15 October 2006

It's a snail eat snail shell world

After almost a year-long break, I resumed my survey of the land snails of Belt Woods, possibly the only tract of old growth forest left in eastern Maryland. (Previous posts on Belt woods are here and here.) The trees in an approximately 45-acre section of Belt Woods are believed to have never been cut. Yesterday, I spent about 3 hours there looking for snails.

Snail shells and the egg shells of most snail species are made out of calcium carbonate. That means that snails need calcium in their diet. In forests of eastern U.S. where there are no limestone or marble rocks and the soil is low in calcium, the snails get some, if not most, of their calcium by eating other snails' shells.

One common species that I have frequently found in the process of eating empty snail shells is Ventridens ligera. I encountered 2 such individuals yesterday. On both occasions, the snails were in damp, loose soil under pieces of wood or tree bark. The first V. ligera (picture below) had consumed most of the body whorl of the partially empty shell of another V. ligera. The red arrows point at the remaining jagged edges of the body whorl.

Vligera3

In the second picture you can see what is left of the shell of another V. ligera covering the aperture of a live V. ligera. The snail was apparently eating the shell from the inside.

Vligera4

As far as I know, V. ligera is not carnivorous. So they wouldn't normally attack other snails, including conspecifics; they probably eat only empty shells or the shells of dead snails.

These observations have 2 implications:

1. Consumption by snails is one of the significant factors that determine the life span of empty shells in areas otherwise low in calcium.

2. Missing sections of snail shells may not necessarily have been the result of a predatory attack, but may instead have resulted from post-mortem consumption by other snails.

11 comments:

Snail said...

Now that is interesting. I knew snails were supposed to recycle calcium from other shells but I'd never seen them do it.

Do you have any plans to document the pattern of damage? It'd make an interesting study.

AYDIN ÖRSTAN said...

Yes, I have a bunch of shells with an identical wear pattern, but haven't gotten around to doing a definite experiment to show that snails were the responsible agents for the damage.

s g said...

My son and I have been enjoying snails for some time now.

The snails in our tank will occasionally prefer an empty snail shell to their cuttlefish bone.

We see many baby snails hitching rides on adults... do you think they may be getting calcium from the adult's shell? Perhaps because of their size, the baby does not leave any noticeable damage?

AYDIN ÖRSTAN said...

Yes, the baby snails may be scraping off calcium from adults' shells. You would need a microscope to see if they leave any traces on the shell surface.

Janice said...

Hi, I've been searching the internet, and this post is the closest thing to answer I can find for this question I have.

I have two snails in my aquarium. One is a pest type of snail that survived from an earlier infestation and has grown to be larger than I have ever seen snails of that type, almost two centimeters tall. The second is one I purchased from a pet store that they called a mystery snail; it is closer to three inches in diameter. They two seemed relatively peaceful toward each other until one day I found the larger snail on top of the smaller. The large snail appeared to be killing the small, but a while later I noticed the small snail cruising around again.

Today I witnessed the encounter from the beginning. The two were both on the wall of the aquarium when the large snail "climbed" on top of the small snail. It then proceeded to grasp the small snail with his whole body, while shoving against the wall with his shell, as if to remove the small snail from the side of the aquarium.

When this didn't work, the larger snail approached the small one's mouth region (I apologize for lack of scientific terms) and sucked the air out of the smaller snail, causing him to release his hold on the wall and sink to the bottom of the aquarium.

The large snail then began sucking away at the small one's face region, and eventually the whole face of the large one was inside the opening of the smaller one. It looked like he was attempting to eat his neighbor.

As I continue to watch, it seems like the small snail is still alive, but I can't think of any explanation for this behavior. Do you have any ideas?

P.S. Do you ever study aquatic snails? Most days I think they are more interesting than my fish.

AYDIN ÖRSTAN said...

Janice: If both snails are of the same species, they may be mating.

Can you take pictures next time you find them on top of each other & send me the pictures?

I don't think there are any carnivorous aquatic snails, although I may be wrong.

Janice said...

They definitely are not the same species.
Unfortunately I do not have a camera. I tried taking a photo with my camera phone, but it didn't work out.
I really don't think the bigger one was eating the other one, but it was really strange all the same.

Anonymous said...

okay i had two snails in a tank. one big one small.they were the same spices and the only animals in the tank.when i left this moring they were both there but when i came home only the larger one was there. the lid was on i cheeked everywhere including the filter there was nothing left... could my large snail have killed my small snail or my small snail died and my large snail eaten it?

AYDIN ÖRSTAN said...

I would search again. The small snail could be hidden somewhere.

Carey said...

I had two snails in a tank together but I had to separate them. I think the larger snail has eaten a hole in the smaller snail's shell. I found the larger one on top of the smaller one and when I pulled him off there was a hole in his shell where there wasn't one before.

Anonymous said...

I accidentally stepped on a snail and it appeared that several of its mates came to mourn its death. They were also climbing on it and possibly eating its fluids. What may be happening here, felt very guilty!