Slugfest

Arion rufus ¼ adult (probably) feeding on flower
Arion rufus ¼ adult (probably) feeding on flower

No, it’s not a MMA slugging match but a wet day in Scarborough! Slugs (and snails) love a damp summer day, with a shower or two to keep the vegetation moist so they can glide around the garden!

Common Garden Slug (Arion distinctus) side view showing mantle, and stripy skirt running along the bottom of the foot
Common Garden Slug (Arion distinctus) side view showing mantle, and stripy skirt running along the bottom of the foot

Here (below) are a group of slugs feeding on fallen leaves; they almost look like they are at a food bar! Notice the tiny little grey-black sluglet – not the small one on the left – below the third slug at the bottom of the image. So these slugs are doing something useful – helping me tidy up fallen leaves! They also feed on a wide range of rotting organic matter, processing it through their bodies and enriching the soil.

Slugs feeding

OK they do feed on garden plants and flowers (!) although that has never bothered me. Here (below) is one feeding on a yellow poppy. You can see the slug’s mouth (radula) through the flower.

Common Garden Slug (Arion distinctus) feeding on yellow poppy flower
Common Garden Slug (Arion distinctus) feeding on yellow poppy flower

This particular Garden slug (next three images) was very acrobatic, hanging onto the end of a stem and moving about trying to locate another flower to feed on.

Common Garden Slug (Arion distinctus) hanging from stem
Common Garden Slug (Arion distinctus) hanging from stem

There are two tiny dots of reflected light on the two optical tentacles: the light-sensitive eye-spots. What did I look like to the slug?

Garden slug optical tentacles with eye-spots
Garden slug optical tentacles with eye-spots

Here is another shot (below) showing both the optical and sensory tentacles as the animal searches for another plant. The fluidity of its movement is amazing; all whilst holding onto the end of a tiny flower stalk.

Garden slug showing optical and sensory tentacles
Garden slug showing optical and sensory tentacles

All that action needs energy and like us they need to breathe. Slugs take in air through a hole in their mantle called a pneumostome. The sides of this ‘blow-hole’ appear blue in this garden slug (below). They are also said to have green blood.

Common Garden Slug (Arion distinctus) with pneumostome
Common Garden Slug (Arion distinctus) with pneumostome

There is a lot more to say about slugs – such as how they move, their mucus, their hermaphroditic sex life and so on – but for now, I am pleased to have had a damp day on which to appreciate these amazing animals.

Mollusc musings

White-lipped snail feeding on gorse
White-lipped snail feeding on gorse

“It’s a lovely day” said the snail.

“Yes” said the slug. “It’s been raining all day and everything is damp and wet”!

European black slug (Arion ater) on moss_edited-1

“I think I’ll slide off for a bite to eat” said the snail.

White-lipped snail feeding on gorse
White-lipped snail feeding on gorse

“Watch you don’t slip up” giggled the slug. “With that shell and all”!

European black slug (Arion ater)
European black slug (Arion ater)

“What’s the forecast?” said the snail.

“Brilliant; rain all week” said the slug. “Enjoy it while it lasts!”

All images were taken in Galicia, Spain, where it often rains!

 

 

Citizen snail

Grove snail (Cepea nemoralis) one-banded, yellow form from Galicia, Spain
Grove snail (Cepea nemoralis) one-banded, yellow form from Galicia, Spain

An enormous amount of work has been carried out over the years to try to understand the genetics of this little snail; the brown-lipped banded snail (Cepaea nemoralis). It has been called a model organism, and has been the subject of a huge citizen science project. So lets call it citizen snail! It is highly variable, and exists in a number of different forms, with different colours (yellow, pink and brown) and different numbers of dark bands (none, one or many). Researchers have tried to understand what influences the distribution of these polymorphisms. For example, are they determined by selection pressure (such as predation by thrushes), changes in the environment like temperature, or just genetic drift. Drifting lazily from one form to the other as the lords of randomness decree!

Recently, this obliging little snail found itself the focus of a huge effort of citizen science, to see whether it had changed over the last 40-50 years as a result of climate change (1). The question was: have recent increases in temperature ‘favoured shell morphs with a higher albedo’ (1). In other words, if its getting hotter, will the snail adapt to have lighter coloured yellow shells which reflect back more of the sunlight they receive? A bit like changing to a lighter coloured umbrella!

Participants were instructed on: i) how to find (‘hunt for’) snails, ii) how to distinguish C. nemoralis from a closely related species (C. hortensis), and iii) how to separate adults from juveniles (2). In total, over half a million snails were sampled (1). They weren’t killed, they were all put back after being examined. The results of this Evolution MegaLab project were impressive, with nearly 3,000 new records on polymorphism obtained from 15 European countries (3). In the end, it turned out that ‘there was no general increase in the frequency of yellow shells’, perhaps because the snails can always slide off into the shade if they get too hot! But the work did show an increase in the frequency of banded shell forms, perhaps – it was speculated – because of ‘changing predation pressure by birds’ (1). So they might be the subject of another study to see what birds are eating them! Perhaps we should warn them to prepared for another snail hunt!

1. Silvertown, Jonathan, et al. “Citizen science reveals unexpected continental-scale evolutionary change in a model organism.” PLoS One 6.4 (2011): e18927.

2. http://www.evolutionmegalab.org/file_downloads/en/How_to_hunt_banded_snails.pdf

3. Worthington, Jenny P., et al. “Evolution MegaLab: a case study in citizen science methods.” Methods in Ecology and Evolution 3.2 (2012): 303-309.