What I Learned Hunting Decoy-Weaving Spiders In The Amazon

Unraveling a mystery about a spider that makes spider-shaped decoys in its web.

A Cyclosa spider and its decoy on the left; a close-up of the spider on the right. Lary Reeves

TAMBOPATA, PERU — In a remote area of the Peruvian Amazon lives a type of spider with a peculiar habit: It builds a spider-shaped “decoy” in its web out of dead insects and other detritus, and which resembles an arachnid much bigger than itself. The idea is that these spider-shaped web additions scare away predators, but nobody knows for sure. Only discovered less than two years ago, scientists know little about these marvelously strange web-weavers, so when I got an opportunity to go to Peru and learn more about them–amongst other bizarre animals that reside here–I booked a flight from New York without a second thought.

The spiders live near the Tambopata Research Center in Peru’s wild Madre de Dios region. To get here you have to fly through Lima to Puerto Maldonado, a rambling mining town through whose streets run an anguished torrent of motorbikes, with single motos improbably carrying entire families at a time. Then it’s a 45 minute bus ride to the town of Infierno (translation: “hell”), followed by a seven hour boat trek up the Rio Tambopata.

Once you pass the Malinowski ranger station, where visitors must sign in, civilization drops away for good, with caimans and capybara (the world’s largest rodent) taking up stations on the banks. Along the way, you enter the Tambopata National Reserve, which covers more area than the land mass of Rhode Island and is one of the most biodiverse places on Earth, with, for example, more than 1,200 butterfly species alone.

Welcome to the jungle

When I arrive at the center, more than 60 hours after my flight left the states, I meet Lary Reeves, a University of Florida entomologist and graduate student I’ve come to follow around. Lary wears a white shirt with a smattering of small holes, sports heavy stubble, glasses, and a head lamp–275 lumens, strong enough to spot an Amazon bamboo rat from a football field away, easy–who’s just returned from a walk to find spiders. His enthusiasm is palpable. With him is Aaron Pomerantz, a graduate student from Florida who has come for 10 days to help gather data on spiders, who is friendly and inclusive. “Welcome to the jungle,” Reeves says. We all share a Cusquena, a ubiquitous Peruvian beer that nevertheless tastes delicious, before going to see a fist-sized tarantula that lives in a nearby hole.

The next day, we set out into the forest. A five minute walk away, we find the first decoy, a relatively well-made one that looks like spider, albeit with six legs. Upon getting close, the web’s inhabitant pulls some strings and makes the spider-like decoy appear to waggle, in a kind of dance. The spider is a puppeteer.

During the eight days that I am here, Reeves and Pomerantz locate and photograph scores of these spiders, and I helped find a few too. To spot one, you walk slowly through the jungle with your headlamp beam on, even at high noon; the canopy darkens the forest more than you’d expect, and the light helps pick out the delicate white webs and their salt-and-pepper decoys. Along the way you slog through a chorus of different sucking and slurping mud varietals, and if you get too close to the river you can sink knee-deep. Luckily when this happened to me, Pomerantz was there to lend a hand. The air is thick with moisture, leading to a perpetual but not unpleasant sense of perspiration, real or perceived, but it is not overly hot. Even though it’s the beginning of the dry season, it rains on and off most of the days of my stay.

The decoy-building spider is thought to be a species in the genus Cyclosa, and Reeves and colleagues plan to formally describe the species, though it remains nameless. This Peruvian Cyclosa species was found in September, 2012, by entomologist Phil Torres. Six months earlier while researching butterfly diversity, Reeves discovered a similar spider in the jungles of the Philippines that likewise makes spider-shaped decoys in its web, albeit of a slightly different shape. The two only found out about each other’s discoveries months later, and now Reeves has shifted his research to the Peruvian Cyclosa, since, among other reasons, it is easier to get to–all things being relative. Earlier this year, filmmakers found another species in Madagascar that appears to make a decoy in its web. And there is another species called Cyclosa mulmeinensis that makes pseudo-decoys, although these blobs are not as convincing or impressive as those of the newfound spiders. The finds are the first of their kind; this behavior hadn’t been previously recorded.

“Why this is going on on separate continents and hasn’t been reported until [recently]–I have no idea how people have not done this before,” says Reeves, who is also a graduate fellow with the National Science Foundation.

Many questions, some answers

I’ve come here with many questions, some of which I have a vague idea about, having followed the story since its inception; as to others I am clueless. But a good place to begin: Why do the spiders build these decoys in the first place? The working hypothesis is that these spider shapes fool and scare away damselflies, which feed on small spiders but avoid larger ones. These insects, in the family Pseudostigmatidae, are the largest damselflies in the world. To the untrained eye, they resemble dragonflies.

“Our working hypothesis, which we plan on testing, is that the Cyclosa makes a decoy spider that is larger than the size of spiders Pseudostigmatids will take, thereby gaining some protection from being eaten by these spider specialists,” says Ola Fincke, a collaborating researcher at the University of Oklahoma and “the world expert on helicopter damselflies,” as Reeves puts it.

Over the course of my trip, and Reeves’s month in the jungle, he goes about laying the groundwork to test this hypothesis, and makes several interesting discoveries. First, Reeves devised a method to collect the webs (which he doesn’t want to share in detail for proprietary concerns) that he will use in the future to collect the animals and their silken firmaments and expose them to damselflies. The idea is to see if the winged creatures pluck more spiders from webs where the decoys have been removed–that would provide evidence that the decoys are indeed meant to scare off the insects.

“It’s not the spider itself, it’s evolution–that’s the amazing thing.”

A big part of the trip has also involved the seemingly mundane task of photographing the spiders and their webs. But it is in the painstaking work that discoveries emerge–and hanging out with Reeves and Pomerantz, who are mad for understanding the intracices of animal life here, especially the infinite strangeness of small beasts like spiders–nothing seems banal. There are also a seemingly endless variety of animals to spot and identify, and distractions provided by visitors like macaws. At one point an ornery, curious scarlet macaw flies onto Reeves’s shoulder, and begins gnawing at the tooth of a Spinosaurus aegyptiacus (a type of dinosaur) on his necklace. I can’t help but be reminded that these birds are in fact dino descendants, and to hear their depraved calls–hauntingly doleful, or just as often angrily strident–one could mistake them for Jurrasic Park velociraptors.

One afternoon, Reeves and Pomerantz are photographing the spiders, this time back in the “lab,” which isn’t really a laboratory but a messy room full of equipment used by researchers with the Macaw Project, who have been studying the habits and health of the area’s macaws and parrots here at the research center for decades. (The lab’s recesses house such treasures as a sloth preserved in a vat of formaldehyde.)

Pomerantz empties the contents of a vial, containing a Cylcosa and its decoy, onto a white Plexiglass sheet placed between two large wooden seats. Beneath it a flash is perfectly positioned, sitting atop a tarnished metal dish, to ensure optimal distance from the sheet for best photo quality). Reeves takes aim with his Canon 7D, which boasts a powerful macro lens. From time to time Pomerantz gently corrals the spider with the tip of a small paintbrush, to prevent it from running off this white plane so Reeves can get a good shot.


“Wait a second,” Reeves says as he snaps a photo of a spider and zooms in on the camera’s screen. “That’s a male!”

This is a surprise. Before, Reeves and colleagues had only found females making these decoys. In other members of the family Araneidae (the taxonomic family that includes orb-weavers), once males are sexually mature, “they pretty much hang out in the webs of the females” and steal food, rather than making complex webs of their own he adds. And sometimes they become the females food. They are also usually much smaller than females. These male Cyclosa, which can be spotted by their hairy “punching bags,” or pedipalps, are not much smaller than females. The largest females are just under 1 centimeter in length.

There’s another discovery when the pair photographs what they’d thought were spider eggs laying within the decoy.

“Those aren’t eggs,” Reeves says as he zooms in on the photo he’s just taken. “They’re spiderlings.”

“I was going to say–that looks oddly like a spider for an egg,” Pomerantz says.

While it’s not unusual for spiders in this family to lay eggs in their stabilimenta, the technical name for these web decorations, the spiderlings usually make a break for it shortly after hatching. These appear to have hung around for a while longer.

Building webs

To learn more about the web-building activities of this species, Reeves and Pomerantz place a couple in two newly-devised observation boxes that force the spiders to build webs parallel to the clear plastic sides, perfect for viewing by humans. Much to their surprise, one of the Cyclosa spiders builds a spiral “P” shape when the decoy is removed from its web, that looks shockingly like the Peruvian “P” that adorns much of the country’s tourist paraphernalia (and also resembles the tail of this monkey geoglyph found amongst the Nazca Lines). Why they do this remains unknown. Perhaps the spiders are just patriotic.

Reeves has also found out that the spiders don’t tolerate artificial stuff in their webs. Just to see what would happen, he puts glitter (colored blue and orange, representing the University of Florida) into the animals silken home–but the crafty spinster cut out all of that garbage.

When it was first reported in late 2012, the story received a fair amount of attention, and Reeves thinks that’s because of the “romanticized idea behind it,” that “people are thinking these spiders are so clever [that] they’re building these structures that look like larger spiders.”

But it’s not like the spiders are “looking at another spider and designing it based on that–this design is just what has been selected for–in that way it’s ingrained into their DNA and which translates into their behavior,” he says. “Spiders that have these more spider-like-looking decoys are more successful than those who don’t. It’s not the spider itself, it’s evolution–that’s the amazing thing.”

“The spiders are dummies,” Reeves continues, using term he often applies to his beloved arachnids, with bemused affection, “but at the same time they are smart enough to make the decision to know what should and shouldn’t go into that structure. Like when we offered them glitter,” he adds.

Until next time

Soon, my time in the jungle is drawing to a close. On the last night that we are both there, Reeves is still up photographing insects after the electricity in the center has turned off. “I’m going to take a photo, alright?” I say, as to not freak him out by approaching in the dark. He consents and laughs, his attention trained on his insect photo subject. Earlier, he’d been photographing a brightly-colored fungus beetle, for project called Meet Your Neighbors, that’s “dedicated to reconnecting people with the wildlife on their own doorsteps–and enriching their lives in the process,” according to the group’s mission statement.

It will be awhile before Reeves and co. will be able to sort through all of the data and photographs they have collected. When he returns to the jungle before long, he will explore the eating habits of damselflies, to see if and how much Cyclosa‘s decoys protect them. There is always the possibility that the decoys have another function, for example to lure parasites/predators of larger spiders, all the better to eat. But Reeves thinks that’s unlikely.

Only the future will tell. As is often the case with fieldwork, obstacles are an everyday occurrence (for example, time and circumstance didn’t allow for studying “silk-henge,” small webby towers built by an as-yet-unknown type of spider, perhaps to defend eggs against wasps). The team doesn’t yet have a permit to collect the spiders, but is working to get one. “If we had a lab specimen it would go a long way,” Reeves says. Until then, the jungle is an open book, albeit not one that provides easy reading. Reeves–and Pomerantz–will be back.