Nature Notes: In the Shadow of the Carmens: A Journey into the Mountains of Mexico

Apart from the barbed and thorny vegetation, the plains and deserts of West Texas can at times appear still, devoid of life. But a single rain dispels that illusion, as otherwise elusive desert creatures make an appearance.

Millipedes are one of those creatures. Take to a West Texas highway after a storm, and you’ll find you’re sharing the road with hundreds, even thousands, of auburn-colored millipedes on the move.

These West Texas millipedes spend most of their lives underground. But in their burrowing, and in their sojourns on the surface, they play a valuable role in the ecosystem.

Millipedes are arthropods, the group of invertebrates that includes insects, arachnids and crustaceans. They have two pairs of jointed legs on each body segment. Scientifically, they’re “Diplopoda” – the “two-footed.”

Mike Medrano is chief of resource management at Guadalupe Mountains National Park. He’s also the lone diplopodologist – or millipede specialist – west of the Mississippi.

He said millipedes’ roots on the planet run deep. Their ancestors appeared some 430 million years ago.

“Some millipede and centipede ancestors were some of first terrestrial animals,” Medrano said. “There was an about 2-and-a-half-meter-long invertebrate that used to crawl around. They’ve found trackways in New Mexico and different places, so they were around.”

Millipedes rely on moisture. They flourish in forested areas. But millipede species here are adapted to arid conditions.

There are two main groups of West Texas millipedes. “Desert millipedes” – the species Orthoporus ornatus – are typically 6 to 8 inches long and reddish-brown in color. They have about 160 legs. Medrano’s research has focused on a second, less common group – “slate millipedes.” Olive-drab to black, they’re about half the size of desert millipedes.

Unlike their forest-dwelling kin, both these millipedes have a waxy coating, which helps them retain moisture. But the key to their survival is their burrowing skill.

Forest millipedes can live in leaf litter. Here, millipedes must burrow deep for cool, wet conditions.

“The ones in the desert all are what’s called the ‘bulldozer style,’” Medrano said. “So they’ve got all these legs, they’re cylindrical – they kind of put their heads down and use all those legs to just burrow through and bulldoze through the soil.”

Eighteen to 24 inches down, the millipedes create round “crypts,” lined with their own fecal material. The millipedes get the water and nutrients they need from the surrounding soil. Here they spend almost their entire lives.

With brief exceptions. Millipedes are “detritivores” – drawn to the detritus of dead plants.

After a summer rain, they emerge to feast on wet plant material, and to mate. The surface activity is over within a matter of days.

“I’ve seen occasions when you’ll get an intense thunderstorm in the middle of the summer, and they come out, they’re out for three days, and they burrow back under,” Medrano said. “And then when the typical monsoon rains come, they’re not surface active. They’ve done their bit, and they’re down for the wintertime, until the next time it rains.”

As they burrow, millipedes aerate and loosen the soil. And in their forays to the surface, the millipede masses make an important contribution. By consuming quantities of fallen plant material, they return nutrients to the soil.

It take three to five years for a millipede to reach sexual maturity. The entire process takes place underground.

West Texas millipedes rely on a unique form of chemical defense to ward off predators. From glands at the base of their legs, they emit a bitter liquid. The color of iodine, it’s a beta-quinone.

“When they get threatened, they will coil up into a spiral,” Medrano said. “They clamp themselves down, and then they start exuding this liquid. It’s enough for most things to spit it out and move on to something else. Then they uncoil and go about their business.”

The liquid stinks, and can stain the skin, but it’s generally harmless to people. Some do experience irritation or blistering.

Despite their ubiquity, millipedes have received relatively little scientific attention. In his study of slate millipedes, Medrano identified 20 new species. He said research would likely reveal a comparable diversity in desert millipedes.

Millipedes give some people the creepy-crawlies. But their claim to the land is undeniable. Their lineage predates mammals by 200 million years. And if evolutionary history is a guide, they’ll be here long after we’re gone.

Nature Notes is underwritten by the Dixon Water Foundation and is produced by Marfa Public Radio in cooperation with the Sibley Nature Center. This episode was written by Andrew Stuart.