New Tarantula Species Has Big, Weird, Floppy Horn

This is a close-up of the newly described tarantula species Ceratogyrus attonitifer, showing the peculiar soft and elongated horn-like protuberance sticking out of its back (Photo: Ian Engelbrecht)

Tarantulas generally stick to a pretty predictable body plan — eight legs, long fangs, usually fuzzy. But a newly-described species of tarantula in the southern African country of Angola has thrown scientists a big curve ball. The tarantula is about as weird as it gets for spiders, sporting a long, pliable, droopy “horn” on its back, and no one’s sure what it’s even for.

The special spider was first collected by scientists as part of the National Geographic Okavango Wilderness Project, which aims to investigate, categorise, and protect the biodiversity in a relatively understudied region of Africa — the Okavango drainage in the nations of Angola, Botswana, and Namibia.

John Midgley, an entomologist at the KwaZulu Natal Museum in South Africa, was in central Angola a few years ago to document local invertebrate species as a part of this effort. It was there that Midgley first encountered the tarantula, and — along with coauthor Ian Engelbrecht, an invertebrate conservation scientist at the South African Biodiversity Institute — described the new species in a recently published paper in the journal African Invertebrates.

Midgley was out collecting insects in Angola’s miombo woodlands when he first spotted the spider’s burrows. At night, he returned and dug out the burrows, retrieving their arachnid architect from the sandy soil.

Midgley immediately realised he had found something unusual. It was a definitely a female baboon spider (a group of African tarantulas), but its appearance was absolutely alien. Sticking out of its back was a ridiculously large horn-like projection, pointed back and flat against its bulbous back segment (abdomen). Even stranger, the growth was all soft and floppy, just sitting there like a deflated balloon, making the spider look like God’s most horrifying early draft of a unicorn.

“I was quite amazed when I saw it, and sent a picture to Ian as soon as I could,” Midgley told Earther, noting that the protuberance was so huge that he and Engelbrecht couldn’t quite believe it. “So, I went out looking for more burrows. I found another two spiders the next day and we then knew that this was undescribed and not just an odd mutation.”

This is an individual of the newly described species (Ceratogyrus attonitifer) in defensive posture (typical for baboon spiders) in its natural habitat. (Photo: Kostadine Luchansky)

After finding more of these baboon spiders with built-in handles, the team was able to formally describe it as a new species, giving it the name Ceratogyrus attonitifer. While the weird tarantula was new to scientists, the arachnid was quite familiar to the people living in that area of Angola. To them, the species is known as “chandachuly” in the Luchazi language.

Local people also provided information to the researchers on the spider’s habits, like its insect-based diet, and its painful (though not dangerously venomous) bite. The researchers also found that the tarantulas were aggressive defenders of their turf, leaping out and attacking any object placed in their burrow.

None of this particularly unusual for a tarantula. But that weird arse horn? Completely unlike anything ever seen before. Midgley says that some other Ceratogyrus species and unrelated tarantulas in the Americas have horn-like projections on their backs, but these are comparatively tiny knobs, and are hard, exoskeletal structures.

“This is the only known species with a soft horn,” explains Midgley. “In general, horned tarantulas are an oddity; this species is one of a kind.”

Scientists don’t really have any idea what the hell the new horn might be for. In other “horned” species, the projections house extensions of the stomach muscles, says Midgley, but the chandachuly’s preposterous windsock is a squishy, empty sack with no muscles inside.

Top view of the newly described tarantula (Photo: Midgley JM, Engelbrecht I (2019))

Brent Hendrixson, an arachnologist at Millsaps College in Mississippi not involved in this study, is impressed by the spider’s unwavering eccentricity.

“It’s clearly different than anything that’s been seen before,” Hendrixson told Earther. He wonders if the horn’s softness is partially linked to its size, since a hardened structure that big might be a hindrance in small burrow spaces.

Hendrixson was happy to see that the authors redacted the location information for where the tarantulas were found.

“When I saw this spider and its remarkable anatomy, the first thing I told myself was ‘I hope they didn’t publish locality information in the paper’,” Hendrixson said. “Folks that are in the pet trade would probably be all over that, because it’s a pretty unique spider.”

Indeed, the illegal pet trade is an existential threat to newly-described and unusual tarantulas. It would be tragic if the chandachuly met the same fate as the Gooty sapphire tarantula, a brilliant, blue spider from India that is now critically endangered and rapidly declining partially from white hot demand in the pet trade.

The publication of site locations has inadvertently aided animal trafficking in a rare Bornean lizard, the earless monitor, so there’s precedent for these risks being realised.

Fortunately for the new tarantula, the Okavango Wilderness Project seeks to set up ecosystem-wide conservation areas, so it will likely receive some significant protections. Midgley says that future research will focus on the spider’s behaviour in the field, as well as whatever that horn actually does.

The discovery is a reminder of how unique this part of the world is, and how much biodiversity is left to unveil in the Okavango catchment. The same surveys that introduced Ceratogyrus attonitifer to the world found two other spider species potentially new to science, and expanded the known geographic ranges of other spider groups.

The newly described tarantula species Ceratogyrus attonitifer, showing the peculiar soft and elongated horn-like protuberance sticking out of its back. (Photo: Ian Engelbrecht)

Hendrixson noted that Angola is sits at the intersection of multiple ecoregions in Africa, so the discovery of “pretty incredible biodiversity” isn’t surprising.

“It’s really exciting to know that there’s so many things out there that we don’t know about,” Hendrixson said. “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 things.”

And conserving things like tarantulas has benefits, even if the big guys aren’t exactly bursting with charm.

“It’s important for people to realise that [spiders] are vital parts of the ecosystem, even if they might not look pretty to us,” Midgley said.

Yes, that even includes the bitey, hairy ones with the creepy dried mango slice on their back.

Jake BuehlerTwitter or at his blog.

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