Many scientists quest to discover new species for their entire lifetimes, and still never get to name a novel animal. Mike Newman, an amateur fossil collector, accomplished this amazing feat accidentally. While on a walk through Stonehaven in northeast Scotland to scavenge for fossil fish, Newman stumbled upon an incomplete fossil of an ancient millipede. Though he did not know it at the time, this fossil was actually the oldest known living terrestrial animal, beating the previous record by over 20 million years. This species, now called Pneumodesmus newmani (after Newman) lived approximately 400 million years ago, back when plants first left the water to colonize land.

 

Fossil millipede, Pneumodesmus newmani.

This unassuming rock actually contains the oldest land animal ever known, the Pneumodesmus newmani. Photo by EOL Deep Time Group (Flickr).

 

Even though millipedes have been around for a long time, there are still many misconceptions about them. For example, the name ‘millipede’ comes from the Latin roots milli meaning thousand and ped meaning foot. This has earned the animal the nickname ‘thousand leggers.’ Despite this name, not one identified individual has even approached 1000 legs. In fact, the leggiest millipede (and animal) in the world has only 750 legs! Most adult millipedes have less than 100 legs and can even have as few as 22 legs. Born with only three pairs of legs, millipedes add new legs during molts (growth of the body and shedding of the now too-small outer shell) that occur in underground chambers. These chambers protect the invertebrate from predators during their vulnerable molting period. After many molts, adult millipedes finish with anywhere from 22 to 750 legs (11 to 375 pairs of legs).

 

Millipede on a mossy log.

This living fossil can be found in moist locations in forests, such as leaf litter, on mossy logs, or on protected tree trunks. Photo by David Dennis (Flickr).

 

This leg mishap leads to another common problem: untrained eyes mistaking millipedes for centipedes. Centipedes, or ‘hundred leggers,’ also suffer from miscounting – they often do not have 100 legs. In fact they can have anywhere from 30 to 354 legs (15 to 177 pairs of legs). Because each Order has a variable number of legs, which aren’t reflected by their names, identification can be tricky. However, when looking at other characteristics, the difference between centipedes and millipedes becomes readily apparent.

 

Millipede infographic.

Infographic highlighting key characteristics of millipedes. Photo by Subash BGK (Flickr), cropped by Kit Straley. Infographic by Kit Straley.

 

Centipede infographic.

Infographic highlighting key characteristics of centipedes. Photo by Alan Davey (Flickr), cropped by Kit Straley. Infographic by Kit Straley.

 

Millipedes and centipedes can be differentiated by their behaviors, such as their defenses. Centipedes are predators – when they are faced with danger, they quickly run away. If fleeing isn’t an option, they can use their predatory venom to defend themselves. Millipedes, on the other hand, are quite slow and venom-less. Instead, they have developed numerous ways to keep themselves safe without moving at all. First, they can use their hard exoskeleton (outer shell made of tough material). When millipedes sense danger, they curl up into a ball protecting their soft underbelly.

 

Alternative images of the same millipede, 1 in which it is curled and 1 in which it is not.

The same individual, in its defensive curled up position vs. its normal posture. Photo by John McCullough (Flickr).

 

Bristles are another unique defense mechanism used by one species of millipede. The species, found in Europe and North America, detaches its bristles on the mouthparts and antennae of an attacking ant. Naturally, the ant tries to clean the bristles off. This action actually hurts the ant more because the strands have barbs that hook in. This method works on ants and other predators like centipedes, spiders, pseudoscorpions, and beetles.

 

A bristle-covered millipede.

This species of millipede, Polyxenus lagurus, uses its bristles as a defense mechanism. Photo by Andy Murray (Flickr).

 

Millipedes can also release noxious chemicals to ward off predators. These chemicals can function as irritants, repellents, or antifeedants (chemicals that harm predators once consumed). Certain millipedes have even evolved a coordinated release of two compounds that interact to form cyanide gas! This gas kills attacking arthropods, but can also be produced in high enough concentrations to kill small vertebrates.

 

Millipedes, like many other prey animals, use bright red or yellow patterns to warn predators that they are toxic to eat. This is called aposematic coloring. In order for the eat-me-and-die! signal to work, predators have to be able to see it. Members of one group of millipedes, the Motyxia, are nocturnal. Their predators cannot detect color differences during the night, so Motyxia have instead evolved to glow in the dark! This bioluminescence (production of visible light by a living thing) serves as an alternative warning to predators.

 

Glow in the dark millipede.

A member of the Motyxia group A) during the daylight, and B) without light. (Figure 1 from ‘Bioluminescent aposematism in millipedes’ by Marek et al. 2011).

 

Despite the numerous defense mechanisms that millipedes possess, these creatures are often a tasty meal for other animals and a vital link in the food web. Luckily, millipedes lay between 20 and 300 eggs at a time and are able to maintain high numbers. Their ability to produce so many young, combined with anti-predator behaviors, might explain how they’ve managed to stick around for so long.

 

By: Kallin Lang

Feature photo by: Tanner Nygren, BLM New Mexico, Flickr.


 

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