In message , David
writes
On Sun, 11 Mar 2018 11:23:38 +0000, Ian Jackson wrote:

I have three 'Dalek' compost bins at the end of the garden. They are
standing on the ground, side-by-side, in a row.

They all get fed with the same sort of stuff (kitchen vegetable waste,
dead plants, small garden material etc).

Whenever I go to put something in them, more often than not when I lift
the lid of the middle one there's a mass of worms having what looks like
a serious sex orgy (and there are also quite a lot of them on the
underside of the lid). It is very satisfying to see them all having such
a good time. However, in the other two bins, there are almost never any
worms to be seen.

If I transfer some worms from the middle bin to the other two (usually
by swapping the lids), next time I visit the bins the situation is
exactly as it was before (ie no visible worm activity in the two outer
bins). Despite this, the contents of all three bins seems to be
composting away at about the same rate.

So the question is, "What's going on"?

Have you tried, fort instance, removing the top 10% from the centre and
one outside bin and swapping them over?

That might be more significant than just moving a few worms over.

Yes - I've done that.

This has been going on for years. No matter what I do to populate the
outer bins, within minutes the worms I've transferred disappear - and a
day or two later they appear back in the middle bin (but of course, I
have no idea whether these are the same worms as the ones I evicted!).

However, I'm not too worried. All three bins seem to be composting the
stuff I put in them. However, it's nice to be able to see those who are
doing it. Note that later in the year, loads of woodlice and large slugs
also move in to help the worms. I don't think they are quite as fussy
about which bin they occupy.
--
Ian