Worms are instinctive creatures, and they don't lose that instinct once they are in a worm farm.
In nature, their instinct helps them survive, but in a worm farm, that same instinct can get them into a lot of trouble!
Why worms head down into the drip tray:
Worms aren't particularly good swimmers with their lack of limbs and life jackets. When they get down into the drip tray it can spell disaster.
It is best to leave the tap open so that the underground lake is more of a puddle, giving your worms the best chance of survival.
In summer you may even need to do rescue missions to get the worms out of the drip tray and back up into the farm. In particularly hot weather, freeze some of your food scraps before putting them in the worm farm. The worms will then move towards or away from the frozen scraps to regulate their temperature.