In the sticky jungles of South America, a mysterious spider crafts towers out of silk—confounding scientists with its intricate creations.
Comprising a silky spire surrounded by a circular picket fence, the structures are sometimes called "Silkhenges" because of their building material and the abiding mystery of their origin: Not only are the clever spiders still unidentified, no one has ever seen the arachnids actually make these works of art. (See 10 beautiful photos that will make you love spiders.)
Now, a new video of spiderlings hatching from one of the towers collected in Ecuador's Yasuní National Park might provide some clues about these spiders' secret lives.
“This was just such a rare glimpse at these Silkhenges.”
So far, scientists have spotted the silky structures in Peru, French Guiana, and Ecuador, though most have been seen near Tambopata.
There, in 2013, researcher Troy Alexander snapped the first known photographs of the odd fences, which soon went viral.
Scientists were baffled: Had spiders built them? Were they the work of some other silk-wielding insect? A fungus? And what, exactly, was the purpose of those silky fenced towers?
That December, Torres returned to the jungles of Tambopata. Night after rainy night, he and a team scrambled through the dense rain forest, trying to catch something in the act of building the towers. No dice.
Then Torres caught a lucky break: A single translucent orange spiderling crawled out of a silky tower he'd brought back to the research center.
So a spider was the culprit—but which species or genus? A spiderling is too small and undeveloped to make any kind of taxonomic ID. And why the arachnid would go to such enormous lengths for a single egg didn’t make any sense.
Tough Egg to Crack
It still doesn’t. But Torres and colleague Aaron Pomerantz, an entomologist and National Geographic explorer, are hoping the new video will offer some clues.
For one, three spiderlings emerged from the same Ecuadoran tower—not just one, as in Peru.
“I have a feeling that Silkhenge is way more widespread than currently documented, and that having one to a few eggs in there is probably pretty standard—still possibly amongst the lowest amount of eggs per egg sac recorded in spiders,” Torres says.
“If hours and hours of observations can result in this, hopefully it can also result in what we’re all really after—watching an adult make this darn strange thing.”
Finding an adult would help solve the mystery of the spider's identity. Ideally, Torres and Pomerantz would raise any hatched spiderlings into adulthood. If future attempts to grow adult spiders are successful, they could allow the team to finally identify the species—or at least the family the spiders belong to. (All past attempts to raise Silkhenge spiderlings have failed.)
Failing that, the next best thing is to grind up the spiderlings, extract some DNA, and see if the genetic sequence matches a known species.
Pomerantz did that earlier this year, when he sent a particular sequence of spiderling DNA to a genetic barcoding facility in Canada. Turns out, the Silkhenge sequence is an 86 percent match to some known spider families, among them Theridiidae, Clubionidae, and Linyphiidae. But that amount of genetic similarity isn’t good enough to identify a particular species, let alone a genus; humans and fish are equivalently similar. (Check out a new species of spider that looks like a leaf.)
“As far as I can see, the barcoding just confirmed it’s a spider,” Torres says. “This is one darn tough egg to crack.”
So. Many. Spiders.
Other experts say it’s not surprising that a simple DNA barcoding test couldn’t identify the spider.
“Only 10 percent of the invertebrate species are described, and only a few of them are in a DNA database,” says Peter Jaeger, an arachnologist at Germany’s Senckenberg Research Institute.
William Eberhard, of Panama's Smithsonian Tropical Research Institute, agrees.
“The big question from the barcode data,” Eberhard says, “is not whether it is a described or undescribed species—most species from that site are probably undescribed—but which of the already known species is the DNA from this spiderling closest to?”
Pomerantz and Torres are up for the challenge of bulking up the branches of the spider family tree.
“Moral of the story is we continue to try and rear out baby Silkhenge to adults," Pomerantz says, "or sequence more spideys.”