Friday, May 14, 2010

Mollusc Hoodie



Most specimens of the large black slug Arion ater are jet black, but I found this handsome red form with grey tentacles crawling across a woodland path near Durham city today. The red form is much commoner in the south of England. In the image above you can see the large open breathing pore (pneumostome) that leads to the mantle cavity - a simple form of lung.


The whole slug was covered in a layer of grey mucus and ....



.... when fully extended was about 12 cm. long. This is our largest slug species.


Arion ater has very distinctive behaviour when you give it a prod. First it withdraws its tentacles under a hood and closes its pneumostome, then it gently rocks from side to side, as if in silent fury. This behaviour, combined with that distasteful mucus, probably deters a lot of predators.


After a while it will begin to extend an inquiring tentacle from under the hood, to see if the threat has gone and the coast is clear ...


.... and if it is it extends its tentacles, opens its pneumostome (to breathe a sigh of relief?) and glides away into the undergrowth.

17 comments:

  1. What a cracker of a slug! He's wonderful. I like the series of photos of the encounter. I'm now going to enlarge them to see him in all his glory. :D

    A few days ago I bought a miniature rose and there was a young tiger slug in the packaging. He's now living happily (I hope) on the inside lid of my compost bin.

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  2. Interesting Phil...I've never looked that closely at a Slug. Wonderful shots.

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  3. Great post with stupendous photos! I've never seen a slug that looked rough, though - this one almost looks like it has toothed scales on its back! Very cool.

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  4. Not my favourite of garden visitors, I must confess, but great shots of him Phil.

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  5. What an extraordinarily bonny beast. It'd be welcome on my lettuces any day. I must say I have never come across anything other than the all black arions in Northumberland. The regional variation in the most prevalent colour is a curiosity. I wonder why this happens, if it has ever been mapped and whether there is gradation or a sudden change. (Don't suppose you noticed if it produced interrupted slime trails or not!)

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  6. how bizarre! he seems like he stepped out of a lewis carrol story. i couldn't have made him up. and i love that bit about rocking side to side. beautiful photos!

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  7. A slug with character! The next to last shot is especially easy to assign anthropomorphic behavior to. Don't know how you managed to make it look so appealing and endearing. ;-)

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  8. Hi Lesley, my compost bin is the favourite hang-out for slugs too. I sort of hope that they'll stay there ... but maybe I'm too optimistic.

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  9. Excellent pictures and description, Phil. It's rather attractive, in a sluggish sort of way.

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  10. Hi Nigel, these little pocket digital cameras (this was a Pentax W20) are great down getting eye-to-eye pictures of low-life..

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  11. Hi Ellen, in this species I think the skin wrinkles like a concertina when it contracts..

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  12. Hi Keith, i know what you mean ... some people say the black slugs don't damage garden plants, but I've first-hand evidence that they do (and that they are also cannibals)...

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  13. Hi Nyctalus, some years ago we had a holiday in central France and all the Arion ater there were bright red - not a black one in sight. This individual was in the arboretum at the top of Hollingside lane and a population of red ones might have been intrdouced 40 years ago with some of the trees that were planted at that time. There were also black ones with a red frill around their foot. Didn't check-out its slime, but will next time!

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  14. Thanks Zoe, this was a slug with real character!

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  15. Hi Wilma, I just put the camera on the ground and let it crawl towards it ... and took a lot of pictures, half of which were out of focus. I've found that most of our wildlife looks more interesting if you get down to its level!

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  16. Hi Phil. I have a slugs/snails field guide translated from an eastern european original. Although billed as Slugs and Snails of Britain and Europe Arion ater gets only a passing reference in a piece about Arion rufus - the Red Slug. It says that some consider these two to be subspecies with the rufus form mainly in central and eastern europe and the black to the west. Apparently you tell them apart by features of their reproductive systems. So there's your next challenge! Could this be an immigrant Arion rufus brought in on arboretum trees from eastern europe?

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  17. Hi Nyctalus, certainly could have come in with imported plants. I used to run a class practical dissecting snails - their internal plumbing is amazingly complex and surprisingly variable amongst individuals. contrary to what the text books say they aren't all hermaphrodite - about 1 in 100 usually turned out to be male only.

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