How to tell what is a Brown-lipped Snail and what is a White-lipped Snail

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Two very pretty and very similar-looking species of land snails in the genus Cepaea are native to most of Western Europe. And both of them are introduced in some parts of North America. These two species are: the Brown-lipped Snail, aka the Grove Snail, Cepaea nemoralis (adults almost always have a dark out-turned and thickened lip on the aperture of the shell) and the White-lipped Snail Cepaea hortensis (adults almost always have a white out-turned lip on the aperture of the shell).

Both species live in colonies. They both have a fairly large globose shell, which can be yellow, red, or any pale or mixed shade of those colors. The shell can be plain in color or banded. When the shell is banded, it can have from one to five dark bands. Those bands can be narrow, or they can be so wide that two or more bands merge together.

One important thing to know is that you cannot put a species ID on a live one of these snails, or an empty shell, unless it is adult. The ID of juveniles needs to be left at the genus level. Even dissection cannot separate the juveniles into species.

How can you tell if the snail is an adult? In snails of this genus (and in many other land-snail genera), once the snail reaches adulthood/sexual maturity, the shell stops growing any larger, and instead it grows thicker. In particular, the lip (the very edge of the opening of the shell) in adults becomes greatly strengthened, strongly reinforced, and also somewhat out-turned, a bit flared-out. So, in adults the lip of the shell is thick and strong, and it is out-turned to a certain degree.

With a lot of experience, you can tell an adult from a juvenile quite easily just by looking, but until then, before trying to ID a live Cepaea to the species level when you are in the field, there is to a way check to see if the lip is mature. If you press gently on the side of the lip and it is still soft and flexible, then the individual is a juvenile. And in general if there is no sign of thickening and no out-turned appearance to the lip, the snail is a juvenile, and you will have to leave the ID as "Cepaea".

EVEN MORE IMPORTANT: A live juvenile or subadult Cepaea snail that is active will always appear to have a white lip on the shell. But what you are seeing is usually the live mantle tissue which is wrapped over the edge of the shell, actively laying down more shell material. That is how the shell increases in size. And any brand-new shell material will also appear whitish, yellowish, or even transparent. This apparent pale lip is not an indication that the shell is mature.

If an individual snail is starting to become sexually mature, you may see that the thicker lip of the adult is partially formed. You have to look closely then, because even if the adult will end up with a dark lip on the shell, the thickening often starts out pale; the dark pigment seems to be laid down a bit later, when the construction of the thickened lip is almost finished.

Almost all of the time with adult snails it is true that an adult White-lipped Snail has a white lip on the shell, and an adult Brown-lipped Snail aka Grove Snail has a dark lip to the shell. Very rarely there are exceptions to this rule, but it is best to stick with it 99.9% of the time.

Here on iNaturalist we currently have numerous observations of Cepaea that have been misidentified, and many well-meaning people have subsequently "agreed" with those IDs, causing them to become Research Grade.

Research Grade observations are fed to the AI, our Computer Vision tool. Large numbers of misidentifications cause the AI to learn the species incorrectly, and then it offers incorrect suggestions. And that helps perpetuate the mistakes!

If anyone who reads this post would like to help me sort out some of this confusion, please drop me a line. Although many (not all) of the IDs of the Dark-lipped Snail are correct, there are still dozens of observations of "White-lipped"Cepaea which will need to have the ID adjusted to the genus level, and adding a comment with "Please see" and a link to this post.

Thanks for any help you can give in sorting this out. Not only do we need the humans to learn this correctly, but, perhaps even more importantly, we want the AI/Computer Vision to learn it correctly too.

Publicado por susanhewitt susanhewitt, 08 de agosto de 2019

Observaciones

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Caracol Moro (Cepaea nemoralis)

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susanhewitt

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Agosto 23, 2019 08:40 AM EDT

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Caracol Moro (Cepaea nemoralis)

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susanhewitt

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Agosto 23, 2019 08:42 AM EDT

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Agosto 23, 2019 08:42 AM EDT

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Caracol Moro (Cepaea nemoralis)

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Agosto 23, 2019 08:45 AM EDT

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Caracol Moro (Cepaea nemoralis)

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susanhewitt

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Agosto 23, 2019 08:46 AM EDT

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Caracol Moro (Cepaea nemoralis)

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susanhewitt

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Agosto 23, 2019 08:46 AM EDT

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Caracol Moro (Cepaea nemoralis)

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susanhewitt

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Agosto 23, 2019 08:48 AM EDT

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Caracol Moro (Cepaea nemoralis)

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susanhewitt

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Agosto 23, 2019 08:55 AM EDT

Comentarios

In order to see what an adult shell of the White-lipped Snail really looks like, please check this images in the icon picture for that species:

https://www.inaturalist.org/taxa/51039-Cepaea-hortensis

Publicado por susanhewitt hace alrededor de 2 años (Marca)

Some nice Grove Snail images are here:

https://www.inaturalist.org/taxa/48586-Cepaea-nemoralis

Publicado por susanhewitt hace alrededor de 2 años (Marca)

In the past I ID'ed juveniles to the species level here on iNat when I found them within a colony of Grove Snails, and knowing that in NYC there appear to be no White-lipped Snails at all.

However, because of the need to train the AI, I went back and ID'ed all those juveniles as just plain Cepaea.

Publicado por susanhewitt hace alrededor de 2 años (Marca)

I have done that -- I hope I did not miss any.

Publicado por susanhewitt hace alrededor de 2 años (Marca)

Great article, thank you

Publicado por fero hace casi 2 años (Marca)

That is a very helpful article! Thanks for putting the work into it. I did learn something new and will check my Cepaea observations now with this in mind :-)

Publicado por ajott hace más de 1 año (Marca)

Glad to hear that the article is helpful. :)

Publicado por susanhewitt hace 8 meses (Marca)

Great article. Thank you for sharing the knowledge.
@tastyy recommended this read to me and it's time well spent. :)
I hope to not misidentify these two anymore.

Publicado por marcinswiostek hace 4 meses (Marca)

Since we can't feel the rim, it might help to say why this flared-out individual is not an adult quite yet. Is that the mantle we are looking at? https://www.inaturalist.org/observations/85617028

Publicado por chaffeemonell hace 3 meses (Marca)

Yes, that one is not adult. I would not call the lip flared out at all. if you look next to the spire, you can see the edge of the lip follows the same line as the previous part of the shell.

Publicado por susanhewitt hace 3 meses (Marca)

Try always to feel the edge of the lip while you are still in the field. Or look for a snail with a lip that is unmistakably turned-out. Sometimes it is worth looking for a dead adult shell on the ground. These snails do live in colonies, so where there is one, there are others.

Publicado por susanhewitt hace 3 meses (Marca)

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