Question about red claw crabs

[Naent]

I keep three red claw crabs in a 100 litre tank, and my question is if it's normal that they are very shy and run and hide whenever I get close to the tank?

This what the tank looks like: 34106
(I have some plants on the other side of the tank)

At least, they've never escaped...

[Aeonflame]

Crabs are naturally timid since they are a main food source for many predators. Given time and enough hiding spaces to feel secure they may grow used to your presence.