This Tarantula Species Has a Weird, Deflated Horn on Its Back

Arachnophobes, beware: As Carrie Arnold reports for National Geographic, a newly discovered tarantula species boasts an unusual appendage—namely, an elongated squishy horn planted squarely in the middle of its back—sure to haunt your dreams for the foreseeable future.

Dubbed Ceratogyrus attonitifer, or “bearer of astonishment,” the spider is native to the southern African country of Angola. Although its distinctive horn may seem like an arachnid anomaly, Earther’s Jake Buehler notes that certain members of the Ceratogyrus genus, as well as several unrelated species, wield similarly horned protrusions. Whereas these creatures’ horns are typically small and hard, C. attonitifer’s is long and soft.

John Midgley, an entomologist from South Africa’s KwaZulu Natal Museum, happened upon the unicorn-like arachnid while conducting research for the National Geographic Okavango Wilderness Project, which aims to assess and protect southern Africa’s under-studied biodiversity, in Angola between 2015 and 2016.

According to Arnold, Midgley was out exploring when he spotted a series of small holes extending nearly two feet underground. He poked a blade of grass inside of one and felt the telling tug of an animal responding to the intrusion; later that night, he returned to the burrow and managed to pull the tarantula out of its hiding place.

When Midgley took a closer look at the captured spider, he realized its singularity and immediately sent photographs of it to colleague Ian Engelbrecht, an entomologist at of the University of Pretoria. At first, the entomologist jokes, “Ian accused me of Photoshopping the pictures.” But after Midgley captured an additional seven specimens, the pair realized they had stumbled upon a previously undocumented species.

Midgley and Engelbrecht’s findings, published in the journal African Invertebrates, provide an intriguing overview of the creature’s appearance: As Mindy Weisberger writes for Live Science, the tarantula’s body measures around 1.3 inches long and is covered in short black hairs. Its defining horn, which features a hard base punctuated by a bulbous, “bag-like” body, extends over the back. In living spiders, the floppy part of the horn bloats up similar to a thin balloon, but in deceased specimens, the horn deflates and turns a darker shade.

Significantly, the horn’s biological purpose remains unclear. In an interview with Science Alert’s Tessa Koumoundouros, Engelbrecht explains that spider species with smaller, firmer horns may rely on the protrusion to support muscles “that operate the sucking stomach.”

“Spiders digest their prey externally, dissolving it into a kind of 'bug soup' in their mouth before ingesting it,” Engelbrecht continues. “The sucking stomach acts like a little pump that sucks the soup through the spider's oral cavity and onwards into the rest of the digestive system.”

While scientists posit that solid horns could enable some spiders to strengthen the muscles powering this phenomenon, Engelbrecht says the theory doesn’t apply to the newly discovered species, as its horn is “not solid and muscular.”

For now, the researchers have little to go on aside from observation and information provided by Angolan locals. As Earther’s Buehler points out, the horned spider is new to scientists, but not to the region’s residents, who call the species “chandachuly.” According to these firsthand reports, the tarantula survives on an insect-based diet and inflicts a venomous, though typically not deadly, bite. When threatened, the creature is quick to retaliate, with Midgley and Engelbrecht writing that “any object inserted into the burrow was attacked enthusiastically.”

Brent Hendrixson, an arachnologist at Mississippi’s Millsaps College who was not involved in the study, tells Earther that the discovery speaks to the “pretty incredible diversity” of the Okavango Delta region.

“It’s really exciting to know that there’s so many things out there that we don’t know about,” Hendrixson concludes. “But that’s also part of the problem: that we don’t know much about the diversity that’s out there, and so until we do, it will be incredibly difficult to protect and conserve [wildlife].”

Midgley and Engelbrecht have taken at least one step toward preserving C. attonitifer’s future: As National Geographic’s Arnold writes, the pair declined to identify exactly where the spiders live, as they hope to protect the species from falling prey to the illegal pet trade.

Meilan Solly | | READ MORE

Meilan Solly is Smithsonian magazine's associate digital editor, history.