The Casing Starter from Mushbox.com is one of the key ingredients to the success of the Mushbox Casing Kit and probably any casing kit that uses soil or dung as a substrate. Basically its microscopic biological warfare, you could even consider it nano-mycology! The mixture inside the casing starter contains a sample of soil combined with an elite type of Nematode. A Nematode is a microscopic worm that has only 1 purpose, to feed on fly larva, and fly larva are everywhere, especially in your casing soil.