The Mystery of that Stonehengy Rainforest Structure? Solved
Posted by Richard Conniff on December 21, 2013
You remember seeing these bizarre silken rainforest structures reported earlier this year? Each one is a sort of tower inside a web-fenced circular corral, and the result has a sort of Stonehenge-cum-Seattle Space Needle look. But tiny.
The graduate student who first posted photos last summer had no idea what they might be, and his request for help went viral.
Now there’s an answer, from researchers in Peru’s Tambopata Reserve. Here’s part of the report from Nadia Drake at Wired:
For six days, Reeves, Torres, and Hill watched the tiny towers, all the while considering different hypotheses.
They debated whether the structures could have been made by mites (not too likely, given how small the mites are), or if the fluffy, fine silk pointed toward a spider (yes). They questioned whether the sacs were eggs at all. Maybe, Reeves suggested, they were looking at a structure called a spermatophore — a type of gift containing sperm and nutrients that some insects and spiders exchange during mating. Could these structures be the work of the huntsman spiders the team kept seeing on tree trunks? It was hard to say. Every time a hypothesis began to gain traction, another observation would swoop it and kill it.
Finally, on Dec. 16 as the scientists were preparing to leave the rainforest without an answer, two of the eggs hatched and Torres saw two tiny spiderlings running around the base of the structures. “We were excited about that but still hesitant,” Torres said, noting that most of their hypotheses so far had fallen through.
But the next day, a third egg hatched and produced another small spider. “That really confirmed it for me,” Torres said. “Anything we saw crawling in there had to have come out of the structure.”
Now, even though the team is sure that they’re looking at some kind of intricate spider nursery, they’re still confused. For starters, a spider laying only one egg in a particular spot is exceptionally rare. “Traditionally, the female will lay a bunch of eggs, wrap it up very well, sit, and protect it,” Torres said. “This is kind of the opposite.”
And the amount of parental investment in the structures is immense, considering the single spiderling inside.
Then there’s the question of the spider’s identity. It could be a jumping spider – the spiderlings’ body shape resembles the Salticidae family, and they have two giant eyes, resembling a jumping spider’s adorable head. But the rest of their eyes aren’t quite in the right place.
It’s also possible the structures could be the work of a spider with a dark side. Near some of the clusters, the team saw several spiders that camouflage their nests with the corpses of their prey, such as ants and smaller spiders. Could the small spiderlings grow into these crazy corpse spiders? We’ll have to wait and see, as Torres and his colleagues continue their investigation.
My hunch is that the corral-like fencing is a defensive structure, to keep off ants or other species that might menace the young spider. On the other hand, the biggest threat probably comes from parasitic wasps, and it’s not clear how this structure would be much help against them.
And in other spider news: On top of yesterday’s report that the diabolical looking vampire squid is actually just a scavenger, now comes a study saying that spiders, those ultimate sit-and-wait predators, may actually get a quarter of their diet, like Birkentstock-wearing health food coop holisitic medicine enthusiasts, by eating pollen.