Fun with slugs

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This is not a title I’d every imagined myself writing. Slugs in the garden are brown and squidgy, and we respond with a shudder and an “Errr, yuck!”.

But sea slugs are a different group of beasties altogether. As you can see from the pictures on this page, they’re not the boring brown critters we find eating the lettuce. And one species has a surprise that I’ll save for the end of this post.

The sea slug above, Flabellina iodinea or Spanish shawl, is brilliantly coloured partly as camouflage (yes, camouflage – the bright orange blends in with the colour of food that they sit on while eating) and partly to warn off predators – those pretty red appendages, used to extract oxygen from sea water, are also used to store stinging cells from the anemones they eat.

Glaucus atlanticus. Image from Wikimedia Commons.
Glaucus atlanticus. Image from Wikimedia Commons.

Then there’s Glaucus atlanticus. This is another stunning, although small, sea slug, and it too stores stinging cells from its food, which includes  the Portugese man o’ war. It, too, looks quite distinctive, again to warn potential predators that it’s likely to be more trouble than it’s worth.

I do find myself wondering about a couple of things. Firstly, how they manage to ingest the stinging cells without triggering them, and are then able to store and use these cells. And secondly, did the ability to do this evolve concurrently with the distinctive appearance, or did one precede the other?  If slugs that store stinging cells looked just like any others, there would be no evolutionary advantage to them, because predators wouldn’t be able to tell the difference, and if they had the appearance but not the stinging ability, predators wouldn’t be dissuaded from eating them.

You can find a great deal more information about these fascinating slugs (and others) from this post on Ecologica. Look for the Elysiella pusilla, a slug that can take chloroplast cells from the algae that it feeds on and incorporate them into its own body, which not only turns it green but also allows it to photosynthesise. In this case it is easy being green.

But the big surprise is a species called Chromodoris reticulata. This species, like many nudibranchs, is simultaneously hermaphroditic: that means that the creatures mate in pairs using both male and female parts at the same time.

Chromodoris reticulata goes further than other nudibranchs, however, by detaching its penis after mating. Now it’s not the only species that does this: orb-weaving spiders, periwinkles, and some land slugs also lose their male part after mating. The big surprise with this one is that it can grow another.

Japanese scientists from the Osaka City University and Tokyo’s Nihon University discovered that this species has a coiled spiral inside the body that rapidly uncoils after mating and grows into a new penis. Think of it like a propelling pencil or a Stanley knife (I believe American readers call these ‘boxcutters’): a few hours to add some finishing touches and it’s ready to go again.

I don’t know about you, but I can’t help being reminded of this song (warning: NSFW).

[Featured image: Spanish shawl (Flabellina iodinea). Image by Jerry Kirkhart, licenced under Creative Commons 2.0.]


    1. They’re amazing, aren’t they? 8 inches long and bright pink – it’s a wonder that they’ve survived…

      1. Now there’s a thought – a bit of whipped cream and a dash of cinnamon and they’d be just the ticket (imagine me gagging behind my hand here).

      2. Besides, there are some who advocate eating bugs and slugs to solve the crisis of food shortage, food source depletion, environmental destruction and land degradation.

      3. Indeed: given the reduction in the numbers of vertebrate and invertebrates from the likes of overfishing and so on, it’s been said that we’re going to end up eating jellyfish along with the bugs and slugs. Going down the food chain because we’re destroying it progressively, in other words, which is heartily depressing.

      4. We are doomed if we cannot learn to behave sustainably as individuals and as a species. Given that the environmental, social, political and economic issues and problems seem to be getting larger (and in many cases more dire) by the year, I seriously wonder whether space travel is even affordable and/or sustainable in the future, even when there are many who reckon and advocate that going into space is the (only) solution.

        The trick or problem is whether we could leave the Earth before we wreck it, and before serious disasters cause the decimation or even extinction of the human species. It is not just a question of whether the issue or vision is being seen as utopian or dystopian.

        Besides, since the human species has not (always, adequately and/or consistently) been a good custodian of the environment and the Earth (not to mention countless wars, atrocities, resource depletions, species extinctions environmental degradations and so on, plus an area of rainforest as big as 100,000 football courts is being cleared or destroyed everyday), there is no guarantee that once the human species migrates to another planet, the same trick or problem would not again surface and plague us, perhaps at an even quickening and/or devastating pace as a result of better and greater expansion, production and technology. We would export our baggage and problems to other worlds!

        A friend of mine wrote to me:

        I think if we went to Mars, we’d deal to it the same way we’re currently dealing to Earth. Richard Attenborough summed it up when he referred to us as the ‘scourge’ of the planet. Caused an outcry, but it seems to be true. Jared Diamond has published a good analysis of it, if a little deterministic for my liking. The reason would seem to be a faulty survival mechanism – hard-wired techniques for maximising resources that worked when we were on the ragged edge of extinction in the ice age, but now serve to create problems.

        Perhaps we could also liken humans as cancer cells on the petri dish that is Earth.

        By the way, I really look forward to your reading and commenting on the analyses and discussions at

        Thank you.

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