As soon as John Midgley got back to camp and opened the small jar, he knew he had found something incredible.

In the light of the crackling fire in southeastern Angola, the entomologist examined a strange-looking tarantula he’d just captured. A large, slightly squishy horn sat squarely on the animal’s back.

Midgley is not a spider expert, so he messaged photos of his find to his collaborator, Ian Engelbrecht at the University of Pretoria.

“Ian accused me of Photoshopping the pictures,” quips Midgley, of the KwaZulu-Natal Museum in South Africa. (Read about a new tarantula species found at high altitude.)

So he went out the next night and found several more tarantulas with the same large horn.

“I knew then we had discovered a new species. It’s rare to know you have something special so early in the process,” he says.

The team named the new tarantula Ceratogyrus attonitifer, from the Latin for “bearer of astonishment,” and published their results this week in the journal African Invertebrates.

Fishing for spiders

Following a 26-year civil war that ended in 2002, Angola’s biodiversity remained largely a mystery—no one knew how much had survived.

In 2015, the National Geographic Society and an international team of scientists launched the Okavango Wilderness Project to survey and protect this important and underappreciated region. The project invited several experts, including Midgley, to come to central and eastern Angola to discover what species lived there. (See a 360-degree video of Okavango wildlife.)

In November 2016, Midgley was traversing Angola looking for insects as well as spiders, scanning the ground for signs of his multilegged friends.

In a grassy seasonal wetland surrounding a lake in Angola (Midgley didn’t say exactly where to prevent the theft of these tarantulas for the pet trade), he identified a series of inch-wide holes going almost two feet straight into the ground. (Get an inside look at the illegal trade in tarantulas.)

View Images The C. attonitifer shows his fangs and rears back in a defensive posture. Photograph by Kostadin Luchansky

To see if anything was living inside, he inserted a blade of grass. Immediately something tugged on the end. He returned that night, and as soon as he felt a bite at the other end, he slowly pulled the tarantula out of its burrow.

“It was a lot like fishing,” Midgley says. “If you don’t hold on tight, they can pull the grass right out of your hand.”

Ambush predator

The large horn on the tarantula’s back immediately classified it as a member of the genus Ceratogyrus. Many spiders in this group have similar protuberances, but they are much smaller and harder. The flap on the back of C. attonitifer is as long as its abdomen and is fatty rather than muscular. (Watch a tarantula shed its skin in a time-lapse video.)

Scientists know very little about the new spider—including how it uses its horn—but they do know that C. attonitifer is a nocturnal ambush predator, sleeping during the day in the bottom of its burrow while spending nights at the entrance, waiting to pounce on insects and other prey.

The spider uses venom to kill and dissolve its victims, slurping up the nutritious insect soup after the venom has done its work.

World's Weirdest: World's Biggest Spider With a leg span nearly a foot wide, the goliath bird-eater is the world's biggest spider. And it has a special defense mechanism to keep predators from considering it as a meal.

Particular homebodies

Although Midgley found ten burrows in the 300 square meters surrounding his campsite—a high density for a predator—he only found the species surrounding one particular Angolan lake.

“Baboon spiders are really particular about where they live,” says Heather Campbell, an ecological entomologist at Harper Adams University who wasn't involved in the study. “Baboon spider” is a generic term for subfamily of tarantulas native to Africa. “One species might make its burrows only in one type of sand, another might build next to a particular type of rock.”

If their habitat is disturbed, these spiders can’t just move on. This, combined with their long life spans and low reproductive rate, makes this newly discovered species vulnerable. (Get more facts about spiders.)

This kind of basic biodiversity research goes a long way to cracking the mysteries of the Okavango.