Summer of the Slug

Lilies smallHas there ever been a ‘summer’ (and that’s another problem, of course…) like this for slugs? I suppose it’s the combination of a mild winter (only one day on which the car windscreen was frosted, and no snow at all) and a wet spring and early summer that has caused the little nuisances to survive, and to multiply unchecked. I’m disgusted at the failure of the birds I so lovingly feed to make any effort to help with the problem, and am thinking of putting myself on a waiting list for rehoming a rescue hedgehog (too differently abled to be released back into the wild). A friend has a blind one in her garden, and you should see her untouched hostas …  

My latest printing acquisition – not much use in the present crisis, though.

My latest printing acquisition – not much use in the present crisis, though.

A few weeks ago, after a succession of rainy evenings, when the annoying little things (I hope you are noticing the restraint of my language) were gliding across my not very smooth paving like the Bolshoi Ballet on ice, the iron entered my soul: I tipped a large amount of salt into a bucket, pulled on a pair of latex gloves, and sallied forth.

Fifteen minutes later, I had forty or so, making unpleasant wheezing noises in the bucket, but still they came: all sizes and colours, all over everything, including plants like tomatoes and hardy geraniums which they would never normally touch. Some were climbing vertically up the glass of the French windows, a long way from any greenery: others were making for the sweet pea seedlings, which, for a variety of reasons have been a complete non-event-style disaster this year; pinks, iris, cosmos, nicotiana, tagetes, you name it …

Autumn-sown sweet peas, a complete failure (they're coming out this afternoon).

Autumn-sown sweet peas, a complete failure (they’re coming out this afternoon).

I have previously tried copper tape (they cross it), eggshells, coffee grounds, alpine grit and sharp sand (they ignore them all), and mini-cloches of cut-down plastic bottles (they are not deterred by the sharp edges). I haven’t had a go at nematodes (and so far this year I rather doubt if the soil has been warm enough for them). But I have a guilty confession: I have used the dreaded blue pellets, though only in my (raised) cold frame and plastic ‘greenhouse’, where I am confident birds and Max the Cat don’t go.

Slug damage on Hemerocallis (the flowers are always sabotaged by hemerocallis gall midge fly anyway...).

Slug damage on Hemerocallis (the flowers are always sabotaged by hemerocallis gall midge fly anyway…).

Seeking online for suggestions, I found an upbeat website with many suggestions, some more plausible-sounding than others. One tip is to cause the pests to gorge themselves into helpless immobility by laying oatmeal and bran round all the plants; and, among other useful facts, I learned that slug slime is hygroscopic, i.e. it absorbs moisture, which increases the volume of slime. This is why they can move so much faster in wet weather, and also why it is so difficult to wash the slime off your hands: it just keeps expanding. We are advised to rub our dry hands together until the slime forms small balls (sounds like making pastry) which we can pick off and dispose, and then wash our hands.

Lily flowers eaten out (as though the lily beetles were not enough to contend with).

Lily flowers eaten out (as though the lily beetles were not enough to contend with).

One thing did worked: I got my ancient plastic beer trap out of the shed. It had never trapped a thing when I used to buy the cheapest possible stuff to bait it with (I don’t drink beer, and Him Indoors has rarefied taste in this respect), but at the moment we have proper Belgian beer in the house in to help Him through the various crises of the European Cup, and, lo, the slugs really went for it (something to do with the high sugar level). However, it’s an expensive pastime, though I suppose they die happier in beer than in salt.

The beer trap. I haven't used it for the last few days, and when I took the lid off to photograph it, a nest of earwigs was revealed...

The beer trap. I haven’t used it for the last few days, and when I took the lid off to photograph it, a nest of earwigs was revealed…

So, what are these strange and well-adapted beasts with a weakness for beer? You can find information and a whole range of images on the Slugwatch website. (I haven’t put any pictures of slugs in this piece because they don’t deserve the oxygen of publicity.) Linnaeus must have been having a poetic moment when in 1758 he decided to call the genus ‘Arion’, after the Greek singer saved from drowning by a friendly dolphin – or was he thinking of the way that the critters glide along on their slime as on the crest of a wave?

The famous mosaic centre-piece of a winged boy on a dolphin, from the Roman palace at Fishbourne.

The famous mosaic centre-piece of a winged boy on a dolphin, from the Roman palace at Fishbourne.

There are two invasive species in the UK at the moment, the Spanish Slug (Arion vulgaris) and the even more sinister-sounding (and difficult to pronounce) Spanish Stealth Slug (Arion flagellus). The latter has been here since 1945 or so, but the former is a more recent arrival (probably on imported nursery plants), and Slugwatch gives a depressing list of its unattractive traits: breeds twice as fast as natives, eats plants that natives won’t normally touch, tolerates hot, dry summers (not that that is an immediate problem…).

The most spectacular is probably the Large Black Slug and its Large Red alter ego (Arion ater and Arion rufus respectively). I saw some black ones recently at the side of a meadow full of bee orchids, and observed them curling into a ball when disturbed, though not rocking from side to side as they are alleged to do. Slugwatch also says that ‘this species of slug will sometimes eat seedlings on agricultural land’. You think?

Bee orchids in Suffolk: I didn't photograph the slugs ...

Bee orchids in Suffolk: I didn’t photograph the slugs …

One of them is not unattractive (she said grudgingly): the Brown-Banded Arion (Arion circumscriptus) has an attractive iridescent sheen – but so of course does the beautiful but deadly rosemary beetle, another unintended consequence of importing plants –currently spreading inexorably up the country and destroying lavender and rosemary plants in its wake.

The spectacular but evil rosemary beetle.

The spectacular but evil rosemary beetle.

I had a quick look at some nineteenth-century slug-related advice to gardeners: poisoning was a popular option. Eliza Kent, in Flora domestica (1823) deals with any pests by watering with ‘tobacco-water, which quickly destroys them. … One pound of roll-tobacco will suffice for three pints of water, which should be poured on it nearly boiling, and stand a few hours before it is used’. Some claim that, in addition, this treatment ‘improves the verdure of the plants’.

Get your pound of roll-tobacco here.

Get your pound of roll-tobacco here.

The great J.C. Loudon, in his 1828 Green-House Companion, advises: ‘hand-pick them [slugs] in the early morning, when it is hardly light; or strew over the floor of the greenhouse … leaves of any of the cabbage tribe just beginning to decay.’ Startlingly, he also urges the destruction of earthworms in the pots, ‘by watering with any bitter, acrid, or acid infusion or solution, as of water of walnut leaves or tobacco, or salt-water, lime-water or vinegar’. Tobacco plants can be grown specifically to make a poison.

Nicotiana mutabilis, after hammering by slugs and a freak hailstorm.

Nicotiana mutabilis, after hammering by slugs and a freak hailstorm. Not much use as a source of pesticide …

For outdoors, in the second (posthumous) edition (1850) of The Suburban Gardener and Villa Companion (1838), Loudon says that ‘The most effectual mode, when they are in large quantities, is, to collect them by hand and then destroy them; and, when they are less numerous, to water every part of the garden thoroughly and repeatedly with clear lime water, which … effectually destroys snails, slugs, and worms’. (That earthworms were seen as pests on a par with slugs and snails is perhaps surprising, but Darwin’s summary of a lifetime’s observation of the value of earthworms in improving soil conditions for plant growth was not published until 1881.)

Samuel Beeton’s Book of Garden Management (1871) has (under ‘Pests of the garden’): ‘To destroy slugs … take fresh lime in a powdered state, put it in a coarse bag, and after night-fall or before sunrise, dust the ground where slugs are about: every slug touched with the smallest part of the lime will die at once.’ Strew cabbage leaves around, and any slugs escaping their doom will take shelter under them and can be disposed of at leisure. (I tried with with empty half-grapefruits and oranges, and it doesn’t work for me …)

By contrast with these diligent gentlemen, Miss Jekyll (in Wood and Garden, 1899) is positively smug: ‘But we have one grand consolation in having no slugs, at least hardly any that are truly indigenous; they do not like our dry, sandy heaths. Friends are very generous in sending them with plants, so that we have a moderate number that hang about frames and pot plants, though nothing much to boast of; but they never trouble seedlings in the open ground, and for this I can never be too thankful.’ This unexpected advantage of living in Surrey is, alas, not much use or consolation to the rest of us.

Caroline

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5 Responses to Summer of the Slug

  1. andgoldbug says:

    Nice blog, Professor!
    We could use your wet season. The dry spring here has led to a resurgence in Gypsy moth caterpillars that have defoliated swathes of the Northeast. The fungal pathogen that keeps them in check failed to materialize due to the dry conditions.

    Andrea G.
    Boston, MA

    Like

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