Worms are often regarded as a gardener's friend, as they break up and aerate the soil. However, there are different kinds of worms. The earthworm that you might see wriggling when you dig up a clod of earth is very different from the worms that you find in compost or manure heaps. There are a few kinds of these worms, but very common are brandlings. These are notable by the fact that you can see delicate stripes on them, as you can see in the picture above. They are biologically adapted to the warmth of manure/compost heaps and cannot live in the cooler soil, so when you see a TV gardening presenter casually chucking a worm from his/her compost heap onto the garden, he is doing it no favours.
Compost worms can be found in any compost bin or heap, but there are specific worm composters available that can be ourchased. The simplest can be a bin with holes drilled for the worm liquid, but there are more complicated ones.
The advantage of a worm composter is that it is enclosed to stop the worms escaping, and therefore it can be used to digest cooked food [not meat.] which in an open compost heap would attract rats. Worm compost is very rich and benefits the garden enormously. So the gardener would be advised to have a worm composter. But it is so rich that it is applied sparingly rather than in great piles.
The basic design of all worm composters is to have a space at the bottom for the liquid that the worms excrete to be collected. This is drained away by means of a tap. It smells vile, but it is incredibly rich. You mix it in water at about ten to one or less and spread it around the allotment/garden. Spread it widely.
All worm composters have an area just above the liquid reservoir that contains inert substances for the worms to be safe in. You can use shredded paper, dried leaves or straw. Worms detest acidity and so do not use peat or anything that is acidic.
Start adding food in small quantities just above the safe area. Sometimes mix a little lime in to make the material sweet, as this counters acidity in the food. When the bin is full to the top, you will find the worms in the top section, extract them to another bin set up in the same way as the first one then begin the process again. Spread the worm compost onto your garden. Remember that as it is so rich you cannot simply fill a pot with it and use it instead of soil. It is a soil. Some gardeners collect the worm eggs for reuse, but they are small and hard to find.
A worm composter is a valuable addition to any allotment or garden. They are commercially available, but it is possible to make one.