Snail graveyard; possible mantis

[Matt]

I'd like to see the critter in the light so I'd have a better chance of identifying it. I looked over some of the shells again, and none of them are smashed. Something is killing them in that particular area, though, unless there's a huge coincidence that I've just found where snails go to die.

Sadly, though, given that whatever it is has been in the tank since I bought that LR (over a year ago), and this is the first time I've got even a shadowy glimpse of it, I don't like my chances of entertaining friends with the escargot-feeding.

I don't have any hermits, or any other non-hitch-hiking crabs in that tank. I wonder if one of the hitch-hiking crabs (perhaps the big spidery-legged one) could be the murderer? I caught all three crabs right in that area. I blamed the shadowy shrimp-like creature - but might it be an innocent?