Question on size prey

[Death Shrimp99]

Yesterday i fed my Odontodactylus scyllarus witch is about 5 inches a crab that was about 4 inches(the shell from side to side) and it took my mantis about a half hour to kill it. It seemed to be afraid of it by hideing. And it lives in an eclipse 6 gallon with a rock in the middle of the tank after a while the crab tried to bury itsself bit later the mantis killed it. The crab clearly did not pose a big threat to the mantis's life. Why was my mantis so afraid, i heard mantis shrimp can kill things even bigger than them why is mine weak? i feed it live food at least twice a week in addition to frozen squid and shrimp. What would most mantis the size of mine do?

 

[Balor]

i dont have a mantis, or have i ever had one but taking my experience from most predators, he's been spoiled with smaller prey on a regular basis, he didn't want to potentionly hurt himself with a huge prey item like this.....this is all just a hypthosis