Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: chris on 18/06/2012 10:02:29
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I was asked by a listener this week about slug pellets and whether they cause the creatures a painful death. I approached the answer from the perspective of whether simple creatures like these can feel pain. But I would like to know how slug and snail pellets selectively poison these animals but are harmless to mammals. Does anyone know?
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I was asked by a listener this week about slug pellets and whether they cause the creatures a painful death.
Looks like Sluggy has fatal hangover ...
Typically it is applied in the form of slug pellets, which normally include a wheat bait. Metaldehyde acts on the pest by contact or ingestion, and the aqueous environment inside the pest's cells readily hydrolyzes metaldehyde into acetaldehyde, the molecule associated with an alcohol hangover.
https://en.wikipedia.org/wiki/Metaldehyde#As_a_pesticide
A hangover without alcohol seems unfair, give them a final drink ... http://www.thenakedscientists.com/forum/index.php?topic=34347.msg325620#msg325620
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Metaldehyde & methiocarb are the active ingredients in slug pellets. The former causes the slug to swell and the later cause’s damage to the mucus cells resulting in the over-production of mucus. Death is the result of dehydration.
Both these poisons are dangerous to other animals. Pellets are usually blue as this colour is not attractive to birds and the better quality pellets also have an animal repellent to prevent ingestion by non target animals. Some cheaper brands do not have this animal repellent.
However, even those with the animal repellent can and do result in direct poisoning of non target animals and indirect poisoning of non target animals is only too common. Dogs, cats and even horses have been known to ingest these pellets, causing anything from slight to severe illness and even death.
The pellets may be ingested accidentally by grazing or intentionally for the cereal based carrier. It is more often than not the case that these pellets are used in too high a quantity. They should be spread sparsely in order to kill the slugs, not densely, as many do. But they are mostly only shower proof and need to be replenished frequently in times of heavy or persistent rain. Run off can lead to poisoning of streams and ponds.
See this report in the Farmers Guardian (http://www.farmersguardian.com/metaldehyde-at-risk-if-leaching-into-watercourses-not-contained/23785.article).
In higher animals (including humans), these molluscicides can cause skin, eye and mucus membrane irritation by exposure to the vapour and dermatitis and conjunctivitis with long term or repeated exposure. Ingestion can cause kidney and liver damage severe abdominal pain, nausea, vomiting, diarrhoea, fever, convulsions, and coma. Other problems related to these poisons are increased heart rate, panting, asthma attack, depression, drowsiness, high blood pressure, inability to control the release of urine and faeces, incoordination, muscle tremors, sweating, excessive salivation, tearing, cyanosis, acidosis, stupor, and unconsciousness.
The biggest problem with slug pellets is their effect on wildlife. The dead or dying slug may become the prey of Hedgehogs, frogs, toads, birds etc. By taking a poisoned slug or snail, the predator inadvertently ingests the poison and may well suffer the consequences. The decline in the Hedgehog population in the UK has already been partly attributed to the ingestion of poisoned slugs and it is certain that other wild animals, frogs and toads in particular, are also suffering the same fate.
So how do we address the problem of slugs eating our prize plants? Whether you are growing plants for your delectations as a budding horticulturalist (I just had to get a pun in somewhere) or vegetables for your culinary delight, the last thing you want is to see them being decimated by the rasping lips of a huge slug. And the fact is, that this year has seen a giant leap in the number of slugs due to the inclement weather. Sadly, not so inclement if you happen to be a slug.
There are ways to protect your plants without the use of poisons. Spreading grit or stone chipping will discourage slugs, since they do like such surfaces. This also has the added bonus of being a good mulch, helping to retain water during hot dry weather (if we ever see such times again!). Copper bands are also used around plants. As the slug moves on to the copper, it gets a mild electric shock. Beer filled slug traps can be used to drown the slugs. (What a way to go!). You can also use rolled porridge oats as a deterrent.
Another means of defeating these pests is to employ nature itself. Make your garden Hedgehog friendly. A Hedgehog will consume slugs and snails and other garden pests such as earwigs. Set up a garden pond to attract frogs and toads and make birds such as Blackbirds and Thrushes welcome. Not only do you help solve your slug problem, but you also help wildlife.
But if you really are inundated with a plague of these pesky slime balls (Ooo, another pun) you can resort to nematoads. These tiny worm-like parasites attack slugs and slugs only, they are harmless to the soil, water and other animals. I must admit, we have decided to resort to this remedy with incredible results. While our neighbours are suffering from the attack of the slugs, we have yet to see one or any evidence of one in our garden since I applied them a few weeks ago.
I am most certainly impressed and you can take this as my endorsement of them. I will post a link to the site from which any interested party can obtain these nematoads if admin so allows and upon receipt of the mandatory brown envelope suitably stuffed with a great wad of dosh from the suppliers.
I might also add that you should be careful not to kill off all slugs, there are some predatory slugs which prey on other slugs.