Features

Unlovable Millipedes: Nature’s Ultimate Survivors

By JOE EATONSpecial to the Planet
Tuesday March 02, 2004

The Scottish seaside town of Stonehaven, birthplace of the deep-fried Mars bar, now has a second claim to fame. Mike Newman, an Aberdeen bus driver and amateur palaeontologist, recently discovered the fossil remains of the oldest known land animal there. The half-inch-long creature has been named Pneumodesmas newmani in his honor. Although some might not consider it an honor: P. newmani is, after all, a millipede. 

How do we know it lived on land? It’s well enough preserved to show tiny spiracles—intake vents for air. These would not have worked at all under water. 

Millipedes don’t get a lot of respect or affection. They lack charisma, they’re not cuddly, and most of them smell bad. Many otherwise reasonable people have a strong aversion to them just be cause they have an excessive number of legs. (No millipede has a thousand legs, as you might assume from the name; the champion, a Southeast Asian species, has only 750, or 375 pairs). 

But you have to admire their sheer staying power. P. newmani, recogni zably a millipede, lived 428 million years ago during the Silurian era, when Scotland lay near the Equator as part of the Old Red Sandstone Continent. A lot of flash-in-the-pan lifeforms have come and gone since then, but you can still find creatures a lo t like P. newmani in your flower bed, or in the nearest shady patch of woods. 

The place wouldn’t have looked much like Scotland, though. Sheep and heather had yet to evolve. The barren land had only recently been colonized by algal crusts, lichens, and p rimitive plants like mosses and liverworts. Soil as such was just beginning to develop as these pioneers wore away the rock and added their remains to the first humus.  

Newman’s find may have lived on detritus—dead plant matter—as most millipedes still d o. Its world must have been a kind of arthropod Eden: plenty to eat, no predators. But that didn’t last long.  

Eventually the ancestors of the modern scorpions came ashore and found bountiful hunting grounds. Insects evolved at least 400 milllion years a go, likely from a millipede-like ancestor.(The earliest insect fossil, also found in Scotland, languished in a drawer in the British Museum for 80 years before someone recently recognized it for what it was). Some became formidable hunters as well: dragon flies with the wingspan of a Cooper’s hawk. Then came the first land vertebrates, lumpish toothy horrors. All these would have found the early millipedes fair game. 

Some millipedes, over time, responded by getting big. One line culminated in a behemoth c alled Arthropleura, 6 feet long and a foot and a half wide, likely the largest terrestrial arthropod that ever existed, or could, due to inherent design constraints. You may remember Arthropleura from the coal swamp diorama in the Academy of Science’s Life Through Time exhibit, now somewhere in storage. 

Others went a different route: they got toxic. One such, the clown millipede (Harpaphe haydeniana), inhabits Northern California. It’s striking in its own way, glossy black with a pair of yellow spots on each segment; it has a relatively modest 62 legs. For people with an aversion to both clowns and things with too many legs, this would be a hard animal to love. The coloration is a warning to would-be predators that it’s loaded with cyanide. I’ve never h andled one myself, but the clown millipede is said to give off a definite whiff of almonds. 

In his splendid book For Love of Insects, Thomas Eisner, more or less the founder of the science of chemical ecology, describes his work with a New York millipede, Apheloria, back in the 1950s. (No, millipedes aren’t insects, they’re myriapods. But Eisner’s curiosity transcends taxonomic categories). He verified earlier anecdotal reports that Apheloria did emit hydrogen cyanide, and figured out how its chemical de fense worked. The millipede produces a precursor substance called mandelonitrile, stored in a special reservoir. When threatened, it telescopes its body segments to squeeze the chemical into another chamber containing a catalytic enzyme. The ensuing react ion releases the hydrogen cyanide, which seeps through ducts along the millipede’s side.  

Eisner’s book includes a wonderful photograph of a toad which has just tried to swallow an Apheloria millipede. You wouldn’t think a toad’s face would be capable of much emotional range, but the amphibian’s disgust is palpable. 

The cyanide trick isn’t universal among millipedes. Other species produce benzoquinones. Still another, a chunky, pillbug-like form known as Glomeris, secretes a chemical that sedates predat ors. Wolf spiders that attacked a Glomeris became “motionless, flaccid, and totally unresponsive”, and could take up to 5 or 6 days to recover. The two key chemicals at work here, glomerin and homoglomerin, are quinazolinones, akin to methaqualone, aka Qu aalude. (One of Eisner’s colleagues was able to demonstrate that Quaalude does not knock out spiders, if you were wondering). 

Ground-up millipede was part of the standard pharmacopeia in 17th-century England, along with wolf’s liver, peony root, and stee l syrup. We can only speculate as to what effect this had on the patient.  

In addition to being able to brew poisons and sedatives, some millipedes are luminescent and others fluoresce under ultraviolet light, as do scorpions. No one seems to know what a daptive value this has for the animals. 

Those refinements, though, came long after Pneumodesmas newmani roamed the Scottish tropics. Here’s a salute to that unsung pioneer, or whatever many-legged ancestor first ventured onto terra firma. It was many small steps for a millipede, but one giant leap for animalkind.