Why are worms all congregating in the lid of my compost bin?

I don't know about you but I often get asked this one.

You know the scenario you go down to the garden to add your latest batch of tea bags and vegetable peelings into your bin.  You take the lid off and dozens of worms are all huddling into the lid almost as though they are trying to get out... I've asked all manner of horticultural experts and ecologists this one and nobody seems to have the answer.



I have heard that sometimes compost worms migrate, and that they do this in a herd like this, so maybe yours are trying this and then just getting stuck when they encounter the lid???

The most logical explanation I can offer is that the worms are likely to be finding the conditions in the compost unpleasant for them and are trying to get away from it.  Now worms are sensitive little creatures, bless them, so they could be unsettled by a number of factors such as pH, oxygen concentration, temperature or moisture content. 

So....it could be an indication perhaps that your compost is perhaps also too wet.  The worms won't be able to breath is the waste is too waterlogged so they will be going to the top for a breather.  We tend to put in loads of fruit and vegetable matter which has alot of moisture content, so this doesn't help.  So you could try putting some dry material in, such as newspaper, this will dry it out a bit.

It could be that your worms are unsettled by the pH.  In terms of pH, although composting tends to produce a relatively neutral (ph7) compost, in the early hot stages of composting there is likely to be a slight increase in acidity due to the presence of natural humic acids.  The other thing is of course if you are adding in alot of fruit peelings especially citrus fruits you will be decreasing the pH this way.  So perhaps avoid adding lemon and orange peel in such amounts or alternatively try adding a bit of lime to neutralise it. 

My other theory is that the council of worms may have planned a "great escape" and that they are waiting until you lift the lid then making a bid forf freedom over the top!


Anyhow I wouldnt worry about it too much, worms are mobile so if they dont like something they can get away from it and ultimately they have access to the ground so they could get out of the compost by tunneling down if they really weren't happy.