A Millipede Mystery

For such a small island, Tuckernuck has a disproportionately large number of mysteries. From the ghostly tales and warnings of the Yoho to the altogether unique song-type of the Black-capped Chickadees (Poecile atricapillus) found on Tuckernuck Island, there are countless stories and observations to get one searching for answers. My friend Skyler and I were on Tuckernuck researching the latter of the two aforementioned mysteries but stumbled across the answer, or perhaps part of the answer, to an entirely different mystery.

First of all some background is required. Part of this millipede mystery is why there are Giant Millipedes (Complex Narceus americanus) on Tuckernuck at all. The soil on the island is very sandy if you can even call most of it soil at all. The vegetation is very short due to the exposed nature of Tuckernuck, and the forest floor is mostly dry with leaf litter only where trees are most dense. This is noticeably different to the Giant Millipede's usual habitat of more humid old growth forest with extensive decomposing matter on the ground. The habitat on Tuckernuck just shouldn't support these millipedes from what is currently known about them, and it shows; Complex Narceus americanus has never been recorded on Cape Cod, Martha's Vineyard, or even Nantucket Island. They are completely isolated on Tuckernuck Island (Update: A population has been discovered on Coatue, Nantucket on June 17th, 2022). However, this isn't even the strangest part. Every spring and summer, countless millipedes are found headless along the trails and beaches of Tuckernuck Island. Some are further broken apart but the freshest ones are found only with their heads missing. This phenomenon occurring with Complex Narceus americanus has only been documented from a few places (including upstate New York) and has been a popular ecological mystery of Tuckernuck since at least the 1940s (Mckenna-Foster, Beaton, & Millman). American Giant Millipedes can release a harmful fluid that can cause burns (Wikipedia, 2022), so presumably the head is the only safe piece of the animal to consume. Clearly something on Tuckernuck has figured this out. A team funded by the Nantucket Biodiversity Initiative went to Tuckernuck in 2009 in an attempt to solve this mystery. They collected some very important data and information, but were not successful in finding the culprit to these decapitations. And that's how it stayed. A complete mystery. While many islanders and researchers had their theories about what was causing this phenomenon, no one was sure. Small mammals or birds were the main suggestions, and until June 7th, 2022, suggestions were all they were.

Skyler and I had planned to have 4 mornings of recording Black-capped Chickadee song on Tuckernuck Island, but days 3 and 4 were to be interrupted by winds, rain, and thunder sent North by a storm from the Bahamas. While it wouldn't technically be a tropical storm by the time the weather reached us, it was looking more and more like we wouldn't be able to record at all on our final 2 days. In the evening of day 2, we decided to try and get back onto Nantucket Island before the storm hit. We wanted to make sure we could get off Tuckernuck in time, and we wouldn't have been able to obtain any more recordings the next couple of days. Skyler attempted to call our ride off of Tuckernuck but to no avail, so he quickly began making his way to North Head to return a pot that needed to be returned before we left. Meanwhile our ride off island, Mark, tried calling Skyler. This was unsuccessful due to the poor signal on parts of the island, so Mark drove to the field station where we were staying. Eventually Skyler made his way back and I had packed up most of our stuff in order to leave as soon as possible, but there was still some of Skyler's belongings that he needed to pack before we hopped in Mark's truck and headed to the boat. Skyler climbed up to the loft and began packing up. After a couple minutes he looked out the small loft window and saw it; something was thrashing a millipede around beneath the bird feeders. That something was a Common Grackle (Quiscalus quiscula). He immediately yelled "Lily! Look out back a grackle is attacking a millipede!" While barely processing what he said, I ran to grab my camera and exited the field station in a rush of adrenaline. The door slammed behind me and all the birds flew off of the feeders, particularly a Common Grackle flew off of the ground and into a nearby shrub. I quickly tried snapping some photos but it flew slightly further back onto a higher branch. This is where I was finally able to obtain photographs. I watched as the grackle cleaned its bill by rubbing it against the branch, and a few drops of some type of liquid dripped off the end of its bill. Skyler followed me outside shortly after and we ran over to investigate the area on the ground where the grackle had been. We made our way over to the bird feeders and there it was, a sight Tuckernuckers are all too familiar with. Right on the ground beneath the feeders exactly where the grackle had been; one giant millipede but missing a very important feature: its head. The body was still wriggling slowly as Skyler picked it up, and the legs were moving as they often do for a while after the decapitations occur. With literally minutes to spare on Tuckernuck, we'd solved it, or so we thought. We loaded up the final bags and hopped in the back of Mark's pickup truck as he drove off towards his boat.

On our way back we began thinking. How could Common Grackles be the only culprit to these decapitations? Tuckernuck is a small island and the fauna is very different from the mainland. Common Grackles are present but not extremely abundant on island. Excepting large flyover migrant flocks, there typically isn't more than a few dozen grackles on Tuckernuck at a time. Would these be enough to account for the hundreds of headless millipedes that are scattered throughout the island every year? Since neither of us observed the grackle actively consuming a portion of the millipede, what if it was already decapitated and the grackle just tossed it around and then cleaned its bill after eating some nearby bird seed? While this explanation seems unlikely it can't be completely discounted as we didn't directly observe it consuming the head of the millipede. Why is this phenomenon limited to a few specific locations involving this millipede complex? Is the benefit that great for grackles to be eating just a tiny portion of each animal? It also still remains to be seen why the millipedes are so hyper-abundant on Tuckernuck in the first place. Could these millipedes represent a unique species? Perhaps DNA testing could help to understand this aspect. And if it's not just grackles, what other species are decapitating the millipedes of Tuckernuck Island? Our findings add a large piece to this puzzle, but don't completely solve all aspects of the millipede mystery of Tuckernuck Island. Maybe Tuckernuck will hold on to this mystery for as long as it can, as it tends to do. Maybe we'll never know the full picture. But the allure is in the questions and mysteries, and that's part of what makes this island so special.

Until next time, Tuckernuck.

Citations:
Mckenna-Foster, A., Beaton, C., Millman, L. (2009). An Investigation into headless millipedes on Tuckernuck Island, MA. DOI

Wikipedia. 2022. “Narceus americanus.” Last modified December 8, 2021. https://en.wikipedia.org/wiki/Narceus_americanus.

הועלה ב-יוני 8, 2022 02:06 אחה"צ על ידי liliumtbn liliumtbn

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liliumtbn

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יוני 7, 2022 05:22 אחה"צ EDT

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The one that got us closer to solving the mystery: https://www.inaturalist.org/journal/liliumtbn/66969-a-millipede-mystery

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liliumtbn

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יוני 7, 2022 05:07 אחה"צ EDT

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Very interesting! I'm not surprised to learn grackles are the culprit; some individuals have been known to develop unusual foraging habits along such lines. Individuals who will specialize in killing young birds, exhausted migrant warblers, or mice flushed by farm equipment, and then extracting and eating their brains have been documented. I did a bit of research on this back in undergrad after witnessing a grackle do this to a fledgling house sparrow in my yard. They are very clever foragers, and if they find a new niche, may exploit it relentlessly.

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Wow @jlayman that's super interesting! I knew they were opportunistic but I didn't realize quite the extents that they go to exploit new food sources.

פורסם על-ידי liliumtbn לפני יותר משנה

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