Two legs good, 750 legs better!

November 17, 2012 • 9:15 am

Alert reader Michael called my attention to an article and video about the world’s leggiest animal. The species is a millipede found in Northern California, lllacme plenipes, and was first described in 1926, and has up to  750 legs. It’s also sexually dimorphic, so males are smaller and have fewer legs.

As LiveScience reported in 2006:

Over the course of three trips to the California Floristic Province, scientists found four male specimens and three females, which they report in the June 8 [2006] issue of the journal Nature.

The females, as in turned out, were not only longer at about 1.3 inches, but also had up to 666 legs. The males averaged 0.6 inches in length and walked on no more than 402 legs.

The males and females probably start out at the same size. Females grow larger and develop more body segments, explained the report’s co-author Paul Marek of East Carolina University. “They are also wider.”

That report gave a record of 666 legs, suggesting that this animal was the work of Satan.

Here it is:

A white millipede named lllacme plenipes (Latin for “the pinnacle plentiful feet”) and found only in a small area of Northern California sports 750 wiggling legs, making it the “leggiest” animal known. (Here, the entire millipede with penny for scale.) CREDIT: Paul Marek

But a LiveScience piece this November 14, reporting a new study by Paul Marek et al. in ZooKeys (reference below), shows that reanalysis of more individuals of this species has shattered the leg record—up to a whopping 750! And there are other oddities:

“It basically looks like a thread,” lead study author Paul Marek, a postdoctoral entomologist at the University of Arizona, told LiveScience. “It has an uninteresting outward appearance, but when we looked at it with SEM and compound microscopes, we found a huge, amazingly complex anatomy.” (SEM stands for “scanning electron microscopy.”)

A rudimentary fused mouth with no known function is among the oddities, as are hairs on its back that produce a silklike product. “There was this huge amount of neat detail that we’re just scraping the surface of,” Marek said. [See Photos of the Bizarre Millipede]

A rudimentary mouth with no function? (See below for a photo). How does it eat?

The millipede wowed researchers with its unusually complex build that was tucked into such a tiny package — it measures 0.4-1.2 inches (1-3 centimeters) long. Shown here, view of the head and mouthpart showing a triangular tooth-lined orifice (arrow). Photo by Paul Marek

I’ll confess that I haven’t read the 35-page paper, as I’m off to the UK today, but I’ve scanned it and present this animal for your delectation.

Here’s a scanning electron microscope (SEM) photo of the legs of a male from the paper:

16 Ventral view of segments (♂). a Lateral tergal and pleural carinae jagged, pronounced on midbody segments b Pleurite medial margin broad, with scaly carina c Postgonopodal tarsus with thinner claw and without bifurcation, but with stout seta. Scale bar 0.4 mm. (From the paper).

Why so many legs? The authors offer an adaptive hypothesis in the abstract:

Based on functional morphology of related species, the extreme number of legs is hypothesized to be associated with a life spent burrowing deep underground, and clinging to the surface of sandstone boulders.

Well, that’s pure speculation, and do they really need that many legs to live in such a niche? Wouldn’t 700 do? Other constraints may have operated here: selection could have been for a thin creature of great length, and the number of legs could simply be a byproduct of genes making the animal longer.

Its head and antennae (see more photos here, or in the paper):

Figure 8.
Lateral (right) view of antennal and cephalic apices (♂). a Scanning electron micrograph: arrow, denticulate shelf-like carina, projecting dorsally from labrum-epistome margin. Scale bar 0.1 mm b Line drawing: top arrow, shelf-like carina; middle arrow, triangular tooth-lined orifice; bottom arrow, gnathochilarium. Scale bar 0.01 mm.

And finally, a video of the beast. Note how large its antennae are relative to its head (shown also in the photo above), and how it’s constantly using them to feel its way about, as expected from a fossorial (underground) animal:


Marek, P. , W. Shear, and J. Bond. 2012. A redescription of the leggiest animal, the millipedeIllacme plenipes, with notes on its natural history and biogeography (Diplopoda, Siphonophorida, Siphonorhinide). ZooKeys 241:77-112. 

21 thoughts on “Two legs good, 750 legs better!

  1. Might I be forgiven for expressing a hope that somebody will engage in a bit of unnatural selection in an effort to produce the first millipede actually worthy of the name? It’s 3/4 of the way there already….


  2. William Shear and Jason Bond have also done some great arachnology work over the years. I love the way this creature shows the evolvability associated with the segmented body plan of arthropods.

  3. This is an excellent example of one of my rules for living: I do not willingly share my home with any animal whose natural complement of legs is less than two* or more than four**.

    *A conditional exception is granted for human microbiota.

    **Preference given to purring things (Note: in the past, I have been able to induce purring in human females).

  4. Thank you for taking the time to post these pictures, plus the information.

    Very very educational.

    Of course, it’s from California!! We’ve got glaciers, extreme heat (Death Valley) the highest point in the Lower 48 (Mt Whitney, been there twice), from which you can see the lowest point in the USA (again, in Death Valley) the oldest plant, and tree, as well as the largest, tallest tree (Sempervirons).

    Thus it only follows that the creature with the most legs would be found here…:)

  5. How does it eat?

    Good question. The paper says on this:

    “Given that the mandibles appear stylet-like, and assuming the mouthparts are moveable, a functional hypothesis for feeding is that the gnathochilarium hinges open, the mandibles are
    protruded to pierce plant and/or fungal tissue, and then the tooth-lined mouth is used
    to suck out the fluid contents. The teeth and labral comb could serve to filter particulates
    exceeding a certain size. Other Colobognath millipedes with somewhat reduced
    mouthparts, for example species of the family Andrognathidae, feed on fungus or other
    live plant or soft organic matter (Gardner 1974). Manton (1961) described the feeding
    of captive siphonophorids Siphonophora portoricensis Brandt, 1837 and Siphonophora
    (=Siphonocybe) hartii (Pocock, 1894) and observed individuals probing decayed vegetation
    with their beaked proboscises, after tapping the material with their antennae.

    Fungi were not observed associated with I. plenipes, as they are often with species
    of Platydesmida. However, live plant tissues, especially fine grass roots that are often
    confused with I. plenipes, were abundant where specimens were encountered and are a
    potential food source.”

    Then follows a portion on how the long and “regularly spiraled metenteron” indicates a water or nutrient-poor diet, but puts as an alternative a long trunk as a store for additional eggs consistent with the sexual dimorphism. So not conclusive either.

  6. “Check out the gams on that lllacme plenipes!”

    “She’s sure a long drink of protoplasm.”

    “The hairy back is kind of a turn-off, though.”

  7. …the number of legs could simply be a byproduct of genes making the animal longer.

    Indeed, what else could it be? Surely nobody thinks the number 750 is coded digitally in the genes. It must be the result of some developmental process that adds segments.

    Wouldn’t 700 do?

    Apparently not. Since there are four legs per segment and neither 402, 666, nor 750 is divisible by four, there must be a segment at the head end with only two legs (perhaps the antennae are the missing two). So it seems 700 is not a possible number of legs.

    I wonder if these critters ever accidentally tie themselves in knots. The one in the video came pretty close to doing so.

    1. Nice observation re possible #’s of legs. And I, too, was wondering if the critter in the vid was practicing its bowline…

  8. This sounds like the kind of post where Larry Moran would react with his usual rejection of adaptationist explanations.

    1. I won’t speak for Larry Moran, but I would happy to endorse such a critique– and, better yet, to hear it rebutted: What if the multitude of millipede legs on that being happen to be the result of a gene duplication or other mutation that affects expression and elaboration of segmental cell/organ fate? Is the continued existence of such a creature prima facia evidence that a greater number of legs confers greater fitness?

      Seems like a stretch to me, but I’m in the minority camp that thinks genetic drift should be the null hypothesis whenever a trait is described and discussed in an evolutionary context. Show me the evidence that a 750 leg phenotype is more fit than a variant that has just 700 and I’ll buy-in to the model but absent that evidence I will default to the “sh!t happens” scenario.

  9. I have read an short article “NOT EVERYTHING HAS A REASON” that answer the question “why do spiders have eight legs” from the website of Washington State University.I think it is the same answer to the “why do millipedes have hundreds legs”:”They just do. There is no WHY.”
    Link here:

  10. Any basis for the speculation that the Millennium Prize in mathematics now includes — along with the Riemann Hypothesis and the Poincaré Conjecture (solved) — the problem of how much Lloyd’s of London would charge to insure the legs of an lllacme plenipes the way it did for Twentieth Century Fox in the 40s for Betty Grable’s?

  11. I just want to point out it’s Illacme (that is, starting with an i), and not lllacme (with three Ls, as you’ve spelled it everywhere but in the reference).
    Sans-serif harms.

  12. A small note: the area in “Northern California” identified in the original article is less than half the distance from Los Angeles to the Lost Coast and Eureka, truly northern California.

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