I have a ton of snails, probably over 100 and about 5 crabs. I used to have WAY more crabs, but if I saw a crab chomping at a smail, he got thrown out. Litterly....opened up the door and out he went. I'm down to a few crabs that won't eat my snails. :lol:
Thats the beauty of living in Okinawa. You don't have to call a supplier for more crabs/snails. I figured out once how much it would have cost me to buy the exact (estimated count) CUC that I have...and just estimating, I would have spent around $700 in just snails (from liveaquaria.com)....and I gathered it myself here.... amazing.
But to anwser your question, I have few crabs, and a ton of snails. My snails do a good job at keeping my tank spotless. What crabs I do have, I think enjoy the fact they are the few in the tank and never go hungry...