figs 1-12, maps 1-74. gram: Belgium (partim Mollusca). - Proc. 8th Int. Malac. Congress, Budapest (1983) : 327. D E WILDE, J.J., VAN GOETHEM, J.L. & MARQUET, R. , 1984b. Sur Ia distribution en Belgique des limaces du VAN GOETHEM , J.L. & D E WILDE, J.J. , 1985. On the genre Deroceras RAFIN ESQUE , 1820 (Mollusca, G astro­ taxonomic status of Deroceras caruanae (POLLONERA , poda, Agriolimacidae). -Documents de Travail de l'l.R. 1891) (Gastropoda, Pulmonata). - Archiv fiir Mollusken­ Sc.N.B., 15: 1-50, figs 1-12, maps 1-74. kunde, 115 ( 4/6) : 305-309, 1 tab.

A uthors' addresses : J .J. D E WILDE, J.L. VAN GOETHEM R . MARQUET Koninklijk Belgisch Instituut voor Natuurwete nschappe n Rijksuniversitair Centrum A ntwe rpen Recent Inve rtebrates Section Laboratorium voor A lgeme ne D ie rkunde Vautierstraat 29 Groe ne nborgerlaan 171 1040 BRUSSEL 2020 ANTWE RPE N