Frequently I'm asked can I use worms I find to compost? The short answer is "not really".
There are a few thousand species of earthworms, only a handful of which are really good compost worms. All worms can all be lumped into 3 groups that are useful to determine whether they are useful to us for composting.
- Anecic worms - anecic earthworms dig deep vertical burrows that they use over and over. They do not like to have their burrows disturbed and are very slow to reproduce. They eat and breed on the surface but otherwise stay deep under the surface. Their deep vertical burrows provide oxygen to deep roots of plants, allow drainage of water deeper into soil and carry organic matter into the subsoil. These are the most commonly found worms after a heavy rain.
- Endogeic worms - endogeic species dig shallow, horizontal burrows in the top 3 feet (90 cm approximately) of the soil. These are natures rototilliers, moving organic matter into the top root zone of plants. These are still slow to breed but faster than anecic worms. These worms also do not tolerate disturbance well, so aren't suitable for most composting operations.
- Epigeic worms - the epigeic worms are the compost worms. These live above the surface of the soil in rotting organic matter like leaf duff, manure etc. They don't form permanent burrows, as they eat the matter collapses. This makes them more tolerant of being disturbed. Living onnthe surface also makes them easy prey to birds, skunks and other rodents. To overcome this the breed very quickly to replace themselves and ensure survival of the species. Epigeic worms are evolved to eat things that fall on the ground. Things like fruit and vegetable waste is a natural thing for them to feed upon. Because these worms live above the surface it's very rare to find them flooded out after a rain. It's not impossible to find epigeic worms flipping over leaf litter or manure piles but being sure of what you found is tricky. It's better to purchase from someone trusted (not necessarily the one advertising most). This will usually get you started "right" with the best chance of success