Worming its way into gardeners' affections

ANOTHER LIFE:DARK, DRY AND RICH, crumbly and sweet-smelling: garden compost sometimes earns words more appropriate to Christmas pudding.

I’ve produced much of it, indeed, from well- matured corners of traditional timber-sided compost heaps. But many gardeners this spring are extracting compost from back-door plastic bins offered cheaply by local authorities. What’s dug out through the little hatch at the bottom may seem a lot less appealing: dark, indeed, but soggy as wet peat; fruity, certainly, but with whiffs of farmyard and marsh.

Never mind: it’s all good stuff, like the shovelfuls thudding into my own wheelbarrow. Next time put much more dry stuff at the bottom of the bin, lay newspaper between the kitchen bucketfuls and shake the potato peelings harder. Enough of the tiger worms, I was pleased to see, had survived and even multiplied, the shiny pink tangles tossed back into the bin to go on chewing.

Tiger worms (brandlings, red wrigglers) are Eisenia fetida, a species of earthworm adapted to cope with the heat in fast-fermenting organic material. Sowing one’s vermicompost with the right kind of worm and managing its welfare properly (try ipcc.ie/wormbin.html) turns all kinds of waste into rich fertiliser (even eco-nappies, as shown by award-winning Young Scientists). Their castings, much analysed, are packed with busy bacteria, processing minerals for plant food.

The benevolence of earthworms is more usually brought to mind by a spadeful of soil with gesticulating species more like the one in my drawing. (I bury them quickly again, before a robin can nip in.) Lumbricus terrestris is our biggest garden earthworm, but the family of Lumbricidae numbers a couple of dozen Irish species. Many more, from other worm groups, live in woodlands, bogs and dunes. All are great nutrient cyclers, but burrowing garden worms also improve the structure of the soil. Their network of tunnels opens it up to air and moisture, and their mucus helps to create soil crumbs, leaving spaces for the rest of the earth’s teeming underworld.

Charles Darwin may be the best-known pioneer of earthworm research, in his book The Formation of Vegetable Mould Through the Actions of Worms (1881), but another naturalist, Gilbert White, was a full century ahead of him in detailed credit for earthworm activity. “Men,” he wrote in 1777, “would find that the earth without worms would soon become cold, hard-bound and void of fermentation.” Science has moved on, but its conclusion hasn’t changed. In 2008 the Environmental Protection Agency noted that the top 30cm of a hectare of soil contains up to 25 tonnes of interacting soil organisms, a biological diversity far exceeding that above the surface: worms, beetles, springtails, mites, spiders, ants, nematodes, fungi and bacteria help the soil to support “all life on earth”.

At the surface life can be far from earthworm-friendly. Along with blackbirds, foxes and badgers are new and voracious predators: Antipodean flatworms, coiled up under stones or flowerpots and roaming out to envelop earthworms as food. It’s some 40 years since the New Zealand flatworm, Arthurdendyus triangulatus, arrived in Belfast with imported plants, spreading rapidly across Northern Ireland and into the Republic.

Arthurdendyus (originally Artioposthia triangulata) is flat, sticky and pointed at both ends, purple-brown on top with pale yellow margins, about 1cm wide by 6cm long, longer if it’s moving. Its egg capsules look like blackcurrants. Another predatory flatworm, Australoplana sanguinea, already reported twice to “Eye on nature” from gardens in Co Dublin, is smaller and varies from cream or white to peachy-pink, often with a red tinge near the head. Stamp on either, or drop into salty water.

When the New Zealand flatworm’s expansion first came to notice, in the late 1980s, one scientist conducting field experiments saw it as “a severe threat to the earthworm populations of Northern Ireland”. In Scotland, where the planarian (the flatworm’s scientific category) is also well established, some studies have found a 12 per cent reduction in earthworms.

Noting this in 2008, the EPA looked in vain for any comparable national research in the Republic. Various grassland studies have found no significant shortage of earthworms, especially when given ploughed-in barley straw to chew on, but the EPA is funding a study of soil biodiversity by three universities, plus Teagasc, that may yield some incidental idea of the planarian’s advance. In Scotland the flatworm’s spread has been slow, in company with perhaps a dozen other alien planarians introduced through the plant trade.

An influential “rule of 10s” has been suggested by the British ecologists Mark Williamson and Alastair Fitter, who reckon that about 10 per cent of imported alien species appear in the wild, 10 per cent will establish self-sustaining populations and 10 per cent of established species become pestiferous. The example of Arthurdendyus has been judged to fit the rule, but its pestiferousness in Ireland could prove at least 10 times too much.

Eye on nature

As I walked up Mount Eagle, on Dingle Peninsula, plenty of frogspawn was in evidence. As we went up the mountain, cloudiness became apparent within the structure of the spawn. Eventually, at about 200m, it appeared desiccated and cloudy and without any tadpoles.Mike O'Connor, Millstreet, Co Cork

Frogspawn is often killed by frost, diseases and drying out. This sounds like frost or drying out.

I have about 40 frogs competing to fertilise the spawn in my pond, but one seems to have got mixed up and grabbed a healthy, bright-orange goldfish, presumably thinking it was a female frog.Bob Quinn, Bealadangan, Co Galway

There has been much frog activity at Glenagimla, on the south side of Killary, in mid February. Is the female frog more colourful at this time to attract males? Eoin Garrett, Knocklyon, Dublin, 16

Female frogs tend to be more brightly marked, but so do some males. I find no suggestion that it has anything to do with breeding.

We have had a hen harrier in our garden being harried by crows and magpies.Ann and Frank Turpin, Percy Place, D4

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or e-mail viney@anu.ie. Please include a postal address