(To paraphrase UB40 ...)
Some months ago I was working on the plot when I heard a rustling coming from the compost heap. I am not one of those people who jumps on a chair at the merest hint of a mouse, but my skin crawled at the sight of a rat crawling through my kitchen and garden waste.
I left the rat to it, hoping that it would fall prey to the regular baiting programme in place on my allotment site to deal with the pest problem. But this week I was reminded of the issue of rats on compost heaps, and allotments in general: there was a reader's question about it in one of the gardening magazines I read, which annoyingly I now can't track down and I caught a programme on Radio 4 dedicated to the issue of Britain's growing rat problem. Then on visiting the plot today I noticed a sign warning allotmenteers to look out for (and alert the correct authorities to) any dead rats after the latest lot of bait was laid.
I am sure there are no rats in my compost heap at the moment - it's pretty sponge-like given the recent rain. I did fall prey to a mouse infestation in the past when I had a Dalek-type plastic compost bin in my garden. I'd failed to mix the browns and the greens properly*, and a mouse had made itself very comfortable in a big lump of shredded paper, until I scared the life out of myself - and it, probably - by lifting the lid to take out some compost. A good mix with a fork put paid to the mouse's papery pied-a-terre and it must have found digs elsewhere as it didn't return.
I think it bears repeating that, as it explains in this Garden Organic factsheet on composting, rats or indeed mice nesting in your heap is a sign that it's too dry. But presuming they're already there, should you worry? In answer to the first point, you should worry a bit - they're a danger to human health and their gnawing can do a lot of damage. But (yes, there's always a but) as this information sheet from the composting group York Rotters points out, it's not the end of the world to have a rat in your heap, provided you wear gloves while handling composting material, turning the heap and so on.
But, presuming you've decided the rats have to go, if only to avoid the prospect of a furry surprise one day when you give the heap a stir, what can you do to evict the little blighters? The sage advice offered by Garden Organic is to "add water until it has the consistency of a wrung-out sponge". The aforementioned magazine suggested weighting down the heap with bricks to ensure no spaces were left for rodents to inhabit. I remember a work colleague of mine saying he'd constructed a completely rat-proof composter but I never got the full details from him: but the York Rotters do have some practical tips and also suggest various commercially available ratproof bins.
*(You can read an extract of my book on the subject of composting here.)