Worms gain their nutrition from the microbes in the soil. They cruise around taking in soil and digesting the bugs in that soil. A good analogy would be to consider a worm is to the soil what a whale is to the sea – where the whale consumes microscopic plankton, the worm consumes microscopic soil bacteria, fungi etc.

Why do we count worms?

The reason we count worms is that they are easy to find because of their size and they give an indication of how active the soil microbial population is. Put simply, the better the microbial population, the more worms you will have because the soil microbes represent a source of food. The fact that the worm eats the microbes in the soil may be seen as a negative as we need those bugs to maintain balanced nutrient and mineral levels in the soil however this isn’t exactly the case.

While worms do digest some of the bugs they take in, they don’t get them all. Plus the bugs that survive the digestive action of the worm spend the time it takes to travel through the worm reproducing. This means that at the end of the journey through the worm, there is actually more microbes in the worm poo (or ‘vermicast’) coming out the back of the worm than there was in the soil at the front of the worm.

What is the ideal number of worms per spadeful?

Most consider the ideal number of worms to be between 30 and 40 per spadeful. To achieve this you need to make sure mineral and nutrient levels in the soil are properly balanced which allows for a healthy population of microbial ogranisms. Of course, the healthier the population of microbial soil organisms, the more available for worms to feed on and the more worms you have.