Signs of excess moisture
Constant condensation, saturated substrate, standing water, recurring mould and a terrestrial repeatedly avoiding the ground can all suggest the enclosure is too wet. One behaviour on its own is not proof, but the pattern matters.
Why it happens
Over-misting, poor ventilation and large volumes of water added to the whole substrate are common causes. Small enclosures can stay wet far longer than expected because there is little air movement.
Do not panic-dry
Do not suddenly move a settled spider into bone-dry substrate unless there is a genuine emergency. Increase ventilation where safe, stop adding unnecessary water and allow the enclosure to move back toward a useful gradient.
Species context
A moisture-dependent Asian fossorial and an arid-adapted New World terrestrial should not look the same. Judge wetness against the species' normal ecology and life stage.
Slings
Tiny slings can need dependable moisture but are also vulnerable to stale, waterlogged conditions. Use small controlled amounts of water and good ventilation rather than soaking the cup.
When to rehouse
Rehousing is justified if there is flooding, foul substrate, dangerous mould growth or a design that cannot dry safely. If the problem is minor, fixing the watering routine is less disruptive than a complete teardown.