Diplopoda: The Not-So Creepy Crawlies

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By Jackson Means (mjacks4@vt.edu) and Derek Hennen (dhennen@vt.edu)

Millipedes (Fig. 1) are one of those insect-like creatures that you’re likely to encounter in your garden on a regular basis, and toss aside as just another natural oddity you would rather not look at too closely. One could not be blamed for this reaction; millipedes do frequently produce chemical defenses that can smell quite powerful and have a few too many legs to remain in the comfort zone of most people. This really is a shame, as millipedes are one of the most fascinating and diverse groups of animals on the planet. Plus, some of those chemical defenses smell like cherry cola, which is pretty cool.

Figure 1: Ptyoiulus, one of our common native millipedes. Photo by Derek Hennen.

Figure 2: A pauropod in the family Eurypauropodidae. See the Twinkie resemblance? Photo by Corey Husic, Taken from Bugguide.net: https://bugguide.net/node/view/603392/bgpage

Let us begin with the taxonomic placement of millipedes (where they fit in with the rest of the tree of life) and some basic biology. The millipedes (Class Diplopoda, meaning paired feet, more on that later) are in the subphylum Myriapoda (meaning 10,000 feet, which is highly inaccurate) along with Chilopoda (centipedes), Pauropoda (pauropods) and Symphyla (garden centipedes). Those last two are extremely tiny and obscure, but if you ever see a millimeter-long Twinkie with branched antennae then you have likely found a pauropod, and if you ever see a four millimeter long, thin white creature with long, quickly moving antennae then you likely have a garden centipede (which are fairly common in garden soils, Fig. 3). Centipedes are familiar to most anyone who gardens, but do your best to avoid them, as the larger Scolopendromorpha (Fig. 4) and Lithobiomorpha (Fig. 5) can deliver a nasty bite. In general, however, when you uncover a centipede, it will quickly dart out of sight.

Figure 3: A symphylan, which can often be found running about waving their antennae in the soil. Photo by James C. Trager, taken from Bugguide.net: https://bugguide.net/node/view/382493/bgpage

Figure 4: Scolopocryptops sexspinosus, a commonly encountered centipede that can bite with its powerful venom jaws, visible in this image just below the head. Photo by Derek Hennen.

Figure 5: A stone centipede (Lithobiomorpha), so-named for their propensity to hide under rocks. Photo by Derek Hennen.

So, how do you tell a centipede from a millipede? Both have lots of legs and are rather linear in appearance, but one will simply curl up and hide while the other will immediately run away from you. The most notable difference is in the number of legs. While centipedes have a reasonable one pair of legs per body segment, millipedes have, over evolutionary time, fused every two body segments into what are called diplosegments, which means that they now have two pairs of legs per body segment (Fig. 6). You may think that having double the legs would translate to double the running speed, but actually the opposite is true. While the relatively few-legged centipedes are swift to enhance their predatory capabilities, millipedes are slow, and use their multitude of legs to aid in burrowing through the underbrush. Furthermore, millipedes are detritivores, meaning they only eat decaying organic matter such as leaves and wood, which, combined with the aeration their burrowing provides for the soil, makes them fantastic helpers in the garden.

Figure 6: A diplosegment of a euphoberiid millipede, chosen for this blog post because of its awesome spines. Photo taken from Wikipedia commons: https://pl.wikipedia.org/wiki/Euphoberiidae#/media/File:Archipolypoda_Cross-section.jpg

Appalachian Millipedes

Appalachia is one of the most diverse areas in the world for millipedes, likely due to the presence of innumerable moist, dark gullies, which millipedes love. Additionally, the Appalachians were a refuge for many groups of animals during the last ice age, staying fairly constant in terms of weather and temperature. This allowed animals to diversify, such as the plethodontid salamanders and our friends the millipedes. Due to this diversity we will not cover each of the over 1,000 millipede species found throughout the Appalachians, but rather focus on some major groups you are likely to encounter: starting with the most common and going to some of the more bizarre millipedes.

Order Julida, Families Parajulidae, Blaniulidae & Julidae

First up is the order Julida, of which the Ptyoiulus from figure 1 is a member. These millipedes are commonly called “snake-like millipedes,” due to their cylindrical body plan. Ptyoiulus (pronounced Tie-you-lus) is a member of the family Parajulidae, are an inch or so long, and typically purple or orange in color, with dark spots along their sides. Males have a greatly enlarged first leg pair, which they use to hold onto females during mating. They’re most often found in deciduous leaf litter, and are an understudied family. Unfortunately, some of the members of the Julida found in the Appalachians have been introduced from Europe, such as the families Blaniulidae and Julidae. Blaniulidae are white and quite thin, often with red circles down their body—showing off the structures where their defensive chemicals are stored (Fig. 7). The Julidae are about half an inch long, typically brown or black, and have striations around their body rings (Fig. 8).

Figure 7: Blaniulus guttulatus. The red spots may be quite pretty, but they indicate where B. guttulatus produces and excretes its harmful chemicals (harmful for ants, not so much us). Photo by Tom Murray, taken from Bugguide.net: https://bugguide.net/node/view/31941

introduced millipede

Figure 8: Cylindroiulus, an introduced millipede from Europe who is quite handsome with its gold rings. Photo by Derek Hennen.

Order Spirobolida, Family Spirobolidae

Next, we have the order Spirobolida, family Spirobolidae. This family contains Virginia’s most recognizable millipede: the giant American millipede (genus Narceus, Fig. 9). These millipedes can grow up to 6 inches long, and sport a beautiful blackish-blue color with orange-red highlights along the back of each body ring. They are excellent burrowers, great mothers (she provisions each egg with a fecal pellet to pass on helpful gut microbes), and workhorses of the undergrowth. If disturbed, they may secrete their defensive chemicals, which will discolor skin like an iodine stain. We’re lucky to have this millipede across the state!

ironworm

Figure 9: The ironworm, Narceus americanus. These can often be found climbing trees throughout the Appalachians. Photo by Derek Hennen.

Order Spirostreptida, Family Cambalidae

This family contains the regal millipedes, genus Cambala (Fig. 10). They are long and thin, typically purple or cream-colored, with impressed crests down their body rings. They have a linear patch of eyes on their head, and a constricted “neck” behind their head that aids with identification of this genus. They are most often found under logs in moist areas such as gullies and near streams.

Figure 10: Cambala minor. These often can be found in large numbers buried face first in acorns. It’s fairly adorable. Photo by Derek Hennen

Order Callipodida, Family Abacionidae

This family contains the brown crested millipedes in the genus Abacion (Fig. 11). They have a light brown stripe down their bodies at about “shoulder” height, and have pungent chemical defenses. If you disturb one of these, you’ll be smelling the consequences for a while! They can survive better in drier areas than many other millipedes, and can be found in leaf litter and under rocks and logs, often hanging on to the underside of them.

Figure 11: Abacion, quite possibly the worst smelling millipede. Photo by Derek Hennen.

Order Polydesmida, Family Euryuridae

Found in association with deciduous logs, the genus Euryurus has three orange spots on its back that accents its purple-black base pattern (Fig. 12). It has a square-shaped epiproct (“tail”) that differentiates it from other Polydesmida in our area. This family fluoresces under UV light and has a spicy cherry kick to its chemical defenses!

Figure 12: Euryurus, a beautiful genus of millipedes which can be found in late August hiding in rotten wood. Photo by Derek Hennen

Order Polydesmida, Family Paradoxosomatidae

This family was introduced into North America from Asia, and can be separated from our native Polydesmida by the dorsal transverse groove on each body ring. In Virginia, you will often find Oxidus gracilis in both disturbed habitats and seemingly pristine ones, unfortunately (Fig. 13). It is a brown to dark black millipede with yellow paranota (dorso-lateral extensions of the body ring) about ¾ of an inch long. It appears to outcompete our native millipedes in some areas, and has an unattractive smell.

 Oxidus gracilis

Figure 13: Oxidus gracilis, the worst millipede. Photo by Derek Hennen.

Order Polydesmida, Family Polydesmidae

A native family, the Polydesmidae in Virginia are represented by two common genera: Pseudopolydesmusand ScytonotusPseudopolydesmus species are generally a little over an inch long and sport pleasing pink coloration, with Pseudopolydesmus canadensis showing off with a bold black line down its back, flanked by brick-red paranota (Fig. 14). Scytonotus is less common and about a centimeter long, and is sometimes called the velvet millipede, due to short hairs on its back that give it a velvety appearance up close. These millipedes are found in leaf litter and under logs, and males have beefier legs that are used to hold onto females during mating.

Figure 14: Pseudopolydesmus canadensis, a commonly encountered millipede that just so happens to be the specialty of D. Hennen! Photo by Derek Hennen

Order Polydesmida, Family Xystodesmidae

This family contains some of Virginia’s most beautiful millipedes (Fig. 15), commonly known as the cherry millipedes, due to their chemical defenses (hydrogen cyanide and benzaldehyde) that smell like cherries. Many of these millipedes will also fluoresce under UV light (like the Euryuridae), and they exhibit bold color patterns, including black and yellow patterns with stripes or spots to warn predators of their poisonous defenses. They’re harmless to people and make excellent subjects for photography. They’re often seen during the spring and fall, and common genera in Virginia include Apheloria, Appalachioria, Rudiloria, Pleuroloma, and Nannaria.

Figure 15: The cherry millipede, Apheloria virginiensis corrugata, produces an incredible amount of cyanide, and may form the basis of multiple mimicry rings with several genera of xystodesmid millipedes. Photo by Derek Hennen.

Order Chordeumatida, Family Cleidogonidae

This order of millipedes lacks chemical defenses, with its species instead relying on speed and camouflage to stay safe. Our most common family is the Cleidogonidae, with the genera Cleidogona and Pseudotremia. Cleidogona is found in leaf litter and is brown with white spots (Fig. 16). When uncovered, they quickly flee into the duff. Pseudotremia is more uncommonly seen, but can be found in caves and in moist leaf litter. Uncommon families you may see in this order include: the Conotylidae, which look similar to the Cleidogonidae, but are darker and have more prominent hairs and swollen knobs around their “shoulders.” They are most active in the winter, when few people are on the lookout for millipedes. The Striariidae have their first body ring modified into a hood that covers most of their head, and have longitudinal crests on the rest of their body rings. Small and brown, they are easily overlooked in the leaf litter. The Trichopetalidae are minute (~5mm long) white millipedes found in leaf litter and under logs. They have long hairs on their backs and secrete a sticky glue-like substance for defense. The Buotidae are even smaller white millipedes found in southwest Virginia. Found in leaf litter and under rocks, they look like small fungal roots and are easily overlooked (Fig. 17).

Figure 16: Genus Cleidogona, an extremely widespread and diverse genus with multiple species found only in caves throughout southwest Virginia. Photo by Derek Hennen.

Buotus carolinus

Figure 17: Buotus carolinus, one of the rarer millipedes encountered in southwestern VA. Buotus is so rare, in fact, that this species is listed as a species of concern for the state. Photo by Derek Hennen.

Order Platydesmida, Family Andrognathidae

Sometimes called “feather millipedes,” Virginia has two genera: Brachycybe (western Virginia) and Andrognathus, which is more widely distributed in the state. Brachycybe are subsocial salmon-pink millipedes and are found under logs, where they gather in groups to feed on fungi, often in a pinwheel formation. Interestingly, males exhibit parental care of eggs. Andrognathus are quite thin and brown in color, and are also found under logs (Fig. 18).

Figure 18: Andrognathus corticarius, sometimes called the dirty noodle millipede, is semi-social and often found on the underside of logs. Photo by Derek Hennen.

Order Polyzoniida, Family Polyzoniidae

Some of the strangest millipedes are the Polyzoniidae: the slug millipedes, slow-moving creatures found in leaf litter and under rocks. Our Virginia species are in the genus Petaserpes, Greek for “broad creeper” (Fig. 19). They have small, triangular heads and are cream-colored. When prodded, they release their chemical defenses, which smell like camphor.

Petaserpes cryotocephalus

Figure 19: Petaserpes cryotocephalus, a slug millipede that smells like camphor but probably should not be rubbed on your chest to relieve congestion. Photo by Derek Hennen

Order Polyxenida, Family Polyxenidae

And finally, one of the most bizarre millipedes are commonly known as bristly millipedes. These are minute (~4mm long) millipedes that are most often found under tree bark or stones (Fig. 20). They are covered in long hairs, and have a tuft of barbed hairs posteriorly which they use for defense. When an ant attempts to bite down on these fluffy balls of quills, the hairs detach, piercing the cuticle of the ant and gumming up its jaws, causing desiccation and frequently death. Some tropical ants, however, have evolved to specifically prey upon bristly millipedes, using their large branched mandibles to strip the millipedes of their quills (Fig. 21).

bristly millipedes

Figure 20: Polyxenus, the bristly millipedes, are common in the old world, and the jury is still out on whether our Virginia species is native or introduced from Europe. Photo by Derek Hennen.

Figure 21: Thaumatomyrmex ants use their incredible mandibles to remove the defensive hairs of polyxenid millipedes. Photo taken from Wikipedia Commons: https://commons.wikipedia.org/wiki/File:Thaumatomyrmex_mandibularis_casento173039_head_1.jpg 

Conclusion

The Diplopoda is an impressively diverse taxon, with around 12,000 described species and many more left to discover. We are working hard to describe new species and understand how these species relate to one another, and we are slowly but surely filling in the puzzle that is the tree of life, one multi-legged piece at a time.

 

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