yes, I have an indoor >0.5 kg worm population in a normal environment (soil + food + leaves and branches on top). I think those should be happy, let´s see what happens to the wood explorers! :)

I know that worms can chew the cellulose of the wood chips.

No, they cannot since they have no teeth. It is a good thing that you are doing this as an experiment and I am curious on the outcome based on what I have read in the past. I will share it with you not as a critic but as something to be cautious about. I have read that one has to be cautious about adding wood chips or saw dust to a worm bin for heating up. It happened when a vermicomposter in another worm forum used saw dust pellets to soak up leachate and added it (handful by handful over time) to the worm bin and that caused the bin to overheat. IMHO, it is possible that the MO in the saw dust accellerated the heating up.

In time you will get mites and other critters in the bin and they will help break down saw dust. And eventually, mixed with wormcastings it will become "soil".

I believe the bacteria that break down wood require a lot of nitrogen to do the work so I'm thinking that nitrogen will have to come from any green food sources you add which also must be broken down by bacteria and other bio-critters first... my guess then is it will take a longer time for the bin to begin to cycle and eventually finally achieve a natural balance.

sawdust is good for thermophilic composting.....vermicomposting if its aged for a few years outside exposed to elements. Otherwise its too tough.

If you can collect some isopods (sometimes called pillbugs, sow bugs, roly-polys, or many other regional nicknames), and add them to the bin, it might help to accelerate things. Isopods seem to enjoy high-cellulose living conditions like woody material, and their gnawing can help to shred that sawdust down to make it easier for microbes and worms to process.

@ 11otis :

I know its a very late post but if you see this, will you elaborate on this "MO" of wood sawdust that you refer to in your post? That is a reference i am not familiar with. What is M O short hand for?

-that being said, i have not personally come across any situations where woody materials produced (their own) heat.

ryan, I think the "MO" that 11otis is referring to is Micro-Organisms. Somebody please correct me if I'm wrong on that.

Re the sawdust.......I agree with those above who say worms cannot "chew" sawdust and that you can get heating if you add your N-rich food scraps to the sawdust. This past fall I came across a recently dumped pile of fresh wood chips, probably from a tree trimming outfit. Because the chips were from living trees and were moist enough, the pile had already become quite hot about 6" under the surface. And that was with no addition of any obvious sources of high N material. I guess the green chips had enough N of their own to start the pile heating up.

I have used aspen shavings (under landscape cloth) to hold any excess moisture in my worm bins but not as the actual bedding. I thought it might also soak up any nutrients from the leachate and could be added to the garden or compost pile when I harvest the castings.

Let us know how your experiment turns out.

Harry

Just a smattering of excerpts taken at random from websites (I just did a Google of sawdust composting)...

"Sawdust acts as a ‘brown’ compost material, similar to dry leaves.
Sawdust does a great job of adding carbon to your compost. To have an
ideal compost you’ll want a fairly even ratio of brown and green
materials, or carbon rich and nitrogen rich materials." http://compostbin.org/composting-sawdust/

"If fresh sawdust is put onto the compost heap or directly onto the soil,
it leaches nitrogen from the soil and the plants. Sawdust is very high
in carbon and the bacteria which digest it require nitrogen to do so.
If sawdust is added to the compost heap, extra nitrogen must also be
added" http://www.gardenandflowers.com/about_6618376_sawdust-composting.html

"When composting sawdust, you will want to treat the sawdust just as you would dry leaves, meaning that you will want to add it in an approximately 4:1 ratio of brown to green materials." http://www.gardeningknowhow.com/composting/ingredients/using-sawdust-in-your-compost-pile.htm

"When it comes to sawdust in a compost heap, a little goes a long way.
According to the University of Illinois Cooperative Extension, sawdust
provides needed carbon in your compost heap, but its small particle size
can negatively affect compost aeration. Add too much sawdust, and
you'll quickly find yourself the proud owner of a compost heap that
won't decompose. The oxygen-loving bacteria responsible for most of the
decomposition in your compost heap cease microbial activity in the
absence of oxygen. Avoid this problem by making sure you add plenty of
other carbon-based organic waste to offset the density of the sawdust in
your heap." http://www.gardenguides.com/109560-compost-sawdust.html

Keep in mind the links provided above are referring to a "compost" pile as opposed to a "worm bin", tho I am sure the same interaction with greens will apply.

Yes, thus explains the 4:1 carbon/nitrogen ratio in the third quote... whereas I think 30:1 is more conducive to worm bin safety (at least from all the Internet reading I've done). The lower the ratio the hotter the compost pile provided enough mass is attained. The more curious statement is the last quote about pure sawdust lacking in oxygen.... that's something one wouldn't necessarily think of but I've seen piles of wet sawdust and must concede that it doesn't appear much oxygen would likely penetrate it so I can see where it would be a real concern in the bin being as how the worms depend upon aerobic bacteria for "pre-digestion".

Short version: I’m fairly sure that using sawdust will be fine, but I’d hesitate to use in complete replacement of all other beddings, or bit by bit at first. The issue mentioned above - of it getting too compacted and not enough oxygen - would be the main issue, and having ‘structure’ to the bin to keep it loose would be good, so keep adding shredded cardboard, for example. Also, add the sawdust bit by bit at the top so that there is oxygen and it will get incorporated over time - maybe a layer of an inch or two at the top. This would also let the necessary microorganisms - which are different than for cellulose - to reproduce and catch up. Alternatively, take some material from the worm bin and mix it with sawdust separately and let it sit for a while. At any rate, since it’s an experiment, don’t overdo it at first and see how it works.

TL;DR version:

There are two issues with sawdust. First, that it can compact quite a lot, blocking oxygen necessary for the sawdust to decompose; this is easy to deal with by not overdoing it and adding bulkier stuff like cardboard, or as I suggested above, adding it in layers on top. Second, the dominant material in compost is lignin (the hard stuff in wood), not cellulose (the pulpy structural part in many plants), and there are a lot fewer organisms that can consume lignin. Many of those are fungi. Also lignin takes longer to break down.

Now, this isn’t (IMO) an issue because worms have all sorts of organisms they carry around to help decompose stuff, including some fungi which will also be in the bin.

The comments about sawdust and wood chips in soil ‘tieing up’ nitrogen aren’t (IMO) relevant to a worm bin; it’s an issue in soil because the nitrogen isn’t available to other plants to draw up in their roots. But in a bin, it just means that the organisms are eating the lignin and the worms will eat those organisms eventually (in one form or another, i.e. maybe after they die or are eaten by other organisms). If there are other kitchen scraps in the bin, the worms will have enough to eat.

Personally I think it’s not important whether the worms ‘eat’ (digest) or ingest (pass the sawdust through their bodies) or don’t at all. In each case, the sawdust and lignin is being exposed to the organisms that eventually consume the components of the sawdust - and the worms eat along the way too.

Because the organisms that consume lignin are a bit specific and slower-acting, they will probably need more time to reproduce and be large enough in number to eat the sawdust in quantity - will also depend how ‘green’ (fresh) the sawdust is. Worms probably won’t be able to subsist on sawdust-bedding alone as well as they seem to be able to with cardboard and paper - cellulose is easier to break down.

Finally, it’s quite likely that the sawdust/lignin won’t be consumed as completely as, say, cardboard. That’s okay, partially-consumed lignin is a normal component of many types of soil and humus in particular, it’s the (mostly) stable - stable in the sense of no longer decomposing actively - lignin and other stuff. It may have a slightly different consistency than regular vermicompost, but nothing critical.

I’ve put plenty of sawdust in compost piles, it eventually turns brownish-red and has a rich earthy smell. I’ve only used a bit from time to time in worm bins, though.

At any rate, experiment and let us know how it works out.