The most likely reasons for the failure of a Wormery are the following:
1) Overfeeding in the early stages
The worms need a little while to settle in and the food waste you add needs to partly (rot) decompose naturally before the worms are able to eat it. The first few weeks are the slowest and you should generally only feed a couple of handfuls a week when you first set it up. Once the worms are established and the food is in the correct state (rotting) for the worms, you can increase the throughput.
2) Conditions get too wet
If the food waste in the Wormery gets very soggy and wet, then this can cause problems for the worms. With the weight of the water in the waste the waste becomes compacted and the air is pushed out of the waste. Worms need air. Signs of this are as follows. You might find they try to get away from the food waste – they will be at the top of the wormery on the sides. You may find the worms have disappeared – they could be in the sump. If this is the case, it is likely the worms have drowned in the liquid in the sump. The sump should be drained regularly, please note most fruit and vegetable waste is 85% water.
It is an easy problem to solve, however. If the waste is looking wet (soggy), if you took a handful and squeezed it hard, if water runs out between your fingers it is too wet (damp/moist is good!) then simply shred up cardboard egg cartons (are preferable) or newspaper and mix this thoroughly into the Wormery right down to the base plate or bottom of the tray. This will soak up the excess moisture, help aerate the compost, and return the Wormery to the normal operation.
3) Conditions get too acidic
This can be a problem if you add a large amount of acidic food waste such as citrus peel and / or conditions get waterlogged. Pot worms (enchytraeids) are tiny thread like worms that resemble a piece of white sewing thread a few millimetres long. They occur quite naturally and are harmless – in fact they do the same job as the Tiger worms. However, they thrive at a lower, more acidic pH than is ideal for the tiger worms. The proliferation of these pot worms is a sign of acidity – so if this occurs add a handful of the lime mix and combine it with the points above when the waste gets too wet.