Raspers

I have a greenhouse and this week it was time to put some shading on the glass to stop the plants frying in the strong spring sunlight. I do this every year but usually with a proprietary brand of paint-on shading I get from the local garden centre. Not wanting to sortie to the nursery shop under the “stay at home” lockdown, I resorted to an old method I used to use in much younger days when garden centres were not even a glint in a commercial horticulturalist’s eye. This involves mixing a runny paste of flour and water and using that. You have to start with a small amount and then gradually increase the mix to avoid lumps (or more lazily, pour the flour and water in together and then borrow the kitchen whisk).  

I completed the task and painted the glass with the floury paste and it dried nicely to a white sun shield. Next morning, though, lots of rather attractive spiky patterns and trails appeared. This, I recalled from my youth, had happened before. The culprits? Snails. These voracious omnivores sensed a meal and busily scraped off the dried flour, using a microscopically toothy organ called a radula, and it is that which leaves these attractive patterns, large and small, depending on the size of the rasping perpetrator. The Natural History Museum has an excellent illustrated explanation at https://nhm.org/stories/microscopic-look-snail-jaws. Well worth a read. The inset in my photo is an enlargement of a section of a trail.

As for me, I shall have to re-flour my glass every so often and hope the gastropods stay outside rather than venture through the ventilators onto the juicy plants they might spy inside!