Differentiating between Cepaea nemoralis and Cepaea hortensis
Cepaea nemoralis, Guelph Ontario, 18.10.2021
Snails have captured my attention lately.. Well, what I means is, whatever short attention span I have has allowed for slow movements and stillness to enter the field of focus once in while, and that slowness has been facilitated a little by watching snails. This attention and interest wasn’t of my own volition, but instead came second hand through watching my students search, find, play with, name, house, and eventually say goodbye to their snail friends. I began wondering at what the draw was for them and how these ever so slow and small animals could entrance the kids for so long. In a time when I often hear complaints from other adults that the kids just want things that move quickly, have lots of lights and loud noises, and are over quickly so as to get on to the next thing, these kids were enamored with these unlikely friends, despite their quiet and ponderous ways. The fascination has been infectious and I am getting more and more curious as time goes on.
It isn’t like my curiosity has suddenly been triggered, but rather, it has grown over the past year or so. I have long marveled at snail trails, admiring the smallest trails I know of and can reliably identify, and consistently come across. I have also been learning about new snails, like the Flamed Tigersnail (Anguispira alternata) who I met while out tracking with friends in October. But this curiosity and interest tends to slide back to one or two specific species which I encounter most often. They are the commonly spotted species in my area of Southern Ontario, and both are in the Cepaea genus, Cepaea hortensis and Cepaea nemoralis. It’s kind of tricky to know if they are both of the continent or when exactly they came here, but they are here now.
There is one way to tell these two species apart and it can be tricky. Not necessarily because of the i.d. feature, but instead the timing. These two Cepaea snails can only be identified to species when they are sexually mature adults, which turns out to be about 4 years old. Four years old. That seems like forever for many of the invertebrates (or other animals) we encounter everyday. Think of the House Flies (Musca domestica) we commonly see. Adult flies live about 30 days during warm months. They sexually mature at 16 hours for males, and 24 hours for females. When it comes to the American Robin (Turdus migratorius), though a male who was once banded shortly after leaving the nest in 1962, and was found dead in 1975, a lifetime spanning 13 years, the average age is only 2 years. It takes a relatively long time for a snail to become an adult, so we may not get to i.d. them to species as quickly as we’d like.
But getting back to learning how to i.d. the adults to species, Susan J. Hewitt, a curator with INaturalist.org wrote a short article on learning how to tell the two species apart and perhaps more important principally, how to know if the snail in hand is an adult. Essentially she writes that the two snails are differentiated by the colour of the lip of the shell and to be sure we are all on the same page, the lip of the shell is basically the rim of the opening (aperture) where the snail sticks their body out of the shell.
Cepaea nemoralis, Guelph Ontario, 18.10.2021
In younger snails, this lip is not yet fully solid. It may be a little soft, even a little pliable. Not too pliable but enough that if you gently press against it with your fingers you will find that it gives a little. This is one indicator that the snail is not fully mature and we can’t differentiate the species. Another sign is that as the snail ages the lip, along with the rest of the shell, thickens and hardens. It becomes stronger and less flexible. Along with this this thickening, the lip becomes a little flared out. When you come across a snail with the lip presenting this out-turned appearance, and is comparatively harder, then you are encountering an adult. These observations may take a little practice getting to know what is softer vs harder, what is a narrower lip vs a more out-turned lip, but as you observe these plentiful species you can come to know the difference between a juvenile versus a sexually mature adult.
Now, how do we separate the species from one another? Really, it’s all about the lip again. As the snail matures they are actively building their shells from the center of the coil outwards. The lip is the point where active construction occurs. The shells of Cepaea snails, along with most other molluscs are made up of calcium carbonate, which, if you are interested in geology, is also what makes up sedimentary rocks like limestone (which is often made up of the old dead shells and bodies of creatures with parts of their bodies made of calcium carbonate). When the snail is immature the lip remains pale, sometimes white or yellow or even translucent. But as their bodies mature, the lip hardens and the takes the colour it will continue to be. With this hardening off, we can now separate the species.
Cepaea hortensis, or the White-lipped Snail adults have a white flared out lip on the aperture of the shell most of the time, and Cepaea nemoralis, the Brown-lipped Snail or Grove Snail will nearly always have the dark flared out lip. There is some wiggle room for exceptional individuals, but from what I have been reading, this is the case most of the time.
Maybe the species distinction doesn’t matter too much, or maybe it does. The science seems to be still out on how much niche overlap C. nemoralis and C. hortensis share, but since learning about how to tell them apart I have been trying to observe for more diversity of habitats.
To learn more check these out:
Longevity Records Of North American Birds. Version 2021.1
How to tell what is a Brown-lipped Snail and what is a White-lipped Snail