Many people are curious about using Red Composting worms in their outdoor composting bins. There are a few things to keep in mind if you decide to do this. Red Wigglers or Eisenia foetida are not indigenous to Northern climates, they are more tropical in nature and will die if left to freeze over the winter. There is of course nothing stopping you from simply moving some inside in the Fall to over-winter in the basement. They’ll need some maintenance in an indoor bin but most folks find this a good compromise. You can also just buy new worms each spring though we don’t recommend this and over-wintering a bin is really easy. http://www.naturesperfectplantfood.com/2011/11/15/easy-worm-bin-photo-essay/
If you have a large enough compost heap, not bin, you may be able to keep your worms alive in the depths of cold. We’ve been successful in that way over the years in Winnipeg and as you know, have kept our operation South of Stienbach outside the entire time. Those worms thrive because they’re grown in one ton piles of cow manure, which as you can imagine generate quite a bit of heat all on their own.
Another point of interest is the habits of the worms themselves. As “leaf litter” worms Red Wigglers occupy a certain layer of material. Under the “leaf litter” yet above the top soil. Picture a pile of old fallen leaves, when you flip it over you will always find a thin layer of decomposing material; this is the zone. So, if you choose to have worms in your outside bin, you will need to have some form of mulch on top to mimic leaf litter and protect your colony. You will also need to keep an eye on moisture levels, dry worms are dead worms.
The benefits of using worms in your composter are many; you create a superior product in the form of castings when compared to traditional compost and you will speed up the composting process. The worms will live in the top 12 inches or so of the compost so you will need to occasionally mix or turn the material to keep the food supply readily available.