What Created This Mysterious “Picket Fence” in the Amazon?

It’s probably the only picket fence in the Amazon, but scientists have no idea what made it or what its purpose might be.

Georgia Tech doctoral student Troy Alexander stumbled upon these two-centimeter-long white structures growing on trees in Peru on June 7.

The picket fence of the Amazon. Photograph courtesy Troy S. Alexander, Tambopata Research Center

Since then, the intricate handiwork has baffled scientists. Although most agree it was likely built by an insect, no one can identify the species that built it, or what the fence might be protecting.

“I thought anything this distinctive would have been discovered already,” Alexander said.

“I’ve talked to researchers worldwide and haven’t found an answer, so I don’t feel crazy saying that I’ve found a new species, or at the very least, a new behavior,” he said.

“What Is That?”

Alexander made the discovery when he was volunteering at the Tambopata Research Center as part of the Tambopata Macaw Project. He noticed something unusual on one of the blue tarps the group was working under for shade. (Read more about a new species of decoy spider that was discovered at Tambopata.)

“I looked up and thought, ‘What is that?’” Alexander said. “At the time, I thought a Urodid moth had started building a cocoon and then just got distracted and didn’t finish or got eaten.”

Alexander in the Peruvian Amazon. Photograph courtesy Troy S. Alexander, Tambopata Research Center

Intrigued, Alexander snapped a few photos to show an entomologist back at the center. But the expert had never seen anything like it. Neither had anyone on Reddit’s What’s This Bug group, where Alexander also posted the photo.

Soon after, he saw several more of these structures, which consist of a tall, white conical post in the middle, surrounded by what can only be described as a small, circular white picket fence.

Having spotted several, Alexander knew that this wasn’t just the efforts of a distracted moth. He posted these new photos on Reddit and got a few suggestions, but nothing conclusive. Alexander’s leading hypothesis—one proposed by a Reddit reader—is that the structure was spun and built by a spider instead of a standard web. (Also see “Photos: World’s Biggest, Strongest Spider Webs Found.”)

Instead of spinnerets, or silk-spinning organs, some spiders have what’s called a cribellum, which, instead of spinning silk fibers, pushes the molecules through a fine mesh.

“Looking more closely at the photos, I thought, yeah, that does make sense. It does look like the silk was just pushed through a mesh,” Alexander said.

Unveiling the Mystery Builder

Alexander, who’s working on his Ph.D. in natural drug discovery, said he intends to stick with his chosen field, even with the glut of attention he has received from his Amazonian discovery.

The mystery object is less than an inch long. Photograph courtesy Troy S. Alexander, Tambopata Research Center

He added he’d like to go back to Tambopata, although he doesn’t have plans to return in the immediate future. Luckily though, an entomologist will be traveling to the research center this winter to try to identify what’s building the forest fences.

When asked what he would name his find if it proved to be a new species, Alexander said he would need to learn some Latin so he could incorporate the word for “fence” in the name.