“Can worms live on animal manure only, or do they need other supplements?” ~ David Turburville
Worms can indeed be fed only animal manures. These materials are incredibly rich in microorganisms, which worms depend upon for their nutrition. When it comes down to it, animal manures are just about the best materials you can feel your worms!
One of the common names for Eisenia fetida is actually “Manure Worm” – which is very appropriate given its affinity for dung heaps. My first encounter with this species occurred on a horse farm where I was working one summer in my early teens. I dug into an old heap of horse manure out behind the barn (I was collecting some manure for my dad’s garden) and was shocked to see an incredible abundance of fat red wigglers below the surface.
Not all manures are created equal however. While all varieties CAN be used as food for worms, the type of animal and the handling practices involved will dictate how readily the worms will feed on the material. In general, it is the levels of ammonia and inorganic salts in manures that are the most important factors – high levels of either one can be harmful or even fatal, especially if the worms have limited options for escape.
Let’s look at some of the different types of manure in terms of their potential as a vermicomposting substrate.
Cattle Solids – These are materials that have been separated from liquid slurry systems (common in the dairy cattle industry). According to Edwards and Bohlen (1996), these are the ‘easiest’ animal wastes to grow worms in. The fact that they have been flushed with water likely helps to explain why worms will move into these materials more readily than some other manures (salts and urea found in animal urine would be diluted greatly). By the way – regular bedded cattle manure will likely have similar properties to horse manure (discussed next).
Horse Manure – This is also an excellent material for vermicomposting, especially since it is very often mixed with some sort of carbon-rich bedding material (such as straw). Since it is a dry manure (ie not flushed with water), it will likely need to be aged or briefly composted to lower ammonia levels and reduce the chances of further heating in the vermicomposting system.
Pig Solids – Similar to cattle solids, this material has been separated out from a liquid slurry system. This material is thought to be one of the most productive wastes for growing worms, and as shown in various Ohio State University growth studies, potentially results in the highest quality vermicompost as well.
Poultry Wastes – Bird feces in general tends to contain high levels of both ammonia and inorganic salts, thus making less ideal than some other manures. With suffient washing or composting/aging however this material can be used in worm farming systems, and should result in a rich compost.
Rabbit Manure – This material is somewhat similar to bird wastes in that it can contain high levels of salts and ammonia, but with proper handling it can make for an excellent worm food, as many rabbit-breeders-turned-worm-farmers have discovered.
Sheep/Goat/Llama Manure – These too are fairly rich manures, but with some pre-composting or washing these should be well-suited for a worm farming system.
Human/Pet wastes – These materials should be used with caution, and ONLY in systems designed specifically for handling these wastes (ie not the same systems that worms or castings will be harvested from for sale). These will also need to be mixed with ample carbon rich material.