Woodlice

[Wong]

How do you get rid of woodlice that have made their home under the floorboards beneath the bath? Does this mean there is damp there or do they like any environment? 

[gen2]

Yes this probably means there is damp there.  Woodlice (slaters) dry out fairly readily and therefore need a moist environment.
This could be the best scenario. This is where the woodlice are feasting elsewhere and just dossing down in a damp corner.
The worse situation is that you actually have rotting timbers beneath your bath.  Woodlice gain most of their nutrition from the fungi (moulds) that break down woody tissue, so the timbers under your bath may not only be moist, but actually rotting.
As to getting rid of them, you have to find the source of moisture and repair it.  Problem solved.

[Wong]

Thanks very much gen2.