Two Dead Emerald Crabs in Two Days...

[Eb0la11]

So yesterday I wake up and find one emerald crab on his back dead at the bottom of my tank. I take him out and wonder what could have caused this.

Then today, same thing with my 2nd emerald crab. Both have been in the tank for probably 3 weeks doing ok until now.

I have heard clicking sounds in the tank... Do you guys think theres very little doubt a mantis did this? Both crab's show almost no signs of being attacked. They look in tact. I dont think this is their molt either as its not a thin empty shell, its the whole crab...

What do you guys think I should do? I have about 15 rocks in my tank. I think I could narrow down the mantis' home to maybe 4-5 of them though if that is indeed what I have.