Biodiversity in a kitchen waste recycling bin

Today's Guardian Country Diary is all about the contents of our garden kitchen waste compost bins.

We have been recycling all of the vegetable waste from the kitchen, together with garden weeds and fallen leaves, for about 30 years now, using three black compost bins. During that time we must have produced tons of compost that has all been dug back into the garden, which is now a very fertile plot.

These are some of the organisms that do all the recycling work.

The first organisms to colonise the vegetable peelings and fruit skins are fungi. I suspect that this might be a Penicillium mould, which often grows on the skins of rotting citrus fruits.

This is the rather lovely pin mould, Mucor mucedo, with glassy hyphae and sporangia that look like beads of polished jet.

This, I suspect, is Botrytis, a common coloniser of dead vegetable matter.

Currently there are thousands of these tiny moth-flies (also known as drain-flies or owl-midges) in one of the bins.

They breed in vast numbers during the early stages of composting, when the bins are less than half full....

.... and provide a food source for some of the predators that live in the bins, like this small spider that has an egg cocoon under the bin lid.

The bins are home to a lot of slugs, that consume decaying plant material and are useful all the time they stick to this diet, though in spring they become a nuisance if they consume seedlings in the garden. 

To minimise that risk I raise plants in posts until they are large enough to show some degree of slug resistance when I plant them out in the garden.

A black snake millipedes, that feeds on the decaying plant material and probably on some of the fungi too.

As the composting proceeds and the bin contents become drier the numbers of these minute springtails increase. When you lift the lids they pole-vault into the air, using the special structure called a furcula under their tail end.

And finally ...... the most important recyclers of all, brandling worms Eisenia fetida. When composting is at its peak there are hundreds of these in each bin. 

Much of the compost that ends up in the garden has probably passed through the digestive system of one of these worms.

Getting a grip..

We've got three black compost bins in the garden that recycle most of the garden waste and all of the plant-based leftovers from the kitchen, so they provide a constant source of compost for the soil. The animals in the bins that do much of the recycling work are these brandling worms Eisenia foetida, aka tiger worms, aka European nightcrawlers.

A curious feature of these worms, apart from their rather attractive tiger stripes, is that they often climb the sides of the compost bins and can easily scale vertical surfaces, often attaching themselves to the inside of the bin lids. 

If you take a look at the next picture you can see how they climb .........

Each segment of an oligochaete worm like this bears stiff, retractable bristles called chaetae, which are the little white projections that you can see in the picture above. The moisture on the worm's body makes it naturally slightly sticky, but it's these bristles that grip surfaces as it alternately extends and contracts its body as it moves forward. 

In the picture above the worm is contracting the longitudinal muscles in the front part of its body so that it shortens and becomes fatter, dragging forward the segments behind whose chaetae have temporarily retracted. 

Next the chaetae on the forward segments will retract as their circular muscles squeeze them and make them longer and thinner, stretching forward, while the bristles in the segments behind will extend their chaetae to provide grip.

If you place one of these worms (or a common earthworm) on a sheet of paper and listen carefully you can hear the scratching of the chaetae on the paper as the worm wriggles.