Context: my mum does not have a garden of her own and lives 10 minutes away. We do have a garden but aren't desperately interested in gardening. So she grows stuff in our garden for us. It is a compromise which would suit everyone except that she insists on growing plants which snails like to eat. Having been a gardener for decades, my mum thinks that snails are ravenous monsters who must be squashed like bugs. Richard and I are woolly hippies who object to killing things, and rather like snails.
Currently, we are checking the plant pots in the front garden (neat, pretty flowers). If a snail is found, we carry it through the house to the wild back garden, which contains a buddleia triffid (snails can eat what they want). However, there is a certain amount of hassle involved in this and I would like to prevent the snails from getting to the plants in the first place. Prevention is better than cure.
My plan is to shield the plants that we care about with copper and then have some sacrificial plants for the snails to eat. Apparently snails can't/won't cross copper, so I wanted to find out why. Copper salts are generally toxic to living organisms and gastropods have osmotically permeable undersides - fluffymormegil says this is why ships traditionally had copper-plated hulls to keep barnacles off. But it's also well known that shielding plants with copper doesn't harm the snails. Another point is that molluscs have blood with haemocyanin as their oxygen carrier instead of haemoglobin. Haemocyanin has two copper ions in the middle of it instead of one iron ion, so I wondered if that could be relevant.
Anyway, it turns out to be a question that is not yet properly answered by science. Lots of websites blindly declare that copper creates a mild electric discharge which snails learn to avoid, and some even ascribe this to the snail or slug slime combining with the copper barrier to create an electrolytic effect. The weird thing is that even oxidised copper that's turned green (formed copper (II) carbonate) will still work, and if direct electrical contact was necessary it wouldn't work, as solid salts do not conduct. This study suggests that copper(II) ions block calcium(II)-activated cationic channels in the snails' neurones, and so the electric shock felt is inside the snail itself. (Thanks to Yaakov on Freenode for finding it for me.)
However, that paper is based on the prior knowledge that snails won't cross copper. It doesn't answer whether copper is the only metal that snails won't cross. I was imagining that aluminium would be irrelevant to them because the oxide layer prevents further reactions, but they are still affected by copper with a carbonate layer. So now I'm wondering whether it's the electrode potential or the size of the metal cation that causes the neurone screwup. I need to do a citation index search and see if anything has come up more recently. I'm also tempted to try several different metals of similar reactivity and do some sort of experiment.
HoopyCat's comment about this idea: #soc.bi science fair!
Random other HoopyCat gems from today:
<HoopyCat> being-the-middleman guideline #3: when relaying messages between two people who are geeking out on a topic that's well outside your normal geeking range, put them in direct contact; it will probably result in something cool.
<astra> in our sainsbury's, next to the vegan bouillon, they have CANS of SNAILS
<HoopyCat> canned snail! they keep that next to the potted meat food product here.
<astra> and i always thought it was a special variety of snail that was eaten, but these ones look JUST LIKE the ones in our garden :(
<HoopyCat> i wish to believe that a lot of these items were originally made into canned goods while our world in the depths of the cold war
<HoopyCat> in your fallout shelter, keep canned snails and potted meat on the visible shelves... when your neighbors come over for the tour, they see your canned goods consist of utterly unappealing crap and then decide to build their own fallout shelter
<astra> i like snails
<HoopyCat> 'course, in the event of REAL emergency, you have shelves of good stuff behind a fake wall
<astra> i should do some revision :/
<astra> the book's been open on my desk for hours, but i've had a head full of snails (among other things).
* astra wonders if "head full of snails" is going to become her new reason why she couldn't get something done
<astra> "sorry, i tried to look that up online for you, but i had a head full of snails and forgot about everything that wasn't a mollusc."
<HoopyCat> old and busted: no spoons new hotness: head full of snails