Bin does not get enough air. To aerate, add fresh bedding and mix bin contents daily. The food in bin is naturally smelly. For instance, we have found that onions and broccoli do not smell very pleasant when they decompose in the worm bin. Simply remove any food source that smells bad from the bin.
Bin contains non-compostables.
Meat, bones, dairy and oily products should not be fed to the worms because these items become rancid when decomposing. Bin is too wet and worms are drowning. Bin is too dry and worms dry out. Bin does not get enough air and worms suffocate. Worms do not get enough food.