Flat-Backed Millipedes: All You Need To Know

This article will be your guide to everything you need to know about flat-backed millipedes.

Flat-backed millipedes are of the order Polydesmida. They are named such because most of the species within the order have keels on each of their body segments.

These flat structures are known as paranota and give them a flattened look.

In the following article, we will discuss this peculiar millipede, what it eats, its life cycle, mating rituals, and more.

What Are Flat-Backed Millipedes?

Millipedes are small insects of the class Diplopoda. They have two pairs of legs at the bottom of each of their body’s segments.

Polydesmida, or the flat-backed millipedes, are the most significant order among millipedes.

The flat-backed millipedes appear to be flat because of their flared body segments. This is in contrast to other species of millipedes that look cylindrical.

Flat-backed millipedes look a lot like centipedes. They are usually brown, and their size is between 0.6 inches and 1.0 inches.

Unlike centipedes, which are carnivores, these millipedes feed on decaying plant matter and are not very harmful to animals or humans.

Flat-Backed Millipede Types

There are several families within the broader spectrum of flat-backed millipedes.

Xystodesmidae millipedes are a family of flat-backed millipedes that have bright colors like yellow, orange, or red in combination with black or brown.

Other species in the flat-backed millipede family include:

The yellow and black flat-backed millipede.
The eyed flat-backed millipede.
The common flat millipede.
The brown flat-backed millipede.

What Does A Flat-Backed Millipede Eat?

Flat-backed millipedes are vegetarian and prefer eating roots and fruits like strawberries. In fact, they are detritivores, i.e., organisms that feed on dead and decaying organic and plant matter.

Hence, the flat-backed millipede’s diet consists of decaying plant material such as dead leaves, decaying fruit, and roots, among other things.

Several species among the flat millipedes also feed on decaying wood of trees like deciduous and conifers.

Where Do Flat-Backed Millipedes Live?

Flat-backed millipedes are usually found crawling in damp habitats such as among leaf litter, under rocks, and barks.

You may also spot them in compost pits or among decaying plant matter since that is what they feed on.

Flat-backed millipedes are also found in the cracks of tree stumps, barks, and logs. You can spot them in loose soil.

Geographically speaking, flat-backed millipedes are found in the United States from southeast Alaska to Monterey county, California, and even the Sierra Nevada mountains.

They are also very commonly found in northwestern Europe and the UK.

Life Cycle of A Flat Backed Millipede

Flat-backed millipedes have two breeding cycles – one from late spring to summer and the second from late summer to mid-fall.

The adult males mate only once. They will court the females by secreting a pheromone or chemical that will attract them to breed.

The males also make certain squeaking sounds with their legs to attract the females.

Mating happens when the males release a sperm sack that finds its way to the female’s reproductive organs.

Now when it comes to flat-backed millipedes, the females store the sperm and reproduce at least a couple of batches of eggs.

This happens once during the spring season and once during the summer.

Each egg is laid in a capsule in the soil. The young millipede will usually molt once inside the egg before hatching a couple of months later.

If the temperature outside drops and the atmosphere is cold, the young millipede will overwinter until the climate is suitable enough to hatch.

Once hatched, the larvae of the flat-backed millipede gradually develop and mature into their adult form over the years.

It could be quite a while before it reaches complete maturity and is ready to mate. Young millipedes usually look like tiny versions of adults.

As they grow, they develop more body segments and legs.

According to what has been observed, flat-backed millipedes will survive for about 7-10 years.

Mating Rituals of Flat-Backed Millipede

Reproduction in millipedes was, for years, shrouded in mystery. But scientists have finally figured it out.

In most species, the legs of the males, called gonopods, transfer packets of sperm into the females and carry out reproduction.

While male millipedes of this species mate only once, the adult females of the flat-backed millipedes store sperm from a single mating.

They then use this stored sperm to reproduce many batches of eggs.

However, other species, like the pill millipede, reproduce by releasing a sperm packet from behind the male’s head.

This is then passed on to the female till it reaches the female’s reproductive organs. The male bristly millipede, on the other hand, weaves a web and deposits the sperm there.

The female then moves into the web to transfer the sperm to her reproductive organs.

How Long Do Flat-Backed Millipedes Live?

According to research, millipedes usually live for 7-10 years. How long the flat-backed millipede lives for cannot be said with certainty.

However, since millipedes live for 7- 10 years, it can be considered that flat-backed millipedes, too, would survive for ten years.

Do They Bite?

Millipedes do not bite. When threatened, millipedes will usually coil their bodies to stay safe. However, they do release a toxin to keep potential predators at bay.

If you come in contact with this toxin, it can irritate your skin if you are allergic.

Are They Poisonous/Venomous?

Millipedes are not poisonous or venomous, but they secrete a toxin when threatened that could harm their predators.

But because of the small size of the millipede, the quantity of the toxin they secrete is very little, causing no potential harm to human health.

However, if you are allergic to millipedes, it can cause irritation, itching, or redness.

Are They Harmful or Beneficial to Humans?

Millipedes are beneficial in the sense that they act as recyclers when they feed on decaying plant matter. However, they are not harmful to humans at all.

They usually do not bite or sting. They are not poisonous or venomous and, therefore, can cause no harm to humans or pets.

What Are Flat-Backed Millipedes Attracted To?

Flat-backed millipedes usually feed on dead and decaying plant matter. Hence they are attracted to damp, moist, and dark environments.

You will usually spot them among leaf litter, inside loose soil, in and around swimming pools, compost piles, flower beds, etc.

How To Get Rid of Flat-Backed Millipedes?

Using pesticides is an effective short-term solution to get rid of flat-backed millipedes. However, the better solution would be to prevent attracting these insects.

One significant way to do that is by keeping the surroundings clean. Regularly clear the debris and mulch. Don’t let leaves litter in moist heaps for long.

Prevent water accumulation anywhere in and around the house. Seal pest entries to your home so they don’t find a way inside through holes or cracks.

Also, avoid over-watering your garden and plants and mow the grass closer to the ground.

You could also turn to chemical control to prevent a pest problem.

Interesting Facts About Flat-Backed Millipedes

Flat-backed millipedes communicate with fellow insects and millipedes through the secretion of pheromones and scents.
Among all other species of millipedes, flat-backed ones have longer legs. They also use legs to attract females during mating season.
Although millipede means a thousand feet, flat-backed millipedes are shorter than other species and have only 40 legs.
Flat-backed millipedes are detritivores. This means that they feed on decaying and dead organic and plant matter.
Flat-backed millipedes tend to release hydrogen cyanide when threatened. While this is a toxin because the millipede is so tiny, the amount it secretes is practically harmless unless you are allergic to the insect.

Frequently Asked Questions

Are flat back millipedes poisonous?

No, flat-back millipedes are not poisonous, although they may emit a corrosive or choking liquid when threatened.
These secretions, which come from organs near the tail, can burn or irritate the skin of anyone who touches them.
To avoid any issue, it is best to simply leave them alone rather than handle them directly.

What are flat-bodied millipedes?

Flat-bodied millipedes are a type of arthropod found in forests and other wet environments.
They range in length from about 0.4 to 2 inches and feature flat, oval-segmented bodies that are often red, brown, or black.
These millipedes eat decaying organic matter found in soil and leaf litter and play an important role in the ecosystem by helping to break down forest detritus into nutrient-rich soil.
They also have modified legs with very fine bristles that help them travel smoothly over soft surfaces such as fallen leaves and mosses.

What do flat-backed millipedes eat?

Flat-backed millipedes primarily feed on decaying plant material and small insects.
They use their mouthparts to tear apart and consume the food, turning it into easily digestible pieces with their powerful jaws.
They also consume some fungi and bacteria that exist in leaf litter, which helps them better absorb nutrients from the food they eat.
Most flat-backed millipedes will search for and consume plants that are recently dead or injured, like newly fallen leaves or tree bark.

Where do flat-backed millipedes live?

Flat-backed millipedes are primarily found in moist, dark places such as leaf litter, under logs and stones, in soil, or in decaying organic matter.
They are commonly found in deciduous forest habitats like the forests of the eastern United States and Canada but may also be distributed across all continents except Antarctica.
Additionally, they may inhabit wooded suburban backyards. They generally reside on or near the ground, under objects that provide shelter from the elements.

Wrap Up

Flat-backed millipedes are a species of millipedes belonging to the order Polydesmida.

They are also sometimes called keeled millipedes because of the flat structures on their backs that make them appear flat instead of cylindrical.

These millipedes do not bite or sting. Even though they release a toxin when threatened, they’re not poisonous or venomous and cause no harm to humans or animals.

Thank you.

Reader Emails

Over the years, many readers have asked us to identify this insect and sent us pictures and descriptions of where they found it.

We have tried to capture some of the letters below and the discussions we have had with our readers. Please go through it!

Letter 1 – Flatbacked Millipede

millipedes
Trying to id this millipede from pa in the poconos.

This is a Flatbacked Millipede in the order Polydesmida. That is the best we can provide at the moment.

Update: (01/20/2008) Millipede IDs
Here are ids. for the millipedes on the millipede page. Most are quite old; don’t people submit new ones more often than this? (07/03/2007) PA. Poconos. Sigmoria (Rudiloria) trimaculata trimaculata (Wood) (Polydesmida: Xystodesmidae)
Rowland Shelley
North Carolina State Museum of Natural Science

Letter 2 – Mites on Flat Backed Millipede

Flat backed millipede riders Hi, I know this is a flat backed millipede, but what are those mites riding on it? Maybe you could ask Barry M. O’Connor for me? I snapped this photo on 06/11/06 in Port Orchard, WA – he’s about 2″ long. Many thanks, Kevin PS – that big bug from ‘toe biter’ that you never identified – the bug in a jar that died at school? It didn’t die from the stress of being at school, but probably from the stress of not being in water as it is a water beetle.

Hi Kevin, We will post your letter and try to get the answer you requested. We can’t seem to find the letter you cited. Please give us a page and date. Barry OConnor Responds: Hi Daniel – The division of the dorsal plate on the back of the mites on the millipede, and the smaller size of the posterior part indicate that these are deutonymphs (last immature instar) of the family Parasitidae. Despite their name, parasitid mites are not parasitic, merely riding on their host from place to place. The name dates to an 18th century misperception by the French naturalist Latreille who observed these mites on a beetle and thought they were parasitic and named them “Parasitus”. The rules for naming animals require that the first scientific name given to an animal is the one we use, even if it turns out not to be appropriate. These mites normally inhabit rich but patchy sources of organic matter like manure or carrion where they feed on nematodes or fly eggs/larvae. It’s rather surprising to see these on this millipede; they’re much more commonly seen on scarab, carabid & silphid beetles that frequent such substrates. Others are specific inhabitants of the nests of small mammals and bumblebees, and their deutonymphs ride on those hosts. Other parasitids live in the soil and prey on other microarthropods but don’t use other animals to disperse since their habitat is more continuous. Glad to help – you always have cool pictures! All the best! – Barry Update: (01/20/2008) Millipede IDs 6/12/06 . Port Orchard, WA. Probably Chonaphe sp. (Polydesmida”: Xystodesmidae), as they seem too wide to be the ubiquitous Harpaphe haydeniana . Rowland Shelley North Carolina State Museum of Natural Science

Letter 3 – Flat Backed Millipedes

centipedes
Hello folks, I hope all is well. On a hike at a local conservation area I photographed this mass! Is it centipede larva? Take Care, Janet from Dundas, Ontario

Hi Janet,
According to BugGuide, these Millipedes are in the order Polydesmida, the Flat Backed Millipedes. Sometimes the aggregate after rains.

Update: (01/20/2008) Millipede IDs
9/19/05 . Apheloria virginiensis corrugata (Koch) (Polydesmida: Xystodesmidae), 1 adult plus juveniles.
Rowland Shelley
North Carolina State Museum of Natural Science

Letter 4 – Flat-Backed Millipede

hope it doesn’t bite!!!
Hi Bugman!
LOVE your site. I’ll be visiting a lot! Can you tell me what this beast is? I can’t tell if it is a centipede or a millipede. He was scurrying across our patio here in Apex, North Carolina. Thanks!
Nancy Nice

Hi Nancy Nice,
The difference between Millipedes and Centipedes is that Centipedes have one pair of legs per segment and Millipedes have two pairs of legs per segment. We couldn’t locate a species name for your Millipede, so we contacted Eric Eaton. Here is his response: “It is a flat-backed millipede (Polydesmida order). Very pretty, but many species like this secrete a cyanide compound to defend themselves. As long as you don’t eat one or lick it, you should survive.”

Update: (01/20/2008) Millipede IDs
6/9/05 . Apex, NC. Apheloria tigana Chamberlin, 1939 (Polydesmida: Xystodesmidae)
Rowland Shelley
North Carolina State Museum of Natural Science

Letter 5 – Flatbacked Millipede

Harpaphe millipede? Sat, May 2, 2009 at 12:02 PM Dear Identifiers of Insects, This time I’m writing about a huge millipede that keeps attempting to cross a heavily-trafficked footpath; I’ve rescued him twice, and am wondering what type he is. Sort of looks like a picture I found online of ”black and yellow millipede” or ”Harpaphe” genus, but the legs on that were black, not yellow. This fella is a good three inches long, and rather hefty as far as bugs go! Certainly the largest millipede I’ve ever seen. Thanks! Hope you find the photo interesting! R. Thompson

Yellow Spotted Millipede — Flatbacked Millipede

Dear R. Thompson, Your submission to our website did not use our newly formatted form that requests a location, so we have no idea where this Millipede was found. This also means that you have written to our site before. We hope you write back with your location. We believe you are correct that your Yellow Spotted Millipede is in the genus Harpaphe, probably Harpaphe haydeniana, The following remarks are according to BugGuide: “this particular millipede secretes a dark fluid that has an odor similar to the almond extract used in cooking. Apparently this is a defensive manuveur. Millipedes also curl up in tight coils when threatened. (1) Caution: Many millipedes with bright color patterns secrete a compound containing cyanide. Wash your hands after handling them and do not allow children to pick them up. ‘Millipedes are entirely non-toxic to humans and can be picked up by hand. Some secretions discolor the skin, but this wears away in a few days without lasting effect. Some large, cylindrical, tropical species squirt their defensive secretions up to a half meter (2-3 feet) and can blind chickens and dogs. Their fluids are painful if they get into the eyes, and persons working with tropical millipedes should be suitably cautious.’ ~Rowland Shelley Harpaphe is in the tribe Xystodesmini.” Sorry about that – the location of the millipede is Chapel Hill, NC. I didn’t pick him up with my hands, but let him crawl onto a stick. Thanks for the info! Excellent. An eastern species is Sigmoria trimaculata, and it has yellow legs. You can also see photos of this species posted to BugGuide and there are reports of representatives of the genus from North Carolina. Update: April 13, 2017 Based on new research and a new submission, we now believe this is Apheloria tigana, thanks to BugGuide where it states: “‘Apheloria tigana is the dominant xystodesmid millipede in central North Carolina, particularly the “Triangle” (Raleigh, Durham, Chapel Hill region). Individuals typically have yellow paranota (lateral segmental expansions on the dorsa), a yellow middorsal spot on the anterior margin of the collum or 1st segment, and yellow middorsal spots on the caudalmost 3-5 segments. In central NC south of the Deep/Cape Fear Rivers there is a different and undescribed species with yellow middorsal splotches on essentially every segment.’ – Roland Shelley, North Carolina State Museum of Natural Sciences.”

Letter 6 – Flatbacked Millipede

Subject: Correctly identified a millipede on my own? Location: Columbia, TN March 16, 2013 9:11 pm I just wanted to share my favorite critter find of the day today. Found March 16, 2013 in Middle Tennessee in a heavily wooded and mossy area. I believe based on my searching of this site that it is a Sigmoria trimaculata, however, since I am usually wrong in my assumptions, a confirmation would be appreciated. Feel free to share my photo as I did not see very many on here. Thanks for all that you all do! Signature: S Carter

Flatbacked Millipede: Sigmoria trimaculata

Dear S. Carter, We agree with your identification. Back in 2007, we posted an image of a Flatbacked Millipede that we identified only to the order level of Polydesmida, but a year later, Rowland Shelley of the North Carolina State Museum of Natural Science identified it a Sigmoria trimaculata. His comment at the time was: “Most are quite old; don’t people submit new ones more often than this?” We don’t get images of this interesting Millipede that often, so your photos are a great addition to our archive.

Letter 7 – Flatbacked Millipedes

Subject: Three red and black bugs found! Location: Missouri, U.S.A. April 1, 2016 5:44 pm I would like your help on identifying three orange and black stripped bugs. I was in my yard searching for bugs, so I lifted up a rotting log and to my excitement I found three cool looking bugs all near each other! Pretty please with cherries on top help me identify them!

Signature: Gracie S.

Dear Gracie, These are Flatbacked Millipedes in the order Polydesmida, a group well represented on BugGuide.

Letter 8 – Multicolored Centipede and Flat-Backed Millipede

Subject: Centipedes? Location: Southern California May 16, 2016 6:37 pm Image #1 was in the hallway at work, in my office in Santa Ana, CA on May 13, 2016 Baby Centipede? Image #2 (deceased) was taken as I entered my weekend retreat in Cherry Valley, CA. About a week earlier. I’m assuming is some type of centipede as well. Just wondering if either one is dangerous? Signature: Thanks so much!! Betsy

Dear Betsy, The critter you found in your office is a Flat-Backed Millipede in the Order Polydesmida, which is pictured on BugGuide. The other image from Cherry Valley is a Multicolored Centipede, Scolopendra polymorpha. According to Charles Hogue in Insects of the Los Angeles Basin: “The bite of this species may be painful. Although there are no data on the effects of its poison on humans, it is probably harmless. Contrary to popular belief, the sharp claws on the legs are not poisonous, although the last pair of legs is capable of pinching.” According to BugGuide, the common names are Tiger Centipede and Common Desert Centipede.

Letter 9 – Flatbacked Millipede

Subject: What is this? Location: Southern Ohio June 18, 2016 4:02 pm Found this creature in the woods, curled up in a ball. (Was around 1:30 in June). Signature: Fallistar

Dear Fallistar, We identified your colorful Flatbacked Millipede as Apheloria virginiensis corrugata on BugGuide where it states: “Caution: Many millipedes with bright color patterns secrete a compound containing cyanide. Wash your hands after handling them and do not allow children to pick them up. ‘Millipedes are entirely non-toxic to humans and can be picked up by hand. Some secretions discolor the skin, but this wears away in a few days without lasting effect. Some large, cylindrical, tropical species squirt their defensive secretions up to a half meter (2-3 feet) and can blind chickens and dogs. Their fluids are painful if they get into the eyes, and persons working with tropical millipedes should be suitably cautious.’ ~Rowland Shelley”

Letter 10 – Flatbacked Millipedes from British Columbia

Subject: Is this a Sawfly larva? Location: South Surrey, BC, Canada July 24, 2016 12:18 pm Hi Bugman, I came upon several of these in my garden in South Surrey, BC, Canada in June, 2016. South Surrey is south of Vancouver, BC, near White Rock, just north of the USA border (WA State) — just in case your readers aren’t familiar with the local geography. I had no idea what they are, but I think they look like your photo of a Sawfly larva. Are they harmful to plants or beneficial insects? Thanks for your help. Signature: Jerry Steinberg

Dear Jerry, These are NOT Sawfly larvae. They are Flatbacked Millipedes, Harpaphe haydeniana, and according to BugGuide: “This particular millipede secretes a dark fluid that has an odor similar to the almond extract used in cooking. Apparently this is a defensive manuveur. Millipedes also curl up in tight coils when threatened. Caution: Many millipedes with bright color patterns secrete a compound containing cyanide. Wash your hands after handling them and do not allow children to pick them up.” According to Island Nature: “the millipede can perform its duty as a ‘macroshredder,’ breaking up plant material and initiating the process of nutrient recyclying [sic] in the soil ecosystem … . In fact, it plays such an important role in the process that it can be considered to be a “keystone” species.” Thanks so much! Keep up the GREAT work! Jerry

Letter 11 – Flat Backed Millipede

Subject: Sigmoria Trimaculata Location: Briceville, tn April 1, 2017 10:03 pm My husband found this little fellow along a creek bank in Briceville, TN this evening (04/01/2017). Approximately 3″ in length. Am I correct in identifying it as Sigmoria Trimaculata? Signature: John and April

Dear John and April, Alas, we have not the necessary skills to identify this Flat Backed Millipede to the species level. It certainly might be Sigmoria trimaculata (please note the first letter of the second word of the species name is lower case), based on this BugGuide image, but it also looks quite similar to this BugGuide image of the Appalachian Mimic Millipedes in the genus Brachoria. According to BugGuide, the family Xystodesmidae contains many similar looking species. You might be correct, but we cannot confirm that for certain.

Letter 12 – Flatbacked Millipede

Subject: Is this really Sigmoria trimaculata? Location: North Carolina April 11, 2017 7:27 am Hi, Searching around I found an older letter that had a yellow-legged black millipede in North Carolina (2009/05/03/millipede-3/), but both the letter-writer’s photo and the photos on the Bug Guide page for Sigmoria trimaculata showed yellow markings on the back of the millipede as well (especially the latter!). The millipede that I found looks completely solid black on the top/back, with only its legs and… leg-plates-joiny-bits?… being yellow. I couldn’t find any Wikipedia page about Sigmoria trimaculata to look up whether this might just be a juvenile, or a subspecies, or something like that — do you know if it is the same species? If so, why is it plain black on top? Signature: S.

Dear S., We are generally very reluctant to state a Flatbacked Millipede is a definite species, but your individual looks very much like Apheloria tigana which is pictured on BugGuide where it states: “‘Apheloria tigana is the dominant xystodesmid millipede in central North Carolina, particularly the “Triangle” (Raleigh, Durham, Chapel Hill region). Individuals typically have yellow paranota (lateral segmental expansions on the dorsa), a yellow middorsal spot on the anterior margin of the collum or 1st segment, and yellow middorsal spots on the caudalmost 3-5 segments. In central NC south of the Deep/Cape Fear Rivers there is a different and undescribed species with yellow middorsal splotches on essentially every segment.’ – Roland Shelley, North Carolina State Museum of Natural Sciences.” Hi Daniel, Thank you for the response and the link! I guess they are the sort of creature where species identification is generally rather tricky? But that does look exactly like my fella — much appreciated

Yours, S April 14, 2017 (So in the last two days, I’ve been seeing quite a few of these critters curled up on the sidewalk in the harsh daylight where I’ve never seen ’em before, seemingly unable to move even when I nudge them to a grassy area — not at all like the briskly ambulating specimen that originally caught my eye. It’s a little worrying. The internet says millipedes might migrate in spring and fall, but it’s pretty much already summer hereabouts, and my searches keep coming up 90% about millipede extermination… sigh…) Alas, that is because there are far more people want to eliminate lower beasts from their lives than those who want to learn about them.

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