Those snails!!!!

[stilllovingmysleep]

The little blighters (=snails) have munched up my poor hydrangea which is even in a big pot in the front garden. I keep finding them everywhere. How can I deter them? Help!!

[foresttrees2]

Stilllovingsleep I would just put the bowl wherever is convenient, maybe near the pot. It should attract them from nearby, but I don't know the actual range!
Going to check all the slug pellets in the shed now, it had never really occurred to me about the long term environmental impact

[shovetheholly]

I really really wish I could believe that metaldehyde does little harm pigletjohn. Accidentally killing that hedgehog is one of the worst things I have ever done and the fact that it was connected with gardening, which is something I love, is just horrible. I would dearly, dearly like to believe it wasn't my fault!

However, your questions have made me look into this in more detail, and I've learned a lot just on the relatively cursory glance I've given it as a total non-expert who has no business doing such things (I do wish we had a vet to consult!)

One thing I’ve learned is that the conclusions you have to draw on metaldehyde are more complicated than my past position of ‘it’s just lethal’ has been. It’s by no means as bad as the banned pesticide methiocarb, for instance.

The other thing I've noticed is that a lot of people seem focused on toxicology, and a lot of the reports are about the ingestion of large amounts of poison. Obviously, lethal dose matters: none of us want to see wildlife dying. But there may be all kinds of biological effects that are sub-lethal with injestion of metaldehyde, and these seem to be virtually unresearched.

I think the most shocking thing to me is just how little evidence there is out there. It seems that people have fed this chemical to various animals to determine the LD50 (where 50% of them die), but that’s about it. I don't mean to make a point that metaldehyde is safe or that it is dangerous. I mean that there seem to be huge gaps in our knowledge of how it affects different kinds of organism, particularly at sublethal levels.

Things I have found out:

• There seems to be a consensus amongst scientists and the water industry that it definitely does cause water pollution - and it can't easily be removed from our drinking water. Levels in some areas of the country have been reported that way exceed EU recommendations. Concern about this amongst water companies seems to be leading to a lot of cooperative efforts with farmers, yet levels seem to be getting worse not better.
  

Kay and Grayson 'Using water industry data to assess the metaldehyde pollution problem' Water and Environment Journal, Volume 28, Issue 3, pages 410–417, September 2014

• Once it gets into the water, metaldehyde affects aquatic ecosystems (which are full of molluscs), though different organisms seem to be affected in different ways, and bioaccumulation does not apppear to occur. Fish are affected, though it's not extremely toxic to them - a study of a rice paddy ecosystem found that a proportion of carp, tilapia died on metaldehyde applications to the field.
  

Moreau et al 'In vivo effects of metaldehyde on Pacific oyster, Crassostrea gigas: comparing hemocyte parameters in two oyster families' Crop Protection: Environment, Human Health, And Biodiversity, Environmental Science and Pollution Research, June 2015, Volume 22, Issue 11, pp 8003-8009

Calumpang et at 'Environmental Impact of Two Molluscicides: Niclosamide and Metaldehyde in a Rice Paddy Ecosystem', Bull. Environ. Contam. Toxicol. (1995) 55:494--501

• Terrestrial organisms are also affected:
  

It doesn’t seem to kill earthworms:
Edwards et al ‘The relative toxicity of metaldehyde and iron phosphate-based molluscicides to earthworms’, Crop Protection, Volume 28, Issue 4, April 2009, Pages 289–294

• There seems to be disagreement on the effect on rats and mice, with some studies finding no lethal toxic effects, while others find evidence of toxicity - 'In one study 3 out of 17 and in the second study 2 out of 6 mortalities could be Metarex [metaldehyde] related (residues found in respective carcasses): www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/1856.pdf p 54.
  

There is evidence that metaldehyde disrupts the physiology of these creatures at a sub-lethal level. One study found significant problems with the spinal cords of rats at higher doses.
Vershuuren et al ‘Long-term toxicity and reproduction studies with metaldehyde in rats’ Toxicology
Volume 4, Issue 1, 1975, Pages 97-115.

Sparks et al ‘Metaldehyde Molluscicide Action in Mice: Distribution, Metabolism, and Possible Relation to GABAergic System’ Pesticide Biochemistry and Physiology, Volume 55, Issue 3, July 1996, Pages 226–236

• Slug-eating mammals like hedgehogs are less affected. (Maybe I didn’t kill that hedgehog after all!) High doses are believed to be needed for poisoning. However, there are cases where toxicology reports show metaldehyde poisoning. However, a study of mortality in British hedgehogs found 3 animals who were suspected to have died of metaldehyde poisoning:
  

Keymer et al ‘Zoonoses and other findings in hedgehogs (Erinaceus europaeus): a survey of mortality and review of the literature.’ Vet Rec. 1991 Mar 16;128(11):245-9.

Birds are also affected

-While herbivorous birds seem to avoid metaldehyde after a certain dose, there is a 'high acute and long-term risk' to grain-feeding birds who eat the granules. www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/1856.pdf

Aside from this, a study of the effect of metaldehyde in ducks suggests it can be linked to ‘reductions in the ratios of number hatched to eggs laid, to eggs set, and to live embryos and reduction in the ratio of hatchling survival to eggs set’. toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+173

I am sure a real expert/toxicologist would be able to provide far more evidence than I have done here. I think my overall conclusion is: it's not the devil I thought, but I will definitely not be using it any time soon either! For me just personally and based on my very non-expert look at a few articles, Twycross Zoo’s report on metaldehyde seems right to conclude that it’s a lot safer than some other pesticides but that ‘This is not to say that metaldehyde is without negative effects, and every encouragement should be given to domestic users to find alternative, non-chemical means to protect their plants.’ wildpro.twycrosszoo.org/S/00Ref/MiscellaneousContents/D86HedgMolluscicide/D86_3_The_Molluscicides.htm#3.1.1

[LetThereBeCupcakes]

If you use beer they will be deceased, though remember theyvdied happy. I think you can poor the beer/slug/snail soup on the compost heap? Shove or Zebra will know.

[user1464020114]

Someone told me coco shells are good but only if you don't have dogs

[stilllovingmysleep]

(meant: should I put the little bowl of beer in the flower pot?)

[stilllovingmysleep]

by the way should I put the little pot of beer in the actual pot? It's a relatively big pot with an hydrangea in (with all its beautiful flowers & leaves munched on. I don't know how on earth those stupid snails manage to get up there as it's placed on 4 little terracotta thingies so off the ground. They are clever!!!

I love the idea of using my 7 year old DS as a slug/snail catcher by the way! It may satisfy his bloodthirsty nature.

Last question: what do you do with the snails once you catch them? So far I confess I have been throwing them angrily on the little path in front of my house (=my own bloodthirsty nature in action) but are there more (ahem) humane solutions?

[stilllovingmysleep]

not sure whether my own snails are posh or working class but I'll try different beer at different levels of poshness & will report back to you!

For safety I have brought indoors (to my conservatory) all other tender / green / grown from seed potted plants & they seem happy enough there. I will be using more woody plants I think for my pots in front garden from now on.

[IrenetheQuaint]

[TheSpottedZebra]

See, Irene, your slugs probably don't do yeast and wanted an artisan sourdough starter.

[LetThereBeCupcakes]

They'll be demanding malt whisky soon.

[IrenetheQuaint]

I fear as much, Cupcakes :( I tried yeast and sugar a couple of times as mentioned by Zebra and the slugs were like

I live in an "up-and-coming" bit of London and am worried that the sudden preponderance of naice delis and pubs serving craft ale is giving them ideas.

[LetThereBeCupcakes]

Irene do you think our slugs might be a bit...you know...snobbish?

[IrenetheQuaint]

My slugs love Guinness, but it's expensive so they only get it if I've been cooking with some. Another sort of stout someone gave me once worked well, too.

Unfortunately they turn their little antennae up at Sainsbury's Economy Bitter :(

[TheSpottedZebra]

Your slugs are posher than mine, as I do use value brands! I used the ale one, not the lager.
But I'm sure that I read that you can just use a bit of yeast and sugar in water and that does the same job?

[LetThereBeCupcakes]

Spotted what beer do you use? I tried a couple of different "value" brands and the slugs wouldn't touch it!! If my Dad knew I was giving them the good stuff I think he'd have a heart attack...

[TheSpottedZebra]

I'm another who avoids metaldeyde pellets, hut uses the ferric phosphate ones sparingly.

OP, in addition to all the barrier methods mentioned, do you have a young child you could train up to catch slugs and snails? I have a 7yo, he has been catching 'chompers' for me for 2 years now. I pay him based on how many he catches He is small and flexible and bloodthirsty and can get into nooks and crannies.

I sometimes do beer traps too - cheapest beer is fine. But leave a small lip of the trap (yogurt pot, whatever), sticking up from the soil so that stuff you do want, like beetles, don't fall in.

[PigletJohn]

holly

Your document says "several cases of poisoning have
been reported where animals have had access to large quantities of the formulation"

Surely this means where they have eaten it from a storage bin? Not where they have found a few dozen pellets scattered on a flowerbed?

[derektheladyhamster]

I have a lot of snails. After living here for 20 years, I've given up. I've learnt which plants they leave alone and I only plant them. It doesn't make for a fabulous garden, but I've never found anything which irradcates them

[LetThereBeCupcakes]

Beer traps have been most effective for me. You can buy them, I think, but I make my own. I just sink a dish into the ground and fill with alcohol (old speckled hen been the most effective so far!). I cover with a roof tile to stop my dogs drinking it (trust me, drunk labs are NOT fun to be around).

It's sickening, isn't it? Last year they stripped FOUR lots of runner bean plants.

[shovetheholly]

The fact that those two last peer-reviewed sources suggest that some hedgehogs are dying of metaldehyde poisoning suggests to me that it possible for certain of these animals to eat enough of the chemical to reach a lethal dose! (Info on the test here: www.sciencedirect.com/science/article/pii/S0021967301876196 )

Why might this be the case? Maybe the the toxicity levels have been wrongly calculated and are lower than suggested, or maybe some kind of accumulation is happening (though this seems unlikely given the short half-life), or maybe another factor is in play, e.g. exposure to a second chemical of some kind that intensifies the effects?

My question is: since there is credible evidence to suggest that metaldehyde HAS killed some hedgehogs, even if we don't understand the mechanisms of this exactly yet - and we do have alternative methods - then isn't it safer to set beer traps or use nematodes?

All documents suggest that lower doses may be lethal to other mammals (e.g. wood mice) and birds, so it's not just hedgehogs either.

[IrenetheQuaint]

Just put the beer trap in the ground near the relevant plants. I chuck a few organic slug pellets in too (tend to avoid metaldehyde but interested that PigletJohn's research suggests it may be OK for wildlife if scattered thinly).

[stilllovingmysleep]

Thanks foresttrees; and put the beer trap where?

[foresttrees2]

To make a beer trap, pour some beer in a bowl with a piece of fruit in it.

[PigletJohn]

Thanks for the link, holly. I am fond of hedgehogs and other wildlife and have been searching your document to see what evidence it cites for danger. Can you see it? I can't.

I see the part that says

"The agreed Acceptable Daily Intake (ADI) is 0.02 mg/kg bw/day based on the 2-year rat study, the Acceptable Operator Exposure Level (AOEL) is 0.1 mg/kg bw/day based on the 52-week dog study,and the Acute Reference Dose (ARfD) is 0.3 mg/kg bw based on the acute neurological findings observed from the first week of the 52-week dog study. All reference values were derived with the use of a safety factor of 100"

however I haven't yet found how many pellets you would need to eat every day for two years to reach the Acceptable Daily Intake. The agricultural bait tested contained 50g metaldehyde per kg, but I understand amateur products usually contain about 3%, but I don't know the weight of a mini-pellet.


I did find this other document which says " a 1kg hedgehog would have to directly ingest 490 pellets " and " A study by Gemmeke (1999) showed that metaldehyde pellets were least preferred by hedgehogs when given a choice between methiocarb, thiodicarb and metaldehyde, and over 2800 slugs would need to be consumed to achieve LD50 toxicity levels (based on rat LD50). Gemmeke (1995) also reported that hedgehogs would eat (dead) contaminated slugs – up to 200 in one night – with no apparent side effects."

I have not yet decided the significance of these figures. I typically scatter several dozen mini-pellets a week.

[shovetheholly]

And to add a completely non-scientific, anecdotal piece of testimony: I should add that years ago, I used to be a metaldehyde pellet user. Then one morning I found a hedgehog convulsing on my lawn. It died in agony, frothing at the mouth with a blue-tinged foam. I have always believed that I was to blame for killing it and I will never, ever use the pellets again. It is a shame that it took the death of a lovely little creature to make me change my ways.