Not-quite-a-thousand feet

Millipede, Narceus annularis

We’ve had some “trouble” with critters invading the house here; I put trouble in quotations because although they are more than just the odd bug here or there, they’re generally (except the mosquitoes) not going to eat much, and so I cheerfully tolerate them. They’ve mostly been invertebrates of one sort or another, although we have had a chipmunk come to visit a few times as I’ve left the front door standing open for extra light and air circulation and he’s snuck in while my back was turned (I’m sitting typing away at my computer and hear something playing with the knobs on the ends of the drawstrings for the blinds). When the front porch light is on in the evenings it can draw quite a collection of insects, not just moths, and opening the door to go in and out often draws them in with you.

The ones that I haven’t figured out where they come from, though, are the millipedes. I suppose they, like the chipmunk, could also make their way in through the open door while my back is turned, though they always turn up at weird times of the day, and in weird spots. I’ll be going to refill my drink from the kitchen, and there’ll be one trundling across the middle of the kitchen floor. Or in the entry hall (that we rarely use) or in various corners. They all seem to stay downstairs, though, I have yet to see one upstairs. The one in the photo above was properly outside, on the deck. Millipedes curl up like this, with their head tucked safely in the centre, for protection against the threat of predators. It’s a characteristic of the group, and yet, virtually all of these guys that I’ve picked up have refused to curl up, instead waving their head about to show their displeasure.

Millipede, Narceus annularis

I probably wouldn’t have noticed them at all or paid them much attention if it weren’t for their size. These millipedes are enormous. They’re members of the species Narceus annularis (closely related to and hard to tell apart from N. americanus, but Bev of Burning Silo, also a resident of eastern Ontario, indicates the former species is the one found here), which I’ve seen referred to on some websites as the American Giant Millipede. They’re not kidding with that label. The one in the photo above, while a larger individual, is not by any means the largest I’ve encountered here; the biggest ones can be as long as from the tip of my middle finger to the deep crease that crosses the middle of the palm of my moderately-sized woman’s hands. You would expect to find invertebrates of this size under the rocks of the tropical forests or in the tombs of the sort that Harrison Ford frequents from time to time, but it seems out of place in the middle of the temperate forests of eastern North America.

Millipede, Narceus annularis

In fact, this species is wide-ranging and relatively abundant. It’s found through much of the east, from Florida north into Ontario, and west as far as Texas. They generally inhabit moist deciduous forest floors, munching on decomposing leaf litter and other detritus, though Bev also suggests, based on her own observations, that they may also forage on wet mosses or dead animals. In any case, their mouthparts are designed for chewing on soft materials, and they are therefore incapable of biting.

It’s funny, but despite the wide range, it’s another one of those species, like the Common Loon, that I tend to think of as “northern”. My parents’ place, while a patchwork of trees and swamp and scrubby area itself, contains a little deciduous forest, and is surrounded by quite a bit more, including huge swaths that make up portions of the Bruce Trail (which incidentally happens to pass right by their front door – handy for enterprising young children who want to make a few bucks selling fresh apples to hikers). I can see no reason, based on the habitat descriptions I’ve read, why these millipedes wouldn’t be found at my parents’ place also, but they’re not. The only places I’ve encountered them have been at a friend’s cottage, and now here, both at more northern latitudes.

Millipede, Narceus annularis

They’re nocturnal foragers, and although I do encounter some during the day as they cross open spaces from one pile of leaves to another, I’ve seen the most, and certainly the largest, at night. As part of mothing activities I’ve spread a sweet mixture onto the trunks of a few trees to try to draw in nectar-feeding moths. So far all I’ve really succeeded in drawing in were a few earwigs – and dozens of millipedes. Even though it doesn’t seem much like their usual fare of decomposing organic materials, perhaps the smell of something fermenting (beer and a mushed-up banana are part of the mixture’s recipe) appeals to them.

Millipedes mating, Narceus annularis

They’re around all year, spending the winter buried under logs and bark, and coming out in the spring once it warms up. For most of the warm months they generally stick to the leaf litter, perhaps now and then crossing a trail or otherwise exposing themselves as they move from one place to another. However, they become increasingly easy to see during the months of August and September – that is, now, which is perhaps why I’ve seen so many since moving here. And this is why: these are the months where they start to get amorous and look toward increasing the population. As I went about checking the moth mixture for any actual moths, I discovered these two, tightly entwined in love’s embrace – or whatever passes for love to a millipede. I snapped a few shots but didn’t stop to ask.

Both male and female have internal structures called gonopores on their 3rd body segment (the first being the head) where the eggs and sperm are created.The legs on 7th segment of the male (the larger of the two here; you can see the gap in his legs created by the shortened 6th set of legs, on his 7th segment, actually clearer on the original photo) are modified into mating appendages called gonopods (gono, of course from the same root as gonads, and pods, meaning feet) that the male uses to guide the spermatophore to the appropriate location. To transfer the spermatophore to his 6th set of legs the male curls his head down to his body so he can reach. The female has normal legs on her 7th segment, since she’s not guiding sperm anywhere, at least not externally.

Females make an underground nest that they line with what’s effectively millipede poop, using the folds on their “tail” segment to smooth it into shape. They lay their eggs in this chamber, usually a few hundred. The eggs hatch and, depending on the species, the larvae may remain in the nest for up to the first three instars (growth stages as separated by skin-sheddings).

Millipede, Narceus annularis

This one seems to be a female, having just normal legs on its seventh segment.

Check out all those little legs. Every one of the millipede’s body segments have two pairs of legs, with the exception of the head and “tail” segments, and the first four behind the head, which have just a single pair of legs each. Despite their name, millipedes never have a thousand legs; even the species with the most numerous appendages top out at “just” 750. On average for this species is maybe somewhere around a couple hundred.

Millipede, Narceus annularis

I counted up the segments on this individual that I found; it has 49 segments with two pairs of legs each, and four segments with one pair of legs each, for a total of 102 pairs of legs, or 204 legs total. And I have trouble just coordinating my two sometimes! They move their legs in the same way an earthworm moves its body, with undulating waves of footsteps that you can sort of get an inkling of from the photo of the one on my palm.

Millipede, Narceus annularis

They have eyes that resemble the compound eyes of flies and other insects, but are really just simply flat-plated occelli arranged into a group. Different species have different numbers of occelli; I did a quick count and this one seems to have about 35. The eyes aren’t good for much more than sensing light and dark, and perhaps basic shadows, they can’t detect shape or detail like an insect’s compound eye. Millipedes also have short little antennae that they use for sensing their immediate surroundings, and, in some species, possibly detecting the pheromones of the opposite sex, as well.

You can’t really see it well in any of the photos I have here, although if you look closely at the ones mating you can sort of detect it, but along their sides millipedes have small little breathing holes called spiracles. They use these as nostrils of sorts, but some species will also exude a noxious substance containing hydrogen cyanide, which can burn and discolour the skin, an effective defense against most predators. Supposedly (I found out after the fact) Narceus sp. are among this group of species, but of all the ones I’ve handled, not one has secreted anything, noxious or not.

Millipede, Narceus annularis

Like all hard invertebrates, millipedes wear their skeleton on the outside – it has the appropriate name of exoskeleton. This is the main reason insects shed their skins as they grow, they don’t have the means for the skeleton to grow along with the body, so when things start getting tight inside, they ditch the old skeleton and form a new one. Millipedes add a few extra segments (and therefore extra legs) with each successive moult. I found this shed exoskeleton (or possibly the empty skeleton of a dead individual) when I rolled over a log in my hunt for millipedes to photograph.

Millipedes are an ancient group of organisms, with the oldest fossils dating back some 420 million years, almost twice as long ago as the earliest dinosaurs. There are an estimated 80,000 species of millipede in the world today, of which only 10,000 or so have been described by science. Of these, about 1,400 are found in North America north of Mexico. There are 14 species of Narceus, all found east of the Rocky Mountains, and most in the southeastern part of the continent. Up here in Ontario we seem to have just the one, N. annularis, with N. americanus found in other parts of the northeast. Still, with something this big, one is really all you need.

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7 responses to “Not-quite-a-thousand feet

  1. Hi Seabrooke – I really enjoyed this post, and thanks for bringing Bev’s Burning Silo to my attention. There are a couple of features about millipedes that I find most interesting:

    1) the segments with 2 pairs of appendages are actually derived from two primitive segments that have fused during the course of evolution into a single segment (diplosegment). Further evidence of this is seen if one examines their internal organs, certain of which (such as the excretory organs, or nephridia) are also paired. It is thought the diplosegment condition evolved in conjunction with their burrowing habits, which is made more efficiently by having alternate segmental joints rigid and incompressible.

    2) A second feature – also seeming to have evolved in conjunction with their burrowing habits – is the presence of calcium salts in their cuticle. This is unique among terrestrial arthropods and apparently adds considerable strength to their cuticle while at the same time minimizing the cuticular weight and bulk that are required by burrowing arthropods in other groups such as insects.

    Anyway, nice writeup and fantastic photos (as usual). Regards — Ted

  2. That is the last time I lean against a tree at night without first turning the flashlight on it.

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  6. Too much or too little or no body fat would possibly disrupt production of reproductive hormones, that can reduce your sperm count and increase your proportion of abnormal sperm. You’re possibly to provide tons of high-quality sperm if you maintain a healthy weight.

  7. I believe this species has hydroquines, not chemical you described, as a protectant. They are held in sacs on each side of the millipede, which sacs are normally closed by a valve. Surrounding the valve is a muscle that can open and emit the protectant, either at a localized segmant or at all segments (if all are activated). The front section of this millipede does not have the sacs. In Ithaca, NY, i have read, there is an unknown predator of this species that eats only the head section, leaving the rest of the body behind…it is up to this time unknown what this predator is, or whether it is strictly local. there are parasitic wasps that prey on millipedes like this but i’m not sure about their range. There is also a larval form of an insect that injects millipedes up by their head section with digestive fluid quickly, paralyzing them, then retreats for a few hours to return to consume the internal contents of the millipede. The digestive fluid does not dissolve the defense sacs, and what is left is the exoskeleton and the sacs, with the muscle around the sacs dissolved and digested as well. This is in, I believe, Florida.

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