Leggiest Animal: Champ millipede located after 79-year gap

A millipede species with up to 750 legs, the most recorded on any animal, has turned up in its tiny native range in California after decades with no sightings, biologists say.

LITTLE PACKAGES. A rare California millipede, Illacme plenipes (top), may be the world’s leggiest species, but it moves slowly and grows barely as long as an entomologist’s thumb. Scanning electron micrograph (bottom) shows the millipede’s four legs per segment. P. Marek and Bond

The Illacme plenipes millipede has never been found beyond a 0.8-square-kilometer area in San Benito County, several hours south of San Francisco, explains millipede taxonomist Paul E. Marek of East Carolina University in Greenville, N.C. No biologist had recorded seeing it there since its discovery in 1926, even though specialists checked the area several times in recent years.

Last fall, though, Marek and his colleagues found males, females, and youngsters in the original site, Marek and his North Carolina colleague Jason Bond report in the June 8 Nature.

“This is wonderful news,” says millipede specialist Robert Mesibov of the Queen Victoria Museum and Art Gallery in Launceston, Tasmania. “It shows that if we’re serious about conserving biodiversity, we need to pay attention to tiny natural areas.”

“This is the millipede that most closely lives up to its name,” says entomologist Darrell Ubick of the California Academy of Sciences in San Francisco. He has collected arthropods in California for years and looked for I. plenipes—unsuccessfully—several times during the 1990s.

During their studies of arthropod diversity, Marek and Bond had been thinking about I. plenipes. When Marek went to California last Thanksgiving to visit his mother, he recruited his brother Rob to search the old site.

Even though the creature has hundreds of legs, adults are less than 3.4 centimeters long and about half a millimeter wide. “It’s pretty hard to immediately tell the difference between this tiny, threadlike thing and a root hair,” says Paul Marek.

After about an hour of searching on their first day, the brothers realized that one “root hair” was moving. The record-breaking species lived. “I was probably close to hyperventilating,” Paul Marek says.

His luck held up during several return visits, and the brothers and Bond collected 12 specimens, with adults varying in leg number from 318 to 666. Females typically outgrow and outleg males, says Marek, and in this family, millipedes probably add legs throughout their lives.

The new finds don’t top a 1926 I. plenipes specimen or even the 742 legs of a millipede recently found in Tobago.

“The number of legs is insignificant compared to the geography,” says entomologist Richard Hoffman of the Virginia Museum of Natural History in Martinsville, who focuses on that state’s insect diversity. The only other known members of the family containing I. plenipes live in Southeast Asia.

Marek and his colleagues used 21st-century microscopy to fill in details in the old descriptions. The male’s sperm-delivery organs, for example, are “very elaborate” with fringed auxiliary parts, says Marek.

Like other millipedes, the leg champs “don’t sting; they don’t bite; they don’t carry diseases,” says Hoffman. They just convert leaf litter into soil.

However, those mild manners result in little funding for studies of the creatures. “I do millipedes at night and on the weekends,” Hoffman says.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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