Over the years, I have observed at least two awlsnail species in my pots, distinguishable by their soft-body colouration: one yellow and the other pale light brown. In my June 2020 post, I assumed one was Subulina octona (Miniature Awlsnail), a relatively common garden snail. The yellow-bodied species has recently disappeared, probably because I discarded some pots, leaving only the pale light brown ones (Fig. 1).

Fig. 1: Awlsnail with a faint light brown body; shell height of about 5 mm.		Fig. 2: Awlsnail with a dark yellowish brown body; shell height of about 10 mm.

Recently, I found another population of awlsnails (Fig. 2) in a different pot, which made me question my earlier identification of Subulina octona. These awlsnails have much taller shells—about 10 millimetres (mm) high—compared with the roughly 5 mm shells of those in my other pots. This size difference suggests the two groups are unlikely to be the same species. The larger awlsnails also have dark yellowish-brown soft bodies.

A 2024 ZooKeys publication [1] on five awlsnail species found in Italian greenhouses reported shell heights of 12.1–16.0 mm for Subulina octona and 9.4–13.1 mm for Paropeas achatinaceum. The other three species had shell heights below 1 mm (Table 1). Paropeas achatinaceum, rare in Singapore, was rediscovered locally in 2015 after more than a century [3]. The same 2015 publication also mentioned Subulina octona and gave shell lengths of about 1 centimetre for both species. Based on the information gathered so far, the newly discovered awlsnails are likely to be Subulina octona.

For the smaller awlsnails in my pots, about 5 mm in shell height, the most likely candidate appears to be Allopeas clavulinum (Spiked Awlsnail), based on iNaturalist images. I reviewed recent publications mentioning Singapore awlsnail species and compared them with the Subulininae listed on page 65 of the 2010 preliminary checklist of Singapore snails and slugs [3]. I found 11 publications, listed in the Appendix below, that mentioned nine awlsnail species. By contrast, the 2010 checklist listed seven. The two species absent from that checklist were Striosubulina striatella and Beckianum beckianum.

I then compiled information of all nine species from iNaturalist, along with their global and Singapore observation counts accessed on 6 September (Table 2). Of the nine awlsnail species reported in Singapore, Opeas didyma was not listed on iNaturalist. It was mentioned in a 2021 publication [4] on land snails and slugs from limestone hills in Malaysia, but no image of a live specimen was included. Little online information appears to be available for this species.

Even after reviewing the available information and images, I remain uncertain about how to distinguish these awlsnail species, except perhaps by shell height and soft-body colouration. To me, they still look very similar.

References:

[1] Manganelli G, Benocci A, Barbato D, Giusti F. Five alien achatinid land snails (Gastropoda, Eupulmonata) first reported in greenhouses of Italian botanical gardens. Zookeys 2024;1208:99-132. | Read article |

[2] Tan SK, Lim KKP, Chua MAH. Terrestrial snails and slugs (Mollusca: Gastropoda) of Pulau Tekong, Singapore. Nature In Singapore 2015;8:25-30. | Read article |

[3] Tan SK, Woo HPM. A Preliminary Checklist of the Molluscs of Singapore. Raffles Museum of Biodiversity Research, National University of Singapore, 2010. | Read article |

[4] Marzuki MEB, Liew TS, Mohd-Azlan J. Land snails and slugs of Bau limestone hills, Sarawak (Malaysia, Borneo), with the descriptions of 13 new species. ZooKeys 2021;1035:1-113. | Read article |