Insects on compost heaps

by Richard Jones

My two compost bins are being very productive. As well as yielding their first crop of usable compost... they are also home to a heaving mass of wildlife.

My two compost bins are being very productive. As well as yielding their first crop of usable compost, now spread over back and front gardens to great effect, they are also home to a heaving mass of wildlife. Every time I open the lids a great cloud of flies emerges.

Fruit flies (at least two Drosophila species) feature strongly, which is no surprise given the amount of apple cores, banana skins, melon shells and potato peelings we chuck in each week. Although the adult flies are only 2.5mm long, they are so numerous in there that their maggots can work through several bucketloads of kitchen waste each week.

These are sometimes joined by the smaller, but more delicately fluffy 'moth flies'. I haven't tried to identify these little creatures, even though (believe it or not) I do have a monograph on them. They breed in various types of decaying organic matter and are apparently common around sewage works. I've found several different types over the years: a fuzzy golden one in a treacherously boggy wood in West Sussex; a black one in the New Forest; a grey one breeding in the overflow of the rather unsavoury bathroom basin in a student flat when I lived in Brighton; and these almost pure white ones in my current garden. They look very good against the blue of the wooden compost bins. Yes blue. They match the shed and aren't really that bright - they've weathered to a dark rustic tone.

And feeding on the fly maggots is a whole series of other insects. There's a veritable ecosystem in there. Several species of rove beetle regularly turn tail and disappear into the morass when I lift off the lids. Last week I found a shiny black domed beetle about the size and shape of a kidney bean - Hister merdarius. It's very scarce, so has no common name and being shiny, black and domed is about as easy to photograph as a black hole. Sorry there's no picture of it here.

In our previous house, over in Nunhead, I regularly used to find a small but stout grey-brown chafer-like beetle sitting on the window sills or outside the back door. Trox scaber had been attracted to the lighted windows as it flew past. It was an unusual thing to find in the garden since it is a well known denizen of owl nests in hollow trees. Here it feeds on the leftovers of the owl kills and the undigested bits in regurgitated pellets. No owl nests where we lived and my supposition was always that it was breeding in local compost bins into which residents had been tipping, contrary to the usual advice, bones and meat products.

We're pretty gung-ho with our composting habits, but I draw the line at bones. Much else goes in though and the consistency of the resulting compost gives a clue to one food item we may be need to rethink. My first foray into the bottom of the mouldering earth produced a fine harvest of rich dark soil ... full of egg shells. Oh well. They soon get broken into pieces as we mulch them in; they'll help improve the drainage.

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Gardeners' World Web User 29/05/2008 at 06:07

The two giant compost bins in our garden (thanks, Stroud Council!) doing fine. But imagine the surprise last summer when I discovered at least three grass snakes in there. This spring, whilst taking the bin apart, I found what I had hoped to find: remnants of egg casings from the snakes. In a recent programme on the Baltic states it was mentioned that these snakes were venerated and worshiped there. I feel privileged.

Gardeners' World Web User 29/05/2008 at 09:33

It is amusing to see adverts and articles extolling the benefits of compost making, and illustrating the animals which are found in compost bins - but omitting any mention of insects, these seem to be the most prominent life associated with our compost heaps. I suppose insects are not normally a polite subject? When does it seem sensible to stop adding to a compost heap and start another? Clearly a heap which appears full can be a foot lower in a few days, like a magic porridge pot in reverse, in fact.

Gardeners' World Web User 29/05/2008 at 12:24

Hi. I have just read all about Insects on a compost heap, and I would like to add that for the last 3/4 years my compost has been infested with wood lice, and I mean infested!Thousands of them. I have moved the compost site 4 times and still the blighters multiply. Can I use this compost? I'm worried the wood lice will eat my plants. Would this be the case? I would point out that we have several very large fir and silver birch trees in the garden. Regarda Angela Alden

Gardeners' World Web User 29/05/2008 at 16:31

Just got another compost bin today given to us by a friend our first one has some lovely usable compost in it at the moment which we've been using to grow potatoes in. We didn't want to add anything else to it so the weekend grass clippings can start off the new one. We're going to compost cardboard in this one as well. We have noticed the wildlife in the first one and along with frequent turning the stuffs composted in no time at all.We also added the odd bucket of pond water with algae and duck weed in it, keeping it moist certainly helps.

Gardeners' World Web User 29/05/2008 at 19:39

Don't worry about the egg shells, they will help keep the slugs at bay!

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