Good question from Judith:
Could you elaborate on the “blue worms” – you say they are good composters, but seen as pests. Why would we not want them? Do they take over? What is the down side of them in the bins?
Blue Worms (Perionyx sp.) grow quickly, produce lots of offspring, and consume lots of waste materials when conditions are favorable for them. This is what makes them a great composting species. BUT in these situations (when conditions are favorable) they can also basically take over systems where other worms, such as Red Worms or European Nightcrawlers, are present. SO, you may see the numbers of these other worms gradually decrease over time.
In cases (usually in warmer regions) where worm farmers are trying to grow pure cultures of Reds or Euros, it can (understandably) be frustrating when Blues infiltrate and become established. This is why many people refer to them as “pests”.
Temperature is probably the main factor of importance. Temps between 70 and 86 (~ 21 C and 30 C) tend to be very favorable for Blues, and it’s when a system is in this temperature range for extended periods that the Blues tend to dominate.
On the flip-side, these worms also tend to be pretty cold-intolerant. Down below 70 F (~ 21 C) or so, they can really slow down and become far less effective for vermicomposting – and they’ll usually start to die once temps drop down below 50 F (10 C). This can be frustrating for those living in cooler regions (vermicomposting outdoors), since it can become necessary to replace your worms periodically.
Red Worms and European Nightcrawlers remain effective at lower temps (than Blues), and will basically only die if they freeze solid.
Blue Worms can also be somewhat temperamental – prone to roaming – even outside of the system – without much warning (whereas Red Worms and Euros tend to be more mellow – although Euros are a fair bit more temperamental than Reds). Various factors, such as a change in weather, excess watering, hunger etc can be responsible for this.
Bottom-line, it all comes down to your overall goals and tolerance. If you are planning to keep your system(s) in a climate-controlled location (with warm temps), and are keen to quickly convert as much waste into castings as you can, Blue Worms are a great choice. And lots of people swear by them (while others swear AT them – haha).
If, on the other hand, you’d prefer a more “mellow” worm and/or your system(s) will experience fluctuations of temperatures (and conditions in general), you are likely better off to go with Reds or Euros.
As far as Blues that hitch a ride in Red Worm or Euro cultures goes – my advice is not to worry about it TOO much. Not every batch of Reds and Euros has Blues, and even when they do, they tend to make up a relatively small proportion of the total population.
(Except in the case of suppliers that sell 100% Blue Worm cultures as “Reds” and “Euros”…grrr!)
Whatever your final conclusions about all this end up being, I highly recommend learning how to properly identify the common composting worm species (the Red Worm Composting Facebook group is an excellent place to learn more about this and ask for help with worm IDs).
Hope this helps!