Oh man, once again you have me out crawling around on glacial till, scraping my knees, looking for stuff. You sounded real good today on Rumble Strip- made us proud.
Hello fellow Vermonter! I found one of these flatworms last week in Swanton and just uploaded to iNaturalist. I have a lot of amber snails in my backyard and the birds are plentiful so it must be fate! Great article, too, btw!
Hey, this is a different species than what I report on! (Which is why I didn't see it.) This one is not as commonly reported in the US, even though it's native to North America. AWESOME find!
I’m up near Burlington and one of these snails made its way up to a second story window on my house. I got closer and saw the creepy pulsating eye stalks…and the good old internet brought me here to learn more. Thanks for the information
Great! Not really a way to share it here. If you're an iNaturalist user, I encourage you to post it there. Otherwise, send it to me (bryan@bryanpfeiffer.com) and I can post it for you. All I'd need is a date and location (and I won't provide the exact location unless that's okay with you). Thanks!
We found one in a perennial pot at Red Wagon Plants in Hinesburg on Thursday! Two broodsacs, very active for hours until they retreated under the shell (they would still occasionally pulse). Must be the season for them. Happy to send video if you’d like to add to your collection. Did you find out what the average lifespan of a host snail is and/or whether they continue to eat as normal?
Hey Sophie. Sorry I failed to keep up with comments last year. Glad to hear of your encounter! (I'm back to these snails this year.) Any chance you can post your observation to iNaturalist? Or perhaps you already did? (I have no clue on the lifespan, but I'll look into it.)
Your trematode is a digeneid, meaning it has two hosts. Trigeneids also exist. You didn't mention which birds eat it, but I'm guessing multiple species. Digeneid Parasites that have a specific intermediate host can't be too picky about their final host or vice versa. Otherwise they might not get passed on. Something similar happens in certain crab species, but only about 5% show external egg sacs, like your snails. Higher rates might harm the host population. And we do call them Zombie crabs.
Hey Brad. I'm so sorry I failed to keep up with comments on this last year. I'm really glad you chimed in. (I'm back at it with the snails now in 2025.) I'm not sure we have much evidence at all on which birds eat these occupied snails. But, yeah, probably many. The literature is scarce to non-existent on it. If a bird plucks a broodsac from a snail, you wouldn't happen to know whether the Succineidae can regenerate their eye stems, would you? I've read that it's the case, but I'm skeptical.
It's interesting to watch the amalgam of visceral emotions this article elicits in me. The pulsating broodsac is, well, pretty, in an AI kind of way. To imagine something burrowing into eyestalks, horrible. There's also curiosity about how it works. I admire you for your thoroughness and tenacity. (I'm still working on rehabilitating my early-trained attitude toward insects. Snails are easier. Broodsacs in eyestalks? That I don't know about. Will have to revisit, when I feel stronger.)
I do hope you're feeling stronger this year, Diane. (Sorry I lost track of the comments threat last year.) I'm back to the snails for the 2025 field season!
Bryan, what an intriguing post. I have seen/heard of these parasites previously, and found them to be both horrifying (the thought of parasitism is horrifying to us at the core, I think) and fascinating. You stated: "We could even speculate that it’s the snails running the show here, climbing higher and exposing themselves so that birds will come along and pluck those broodsacs from their eyestalks, which the snails reportedly can then regenerate." Are there, indeed, instances of the birds removing the broodsacs from their eyestalks, and the snails actually regenerating the previously parasitized tissue/body parts?
Hi Jewel. Well, I'm terribly sorry that I failed to keep up with comments on this post. I'm back to it with updates this summer because occupied snails persist at my "study site." I'll be watching them again and updating this post.
As to your question about birds remoing the broodsacs and the snails regenerating their body parts, I'll confess that I don't know for sure. I read it at least one of the papers cited below. But it's no doubt worthy of further investigation. I'll see what else I can find.
Again, my apologies for straying from comments last year (sometimes it's hard to keep up with all of them.).
This was so fascinating! Not something I ever would have thought to investigate, but I'm so glad I know a writer who does.
And something I thought of regarding the clickbait. When you've built enough trust with your readers, you don't need clickbait titles. We're going to read your essay because we know we'll like it.
Ha! Great point! 😀 In one sense, however, you need not subscribe in order to complete your own life cycle. (But, oh, if only Substack were indeed an essential intermediate host for readers -- or music creators, for that matter.)
Wonderful piece, Bryan. Thanks for taking the barb off the clickbait hook and talking about parasites with such cool, calm appreciation. I learned for a piece I wrote a while back that parasitism is far more common than most of us realize (certainly more than I realized), with over half of animal species (mostly helminths, protozoa, and arthropods, I think) and more than 4500 plant species harvesting their energy from other species. It really changes the way I see the world, but that means I also have to rethink parasitism too. It's hard to get past the horror movie imagery - no shortage of examples - but as you say here we don't really know what it means to the little things who run the world.
I haven't looked that hard yet, but it would be useful for a possible reboot of my microbial Anthropocene piece. It seems like something she would say.
That's brilliant (as was everything about her). Reminds me of my half-joking idea that - akin to the apparent behavior modification of toxoplasma gondii - that there's a microbe on Earth that wants to spread to other planets, and it's driving the weird modern human desire to explore space. Musk always looks to me like he has an acute infection...
Yeah, but maybe somehow we can make it into a story of shared history and the routines and tribulations of life going on for hundreds of millions of years? 🤔 🐌🐦⬛🐛🪱
Fascinating and so full of your curiosity. I have been battling an invasions of small ant battalions for several weeks and you have inspired me to learn more about why they are here and what is the purpose of making home in my kitchen. Much less frustrating and perhaps we will make peace. Thank you.
Ants in the kitchen -- often a tough one. I applaud your openness to learning about their lives in cupboards! I wish I could suggest some reading on that -- but I suspect you'll find some. Thanks, Leslie.
Isn’t part of exuberance, curiosity, and an open mind placing oneself in the snail’s shoes… or 🐚… to empathize with what they might be experiencing? I agree that click baiting stories about creatures is selfish. I wonder if viewing snails and worms from a detached point of view can blind the viewer from intuitive awareness and compassion for all involved in these delicate sentient cycles of life and reciprocity. Thanks for the article!
This is a fine perspective, Susan, with many angles. One of them is that snails, birds, and trematode flatworms basically co-evolved. They've been in the survival business together for hundreds of millions of years. It's sort of "routine" for them. How we ourselves might sympathize or empathize with that shared evolution is, in the end, I guess, a personal decision. As for me, my awareness and compassion tend to be more so for organisms that suffer owing to adverse human impacts on their habitats and lives. We've got control over those impacts — or so I'd like to believe. Thanks again!
Oh man, once again you have me out crawling around on glacial till, scraping my knees, looking for stuff. You sounded real good today on Rumble Strip- made us proud.
Hello fellow Vermonter! I found one of these flatworms last week in Swanton and just uploaded to iNaturalist. I have a lot of amber snails in my backyard and the birds are plentiful so it must be fate! Great article, too, btw!
Awesome. Thanks! (Hmmm. I'm looking for your iNat record. Can't see it.)
Still learning how to use iNat, but here is my url: https://www.inaturalist.org/observations/304230347
Hey, this is a different species than what I report on! (Which is why I didn't see it.) This one is not as commonly reported in the US, even though it's native to North America. AWESOME find!
Right?! Nature is cool 😎
I’m up near Burlington and one of these snails made its way up to a second story window on my house. I got closer and saw the creepy pulsating eye stalks…and the good old internet brought me here to learn more. Thanks for the information
Great news, Adrienne! Thanks for the report. Any chance you got a photo?
Yes! I got a photo and a video! Is there a way to share here or…?
Great! Not really a way to share it here. If you're an iNaturalist user, I encourage you to post it there. Otherwise, send it to me (bryan@bryanpfeiffer.com) and I can post it for you. All I'd need is a date and location (and I won't provide the exact location unless that's okay with you). Thanks!
Sent you an email!
We found one in a perennial pot at Red Wagon Plants in Hinesburg on Thursday! Two broodsacs, very active for hours until they retreated under the shell (they would still occasionally pulse). Must be the season for them. Happy to send video if you’d like to add to your collection. Did you find out what the average lifespan of a host snail is and/or whether they continue to eat as normal?
Hey Sophie. Sorry I failed to keep up with comments last year. Glad to hear of your encounter! (I'm back to these snails this year.) Any chance you can post your observation to iNaturalist? Or perhaps you already did? (I have no clue on the lifespan, but I'll look into it.)
Your trematode is a digeneid, meaning it has two hosts. Trigeneids also exist. You didn't mention which birds eat it, but I'm guessing multiple species. Digeneid Parasites that have a specific intermediate host can't be too picky about their final host or vice versa. Otherwise they might not get passed on. Something similar happens in certain crab species, but only about 5% show external egg sacs, like your snails. Higher rates might harm the host population. And we do call them Zombie crabs.
Hey Brad. I'm so sorry I failed to keep up with comments on this last year. I'm really glad you chimed in. (I'm back at it with the snails now in 2025.) I'm not sure we have much evidence at all on which birds eat these occupied snails. But, yeah, probably many. The literature is scarce to non-existent on it. If a bird plucks a broodsac from a snail, you wouldn't happen to know whether the Succineidae can regenerate their eye stems, would you? I've read that it's the case, but I'm skeptical.
It's interesting to watch the amalgam of visceral emotions this article elicits in me. The pulsating broodsac is, well, pretty, in an AI kind of way. To imagine something burrowing into eyestalks, horrible. There's also curiosity about how it works. I admire you for your thoroughness and tenacity. (I'm still working on rehabilitating my early-trained attitude toward insects. Snails are easier. Broodsacs in eyestalks? That I don't know about. Will have to revisit, when I feel stronger.)
I do hope you're feeling stronger this year, Diane. (Sorry I lost track of the comments threat last year.) I'm back to the snails for the 2025 field season!
Bryan, what an intriguing post. I have seen/heard of these parasites previously, and found them to be both horrifying (the thought of parasitism is horrifying to us at the core, I think) and fascinating. You stated: "We could even speculate that it’s the snails running the show here, climbing higher and exposing themselves so that birds will come along and pluck those broodsacs from their eyestalks, which the snails reportedly can then regenerate." Are there, indeed, instances of the birds removing the broodsacs from their eyestalks, and the snails actually regenerating the previously parasitized tissue/body parts?
I am entertained, as always - Jewel Adams, PhD
Hi Jewel. Well, I'm terribly sorry that I failed to keep up with comments on this post. I'm back to it with updates this summer because occupied snails persist at my "study site." I'll be watching them again and updating this post.
As to your question about birds remoing the broodsacs and the snails regenerating their body parts, I'll confess that I don't know for sure. I read it at least one of the papers cited below. But it's no doubt worthy of further investigation. I'll see what else I can find.
Again, my apologies for straying from comments last year (sometimes it's hard to keep up with all of them.).
This was so fascinating! Not something I ever would have thought to investigate, but I'm so glad I know a writer who does.
And something I thought of regarding the clickbait. When you've built enough trust with your readers, you don't need clickbait titles. We're going to read your essay because we know we'll like it.
I'm back watching them this year -- they do persist from year to year (at least at my "study site").
Awesome, even if their appropriated eyes make me squirm.
Thanks, Amy. Yeah, I know it's tough for some folks. It's the world -- it's nature.
Glad to know that fascinating and squeamish can be somewhat compatible! :-)
If I subscribe, does that make you my host?
Ha! Great point! 😀 In one sense, however, you need not subscribe in order to complete your own life cycle. (But, oh, if only Substack were indeed an essential intermediate host for readers -- or music creators, for that matter.)
Wonderful piece, Bryan. Thanks for taking the barb off the clickbait hook and talking about parasites with such cool, calm appreciation. I learned for a piece I wrote a while back that parasitism is far more common than most of us realize (certainly more than I realized), with over half of animal species (mostly helminths, protozoa, and arthropods, I think) and more than 4500 plant species harvesting their energy from other species. It really changes the way I see the world, but that means I also have to rethink parasitism too. It's hard to get past the horror movie imagery - no shortage of examples - but as you say here we don't really know what it means to the little things who run the world.
Thanks, Jason. Then there's that great quote attributed to Lynn Margulis, something like:
"Birds are how microorganisms fly, fish are how microorganisms swim, and humans are how microorganisms think."
Bryan, do you know where I can find that Margulis quote? A quick search didn't turn it up. No problem if not.
Crap -- I don't have a good reference for it. If you can't find it, I probably can't. Yikes!
I haven't looked that hard yet, but it would be useful for a possible reboot of my microbial Anthropocene piece. It seems like something she would say.
That's brilliant (as was everything about her). Reminds me of my half-joking idea that - akin to the apparent behavior modification of toxoplasma gondii - that there's a microbe on Earth that wants to spread to other planets, and it's driving the weird modern human desire to explore space. Musk always looks to me like he has an acute infection...
This would make a great horror film!
Yeah, but maybe somehow we can make it into a story of shared history and the routines and tribulations of life going on for hundreds of millions of years? 🤔 🐌🐦⬛🐛🪱
Fascinating and so full of your curiosity. I have been battling an invasions of small ant battalions for several weeks and you have inspired me to learn more about why they are here and what is the purpose of making home in my kitchen. Much less frustrating and perhaps we will make peace. Thank you.
Ants in the kitchen -- often a tough one. I applaud your openness to learning about their lives in cupboards! I wish I could suggest some reading on that -- but I suspect you'll find some. Thanks, Leslie.
Isn’t part of exuberance, curiosity, and an open mind placing oneself in the snail’s shoes… or 🐚… to empathize with what they might be experiencing? I agree that click baiting stories about creatures is selfish. I wonder if viewing snails and worms from a detached point of view can blind the viewer from intuitive awareness and compassion for all involved in these delicate sentient cycles of life and reciprocity. Thanks for the article!
This is a fine perspective, Susan, with many angles. One of them is that snails, birds, and trematode flatworms basically co-evolved. They've been in the survival business together for hundreds of millions of years. It's sort of "routine" for them. How we ourselves might sympathize or empathize with that shared evolution is, in the end, I guess, a personal decision. As for me, my awareness and compassion tend to be more so for organisms that suffer owing to adverse human impacts on their habitats and lives. We've got control over those impacts — or so I'd like to believe. Thanks again!
That was well worth every minute of reading. Thank you for taking the time to wonder and then to share your research and insights with all of us.
So great. I'm looking forward to next year's video of a bird munching on a broodsac in the wild.
I'll be famous! 😝