But the species has spread spectacularly over the last half century. Dates of first recorded occurrences in various countries are listed in Reise et al. (2000).[7] In Europe, Boettgerilla pallens was first found in 1949 (in Germany).[8] It has now become naturalized in most of Europe although it has conspicuously not been reported from most of Spain, Italy and the Balkan Peninsula.[7][9] Countries where it occurs include:
Boettgerilla pallens is very narrow and slender slug, almost worm-like and sharply keeled.[10] The color is pale greyish or with bluish hue.[10] The head and keel is slightly darker.[10] The mantle is pointed at its posterior end and equipped with fine concentrical grooves.[10] Sole is pale yellow.[10] Mucus is colourless.[10] Juveniles are yellowish to dirty white.[10]
The body length is up to 60 mm.[10] The width is up to 3 mm.[10]
The shell is small, fragile, 1.5–3 x 0.8–1.5 mm, with median nucleus and growth lines, denser in the posterior part, no thin margin, located below the very terminal section of the pointed end of the mantle.[10]
Reproductive system: Penis is elongate and broader than vagina, epiphallus and spermatheca.[10] Epiphallus is swollen and connected to penis laterally near its posterior end, by a long thin duct, which is thinner than vas deferens.[10] Vagina as long as penis and almost as narrow as vas deferens.[10] There are no accessory glands.[10] The spermatheca is elongate and relatively short.[10]
Boettgerilla pallens is much more slender than Milax gagates. The sole is more slender.[10] In Milax gagates the posterior end of the mantle is rounded, its shell is larger and better visible, its colour more yellowish-brownish.[10]
Ecology
Reise et al. (2000)[7] review aspects of the distribution, mode of range expansion, and other aspects of its ecology.
Boettgerilla pallens inhabits a very wide range of habitats, including gardens, grassland, coniferous and deciduous woodland, and is tolerant of a wide range of soil pH, calcium content and water content.[7][32] It lives at altitudes of up to 1750 m in the Caucasus[3] and in Switzerland at up to 1600 m, but usually below 700 m.[14] It can be considered as synanthropic,[3] although it is now often found also in undisturbed habitats.[7]
Although it may often been found under logs and stones, it is predominantly subterranean, adapted to moving through earthworm burrows and similar spaces in soil, 2–20 cm (maximum up to 60 cm) below surface.[33] Snails move rapidly away from bright light sources.[33]
Feeding is seldom intensive: slugs usually take a few bites (of earthworm faeces, detritus etc., also arionid eggs) and move on.[33][34] Although often found in gardens and greenhouses,[32] it has only rarely been considered a pest.[35] One study reports it coming to the surface at night to predate snails.[36]
Mating and egg-laying is during late summer and into autumn in Britain (October in Germany).[33] Eggs are laid 9–27 cm below the surface as several clutches of 1–6 eggs .[33] Adults survive egg-laying but die shortly afterwards.[33] Juveniles hatch after 20–22 days at 17 °C (in Germany),[34] between October and December (in Britain).[33] Juveniles turn colour from white to grey in May–June.[33]
References
This article incorporates public domain text from the reference.[10]
^ ab(in German)Simroth H. (1912). "Neue Beiträge zur Kenntnis der kaukasischen Nacktschneckenfauna". St. Petersburg (Russia), 1-140. 10 Plates. 55-58. Table 3, figure 50, table 8, figure 32.
^ abWiktor A. (1959). "Boettgerilla vermiformis n. sp. (Mollusca, Pulmonata)". Communication of the Poznań Society of Friends of Science, Department of Mathematical and Natural Sciences, 4.
^ abcdefgh(in Polish) Wiktor A. (1989). Limacoidea et Zonitoidea nuda. Slimaki pomrowioksztaltne (Gastropoda: Stylommatophora). Fauna Poloniae 12, Polska Akademia Nauk, Warszawa, 208 pp., page 137-139.
^ abcdefgKantor Yu I., Vinarski M. V., Schileyko A. A. & Sysoev A. V.(published online on December 22, 2009). "Catalogue of the continental mollusks of Russia and adjacent territories". Version 2.3.Archived 2018-12-22 at the Wayback Machine
^Colville, B.; Lloyd-Evans, L.; Norris, A. (1974). "Boettgerilla pallens Simroth, a new British species". Journal of Conchology. 28 (4): 203–208.
^ abSchmid, G. (1969). "Boettgerilla vermiformis auch in Frankreich und Belgien". Mitteilungen der Deutschen Malakozoologischen Gesellschaft. 2: 20–21.
^(in German) Schmid G. (1962). "Boettgerilla vermiformis Wiktor, 1959, eine neue Nacktschnecke in Deutschland (Gastropoda, Parmacellidae)". Archiv für Molluskenkunde91: 105-108.
^ abTurner, H.; et al. (1998). Fauna Helvetica 2: Atlas der Mollusken der Schweiz und Liechtensteins. Terreaux, Neuchatel: Centre suisse de catographie de la faune.
^(in Czech) Hudec V. & Mácha S. (1961). "Pozoruhodný plž z rodu Boettgerilla Simr. na Ostravsku - nový druh pro ČSSR". Přirodovědecký Časopis Slezký22: 303-310.
^Valovirta, I.; Nikkinen, A. (1970). "Boettgerilla vermiformis Wiktor (Gastropoda, Parmacellidae) found in Finland". Annales Zoologici Fennici. 7: 188–190.
^(in Lithuanian) Šatkauskienė I. (2001). "Naujos šliužu rušies Lietuvoje - Boettgerilla pallens ir retuju Lietuvos sausumos moliusku rušiu apžvalga" [A REVIEW OF RARE LITHUANIAN TERRESTRIAL MALACOFAUNA SPECIES AND THE BOETTGERILLA PALLENS SPECIES NEW TO LITHUANIA]. Ekologija (Vilnius) 2: 56-60. PDF.
^Borredà, V.; Martiní-Ortí, A.; Nicolau, J. (2010). Guia de camp dels Mol·luscs d'Andorra. Andorra: Centre d’Estudis de la Neu i de la Muntanya d’Andorra. ISBN9788497799577.
^Vaupotič, M.; Velkovrh, F. (1997). "Contribution to the knowledge of the molluscan fauna (Mollusca) in northe¬astern Slovenia" [Contribution to the knowledge of the molluscan fauna (Mollusca) in northeastern Slovenia]. Acta Biologica Slovenica. 41 (1): 37–45.
^Wiktor, A. (1994). "Contribution to the knowledge of the slugs of Turkey (Gastropoda terrestria nuda)". Archiv für Molluskenkunde. 123 (1–6): 1–47. doi:10.1127/arch.moll/123/1994/1.
^Margry, C.J.P.J. (2014). "First record of Boettgerilla pallens Simroth, 1912 (Gastropoda, Pulmonata, Boettgerillidae) on the Canary Islands". Basteria. 78 (4–6): 57.
^Mc Donnell, R.J.; et al. (2014). "First report of the invasive slug Boettgerilla pallens Simroth, 1912 (Boettgerillidae) in the United States". American Malacological Bulletin. 32 (2): 209–210. doi:10.4003/006.032.0210. S2CID86035194.
^Mc Donnell, R.J.; Vlach, J.J.; Reich, I.; Colton, A.J. (2020). "Boettgerilla pallens Simroth, 1912 (Boettgerillidae): A new invasive slug species in Oregon, U.S.A.". American Malacological Bulletin. 38: 63–65. doi:10.4003/006.038.0106. S2CID220837068.
^Araiza-Gómez, V.; Ruiz, E.A.; Naranjo-García, E.; Zúñiga, G. (2015). "Recent collecting reveals the presence of Boettgerilla pallens (Stylommatophora, Boettgerillidae) in Mexico". American Malacological Bulletin. 33 (2): 1–5. doi:10.4003/006.033.0215. S2CID87393631.
^ abDe Wilde, J.J.; Van Goethem, J.L.; Marquet, R. (1983). "Over de verspreiding, de uitbreiding en de oecologie van Boettgerilla pallens Simroth, 1912 in Belgie". Studiedocumenten van het K.B.I.N., Brussel. 12: 1–31.
^ abcdefghGunn, A. (1992). "The ecology of the introduced slug Boettgerilla pallens (Simroth) in North Wales". Journal of Molluscan Studies. 58 (4): 449–453. doi:10.1093/mollus/58.4.449.
^ abDaxl, R. (1967). "Ein Beitrag zur Biologie von Boettgerilla vermiformis Wiktor 1959". Zeitschrift für angewandte Zoologie. 54: 227–231.
^Moolenbeek, R.G. (2002). "Schade door Boettgerilla pallens Simroth, 1912 aan gewassen". Spirula. 326: 56.