Over the past few years that we have been involved with Vermicomposting there is one question that comes up again and again, "I have worms in my backyard, can't I just use them?" The answer is "yes" and "no". "Yes" because the worms that are used primarily for composting may well be found in your yard eating some decaying leaves or other pile of organic matter. However the answer is also "NO" because there is a lot of confusion about worms, this is where being a bit of a science geek comes in handy. The thing that most people think of when you say worms is Night crawlers, that is the large (2 1/2-6 inch) brownish gray to brownish red worms that are found littering parking lots after it rains. Night crawlers belong to the "Earthworm" family or Anecic worms specifically Lumbricus terrestris which prefer to live in vertical burrows that they dig in the dirt, they do not like to have their burrows disturbed since they come out to feed primarily at night (hence the name) and retreat to their dark burrow in the day. Night crawlers eat some decaying organic matter such as rotting leaves and they also process dirt for nutrients, thus their castings (poop) is beneficial to gardens and lawns like most any worms.
This brings us to Red worms aka red wigglers, tiger worms, manure worms to list a few common names, these small (1-2 1/2 inch) worms belong to the Epigeic worm family (Scientifically-Eisenia foetida or Eisenia andrei) which lives in as well as above the top layer of soil, they can commonly be found gorging themselves on well rotted livestock manure or leaf piles, they do not form burrows but rather simply seek out habitable piles of rotting organic matter and eat their way through it then move on. Their name comes from their dark red coloring and the fact that they tend to wiggle or jump when handled. They, like most worms prefer the dark so you rarely see them unless you disturb their garbage pile and since they do not have burrows, they adapt well to captive living. Red worms consume more organic matter than night crawlers (about half their weight in a day) which makes them so great for composting.
So as you can see, not all worms are created equal, both are beneficial to gardens and lawns, both feed on organic matter, and both are slimy but when it comes to getting rid of garbage, red worms are the way to go.