Jeremy, the lonely left-handed snail, finally mates—and then dies

On September 21 I put up a post about a rare left-handed mutant of the garden snail, Cornu aspersa, named Jeremy.  (That post explains why snails of only identical coiling can mate, due to their hermaphroditism and the position in which they copulate.)  Nearly all garden snails (and 90% of all snail species) have right-handed coiling, but Jeremy, a one-in-a-million variant, is prized by snail collectors; he also could have started a new species of lefties that was reproductively isolated from right-handed snails. (This has in fact happened with other species in nature. It is the only form of single-generation speciation I know, and requires small and largely immobile populations—like snails.)

University of Nottingham inquiries led to the donation of two other lefties: “Lefty” and “Tomeu”. Sadly for Jeremy, they gave him (or rather it, since these snails are hermaphrodites) the cold shoulder, ignored him, and mated with each other.  Well, that’s good for producing a left-handed race, but not good for Jeremy’s libido.

However, all’s well that ends well, and, as NPR reports, Jeremy finally copulated with another lefty. And then he died.

Camila Dominoske, who wrote the piece, has found a sense of humor in this tragedy. Note the puns.

Jeremy, the rare snail with the left-curling shell whose search for a mate kicked off an international quest, has slithered off this mortal coil.

But there’s one last twist to the story. Reader, before he died, Jeremy procreated.

That’s right. The little lefty did it.

. . . Jeremy was found dead on Wednesday. But “the sad news comes with a bittersweet twist,” writes the University of Nottingham.

“Shortly before his death, Jeremy was finally able to produce offspring after mating three times with another ‘lefty’ snail, ensuring that his legacy will live on through continuing genetic studies into his rare mutation.”

(Three times! Nice work, Jeremy.)

Here is Jeremy and several left-handed pals (NPR’s caption): Jeremy is the small guy second from right:

Snails Senda (left), Jara, Tomeau, Jeremy and Indi hang out together at the University of Nottingham’s labs. Jeremy was the lab’s original sinistral snail; the others are his “Spanish pals,” as scientist Angus Davison puts it. Angus Davison/University of Nottingham

The striking thing about Jeremy’s offspring is that even though he mated with another lefty, their kids are all right handed! But this is understandable given the way snail coiling is inherited. I’ll try to explain it without screwing things up (correct me if I err and you know coiling genetics):

The coiling of a snail’s shell is not determined by its own genetic constitution, but by its mother’s!  While it’s not clear whether the eggs were produced by Jeremy or his left-handed mate, both were lefties. You can be a lefty even though you carry the dominant allele for “right-handed” coiling, so long as your mother was a lefty (l/l) but you inherited a right-handed allele from “dad” or are a mutant (you are L/l). All such offspring of the l/l  X L/l cross will be left-handed because their mother carried the genes for left-handedness, but you yourself could carry (but not express) the genes for right-handedness. I suspect Jeremy (and/or his mate, it’s not clear who produced the eggs) were both L/l snails but didn’t express the “right-handed” L” allele. However, their offspring would: if Jeremy was L/l and acted like the egg-producing “mother” (remember, they’re hermaphrodites), then his own genotype would determine the coiling of his offspring, and all of his own kids would be right-handed, since the product of L (right) is dominant over that of l (left) in the egg cytoplasm.  This is called maternal inheritance: an individual expresses its mother’s genetic constitution rather than its own, though it passes on its own genes to the next generation.

Here’s an analogy: suppose that we look at human eye color and assume that the brown allele (B) is dominant over blue (b), but that eye color is maternally inherited (it’s not; our eye colors reflect our own genetic constitution, not our mother’s; this is a hypothetical). Under maternal inheritance, if your mother was blue-eyed (bb) but mated with a homozygous (BB) brown-eyed male, all the offspring would still be blue-eyed because they’re showing their mother’s genotype, not their own. But every female offspring, being B/b, with brown being dominant, would produce all brown-eyed offspring, regardless of who they mated with.

This is very different from what you’d see if eye color were inherited normally, as it is. In that case the original cross would produce all brown-eyed offspring and the next generation could produce a mixture of brown or blue, depending on whom they mated with.  This form of inheritance, which differs from that seen by Mendel with his peas, was first worked out by a Drosophila geneticist: Alfred Sturtevant, who tested and confirmed his theory in further crosses using a different species of snail.

So what we have here is Jeremy and his mate having mothers homozygous for the left-coiling gene, but themselves carrying dominant right-handed alleles, perhaps because their own mothers had had a rare mating with a righty.

No worries, though, for the left-handed gene is still there in Jeremy’s offspring, even if they show right-handed coiling; further judicious further crosses can and will produce a batch of other lefties. Jeremy’s genetic legacy will live on!

That digression might have confused non-biologists (and I might even have screwed it up a bit), but what’s clear is that we know why two lefties can mate and produce all righties.

If you got through that, here’s a treat from the NPR site: Lydia Hiller’s rendition, in two parts, of “The Tragical Ballad of Jeremy the Left Twisting Snail”. She characterizes Jeremy’s coiling as a “birth defect,” but it’s not: it’s the expression of a rare allele.

RIP Jeremy. We don’t know whether snails get a form of pleasure from copulating, or if it’s just an imperative without a qualia reward, but I hope Jeremy had some fun before he shuffled off this mortal coil.



  1. Randy schenck
    Posted October 14, 2017 at 10:59 am | Permalink

    Very good and educational.

  2. Posted October 14, 2017 at 11:01 am | Permalink

    I’m a sort of musician and not a biologist at all, and all I fully understood from a hasty first reading was the double-entendre about screwing it up, but I can still tell it’s a very cool story! I can hardly imagine the consternation of scientists of earlier generations trying to untangle all that! [And then their delight in figuring it out.] Kind of like the codebreakers at Bletchley Park.

    • Posted October 14, 2017 at 11:16 am | Permalink

      Sturtevant was a genius: he just looked at a few generations of crossing data and the answer came to him instantly.

      • Mark Sturtevant
        Posted October 14, 2017 at 12:50 pm | Permalink

        I liked how you began that sentence, except for the was part. 😊

        • Posted October 14, 2017 at 4:04 pm | Permalink

          But. . . but. . .he’s dead!

        • gravelinspector-Aidan
          Posted October 14, 2017 at 9:07 pm | Permalink

          Any known relationship? It’s not one of the world’s most common family names.

        • Diane G.
          Posted October 15, 2017 at 4:03 am | Permalink


          FWIW, I did think of you when I ran across his name both in the article and Jerry’s comment.

  3. Posted October 14, 2017 at 11:08 am | Permalink

    I believe the snail was named after another well-known British “lefty”: Jeremy Corbyn.

  4. yazikus
    Posted October 14, 2017 at 11:18 am | Permalink

    I love this post. Good for Jeremy. I think I recall watching an episode of Isabella Rossellini’s Green Porno about snail mating. It was good.

  5. Posted October 14, 2017 at 11:41 am | Permalink

    Do snails have qualia? If you sprinkle them with salt they writhe as if in pain. So maybe Jeremy writhed in pleasure too.

    • gravelinspector-Aidan
      Posted October 14, 2017 at 9:12 pm | Permalink

      I shall just prepare the strapping-down board for you (vintage 1830, good and solid; and blood-soaked), then we can set about removing the waterproof part of your skin before establishing a baseline of qualia with a communicative and unanaesthetised specimen. I’ll just get the consent forms for you, but the short version is that this is going to hurt you a more than it’s going to hurt me.

  6. Posted October 14, 2017 at 11:43 am | Permalink

    As someone with situs inverses I lament the loss of a fellow chiral. I am, however, reminded by Jeremy’s plight that I should be grateful for having external bilateral symmetry; otherwise my own left/right mate choice would also have been anatomicaly, rather than just intellectually, constrained.

    • Diane G.
      Posted October 15, 2017 at 4:12 am | Permalink

      *googles situs inverses* Wow, you are one in 10,000!

      I’m impressed that your mate choice was intellectual. 😀

  7. Gregory Kusnick
    Posted October 14, 2017 at 12:06 pm | Permalink

    Thanks for the explanation of coiling genetics. What’s still missing is an account of how the maternal genome influences coiling in the developing embryo. Presumably it has to do with how eggs are produced, i.e. there are right-handed eggs and left-handed eggs, and the embryo adopts the handedness of the egg it’s in.

    I can think of two ways this could work. The egg itself could be coiled or twisted in some fashion, and the embryo is forced into a matching coil like being stamped out of a mold. Or there could be some biomolecule in the egg that induces left-handed coiling.

    In the latter case, if that molecule were introduced by, say, a fungal infection or an insect’s sting, we wouldn’t hesitate to call it a teratogen and the resultant non-standard coiling would be unambiguously a birth defect. I’m not sure why we should view it differently simply because the molecule was produced by a snail genome. Indeed there are many genetic diseases that are classified as birth defects.

    • Posted October 14, 2017 at 12:22 pm | Permalink

      This reference may help; it shows the developmental basis of coiling and how it starts in the egg, hence the maternal influence. I think they’ve identified at least one “coiling” gene now but I don’t have time to look it up.

      • Gregory Kusnick
        Posted October 14, 2017 at 2:17 pm | Permalink

        Yes, that did help; thanks. Executive summary: there’s a protein in the egg’s cytoplasm, inherited from the mother, that controls the orientation of asymmetric cell division (and hence coiling) in the embryo. In mothers with two recessive alleles, this protein is missing or defective, and the embryo coils to the left.

    • gravelinspector-Aidan
      Posted October 14, 2017 at 9:16 pm | Permalink

      In the latter case, if that molecule were introduced by, say, a fungal infection or an insect’s sting, we wouldn’t hesitate to call it a teratogen

      Isn’t there something similar involved in a number of amphibian population collapses, with an environmental (fungal?) teratogen producing developmental errors (“birth defects”) in amphibian embryos. Like, 4 hind legs.

  8. Jenny Haniver
    Posted October 14, 2017 at 12:20 pm | Permalink

    Here’s Jessye Norman with a fitting tribute: Liebestod

  9. Ken Kukec
    Posted October 14, 2017 at 1:51 pm | Permalink

    Attaboy, Jeremy!

    Always go out with a bang, is my motto.

    • Diane G.
      Posted October 15, 2017 at 4:14 am | Permalink


  10. ladyatheist
    Posted October 14, 2017 at 3:40 pm | Permalink

    What about mirror-image twins? Could Jeremy & his mate have been mirror twins with normal DNA?

  11. BJ
    Posted October 14, 2017 at 4:22 pm | Permalink

    He died the way many of us hope to: in the afterglow of a great orgasm 🙂

  12. Rick Bannister
    Posted October 14, 2017 at 4:25 pm | Permalink

    The story of poor Jeremy brought to mind one of the great animal songs by Flanders and Swann Misalliance.

    • Posted October 14, 2017 at 6:54 pm | Permalink


    • gravelinspector-Aidan
      Posted October 14, 2017 at 9:19 pm | Permalink

      I couldn’t find those cases last time I was at the NHM. Too busy nosing through the coelacanth collection, and being gob-smacked by the “wall of Ichthyosaurs” (not that they’re all ichthyosaurs).

  13. Diana MacPherson
    Posted October 14, 2017 at 6:23 pm | Permalink

    What a slap on the shell that the other lefties ignored Jeremy & mated with each other. Poor Jeremy.

    • Posted October 14, 2017 at 6:54 pm | Permalink

      Yeah, but he did get the last…uh…laugh?

  14. BJ
    Posted October 14, 2017 at 9:55 pm | Permalink

    Jerry, you’re correct that it shouldn’t be called a “birth defect.” The politically correct way to say it is “spiralatypical.”

  15. Posted October 15, 2017 at 2:29 am | Permalink

    Hmm, another entomologist named Sturtevant. Coincidence?

  16. Arno Matthias
    Posted October 15, 2017 at 10:40 am | Permalink

    funny take by the “No such thing as a fish”-team:

  17. Liz
    Posted October 15, 2017 at 12:43 pm | Permalink

    I’m wondering why we don’t know whether or not snails have pleasure when copulating.

  18. Posted October 16, 2017 at 6:19 am | Permalink

    As geneticist (and Jeremy’s scientist) I have colleagues that struggle to understand the maternal inheritance of shell coiling.

    A good analogy is the colour of a bird’s egg – as in snail shell coiling, the colour of an eggs is due to maternal genes. The difference is that there is a direct and obvious link between the bird mother and the egg shell colour, whereas the link between snail mother and egg coiling direction is less clear – something that we are investigating in the lab.

    • Posted October 16, 2017 at 6:30 am | Permalink

      Is Jeremy’s shell going to be preserved as a memorial?

      • Posted October 16, 2017 at 11:27 am | Permalink

        The shell is on my desk at the moment, with the body in the -80 freezer. Any suggestions?

        • Posted October 16, 2017 at 11:35 am | Permalink

          Bronze it, and have a tiny little etched plaque- you can get a tasteful one made at a Petsmart vending machine inexpensively, then glue both to a nice piece of finished hardwood.

          Better yet, put out a public call to artists/creatives/left-handed folk, to come up with a suitable memorial. Maybe more than one. Don’t let the legacy die!

  19. Posted October 17, 2017 at 11:51 am | Permalink

    Astonishing – and so wonderful – that we *understand* these things!

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