Re: empty shells are they empty dinner plates or just vacant

Well I'm no snail expert but, thanks to your question, I have had make a 
quick step toward being one.

For your information, there is an extensive range of information the 
numerous varieties of Mollusca Gastropoda Pulmonata (or freshwater 
snails).

If you're really keen check out the links on  http://
www.fw.umn.edu/Personnel/staff/Hove/Mussel.web.sites
Most are university links here so the information can be trusted.

The site that most helped me in my rushed research for you was The trail 
of the snail which is at http://members.t
ripod.com/arnobrosi/aquasnail.html

However, if you just want an answer to the questions you asked then...

In short, yes you are finding the reminants of a meal.  Snails are 
connected to their shells by a muscle on their body, the same connection 
that allows them to quickly retract into hiding.  Unlike hermit crabs, 
who outgrow their shell and move into another, the snail doesn't willingly 
leave its protection.

Snails are the minature cows of your lake, spending their time grazing on 
algae and plants.  Being slow and with minimal defenses they have an 
extensive list of predators from parasites to fish, from other molluscs 
to water birds.  Not all of which would leave the sign that the snail was 
pulled out of its shell.

Other than the protection of their shell their other defenses relate to 
hiding away where they can't be found and/or feeding when their predators 
are not.  The fact that you hardly ever find one living is testimony to 
the fact that they do this quite effectevely.

If you are trying to find some living ones I suggest you check out a 
handbook on doing so.  Provided by Freshwater Mollusk Conservation 
Society Committee on the Status & Distribution of Gastropods, this link 
would be very helpful to you.  It will also help you identify ones you do 
find (shell or whole). http://www.cofc.edu/%
7Edillonr/Dillon_FW_Gast_Chptr.pdf

Please remember that you cannot take animal or plant matter from some areas 
including national parks etc.  In fact I suggest you don't take anything 
from anywhere.  After all what you take may deprive something from a meal 
or a home.  Even empty and deteriorating shells return nutrients back to 
the lake.  Also note that some cone animals are extremely poisonous in 
some parts of the world (eg. where I'm from - Australia).

All the best.

Peter