Apparently the creature sleeps by daytime.
3 seconds sound clip from the Attack of the Crab Monsters (1957) movie soundboard.
You can hear this line at 00:45:49.046 in the DVD version of the movie.
Quote context
[...]
- That proves that the crab is negatively charged.
- Yes. Then, Hank, you must create a trap of positive energy.
- Well, sure it does, doctor. Easier to build than a model airplane.
- That's fine, Karl, but how do we get the crab to step into it?
- Apparently the creature sleeps by daytime.
- We must take the arc and place it in one of the well-traveled cave routes.
- He has eight legs with which to step on the plate. I am sure he will manage.
- He is using the dynamite. We must hurry.
[...]