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SLUGS AND SNAILS probably tempt more organic gardeners from the true
path than any other pest. But the Henry Doubleday Research Association (HDRA),
based near Coventry in the Midlands, is working hard to come up with improved,
and safe, methods of control.

The problem with methiocarb and metaldehyde, the two most common slug-killing
chemicals, is that they are not as bad for slugs as they seem (see main
text), and can also harm other wildlife, including pets.

Birds, hedgehogs and toads, all of which eat slugs and snails, can accumulate
the poisons that have made their prey more vulnerable. Methiocarb also kills
worms, insects and rodents, and it may actually increase the slug problem
by laying waste to beneficial animals, such as ground beetles. And dogs,
which have no effect on slugs either way, seem attracted to metaldehyde
pellets, often with fatal consequences.

So what are the alternatives? One is to create a barrier around vulnerable
plants. The idea is to surround the plant with something that slugs prefer
not to crawl over, perhaps because it is an irritant or overtaxes their
slime glands. Crushed egg shells, shredded bark, sharp sand, wood ash and
short hair clippings all have their advocates, but all lose their efficacy
when they become wet.

By far the best anti-slug barrier is a mini-cloche, made from an empty
plastic soft-drink bottle with the bottom cut off. This will keep slugs
away from young seedlings, and can be removed when the plant is large enough,
or left in place if the seedling is a climbing bean that has emerged through
the top of the bottle. ‘The only drawback of this method,’ says the HDRA,
‘is if a slug is inadvertently trapped inside the mini-cloche.’ I can vouch
for that.

Many gardeners swear by traps, that is, saucers or tubs sunk into the
ground and filled with beer or milk. Slugs are attracted to the bait, fall
in, and drown. The HDRA says that such traps will have an effect only at
very high densities, at least one per square metre. ‘They are unlikely to
have any great effect on the overall slug population, but a trap full of
dead slugs can be a great morale booster to the beleaguered gardener.’ But
traps also catch beneficial ground beetles, and so may do more harm than
good. To get around this, the HDRA recommends traps whose edge is 2 centimetres
above the soil; ‘slugs will still climb in, but beetles should not be able
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A different approach is to encourage natural predators. Hedgehogs eat
vast numbers of slugs each night. Frogs and toads are also partial to slugs,
which may form a quarter of their diet. In the past wise gardeners kept
a toad or two in the greenhouse specifically to keep down slugs, and although
amphibians will also eat beneficial insects, such as ground beetles, on
balance they probably do more good than harm.

Birds too, especially song thrushes and redwings, are famous for smashing
snail shells on anvils to get at the animal inside, but they also eat slugs,
as do many other birds. Ducks are particularly good at slug control, and
many commercial organic gardeners keep a flock. But perhaps the most promising
predators of slugs are ground beetles.

Many carabid and staphilinid beetles are voracious hunters who include
slugs and the larvae of insect pests in their diet. Unfortunately, the beetles
breed slowly, and under normal circumstances there are not enough of them
to keep slugs under control. The HDRA has funded research by William Symondson,
at the University of Wales in Cardiff, to devise ways of increasing the
number of predatory beetles around vulnerable plants.

One is the pitfall plot. This is a normal garden bed, edged with smooth
plastic so that there is a cliff at least 4 centimetres high facing the
crops. The beetles wander at random looking for food, and any that fall
over the edge of the cliff will not be able to escape. Thus the number of
beetles within the pitfall plot increases to a level where they can cope
with the slugs.

Symondson is now moving on to develop the most efficient predator, a
beetle called Abax parallelepipdus, into a suitable agent for biological
control. He is concentrating on breeding techniques that will enable the
beetles to be produced in sufficient numbers for them to be cheaply available
to stock pitfall plots.

In the meantime, I recommend nightly forays with a torch and an empty
jar, with lid. It is astonishing how many slugs and snails you can collect
in a few minutes, and extremely satisfying to spread them on the lawn for
the birds next morning. Whether it has any effect on the overall population
of slugs, I cannot yet say. But I am counting.