Ever Seen One Of These Spider “Scarecrows”? Spiders Make Them To Keep Predators At Bay

We recently reported on a new discovery about those zigzags you see in spider webs. Silken decorations like these are known as stabilimenta, and they can serve all kinds of purposes. 

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In the case of the zigzags, it’s thought they may act like extra doorbells, letting you know when food has arrived to a broader range of the web, no matter where you, a spider, are currently standing. Now, another kind of stabilimenta has been described, but these ones aren’t just a bunch of lines, oh no. 

With a central "body" and eight "legs", scientists have confirmed they are decoys made by smaller spiders to look like larger spiders. Yup, turns out spiders are really out here making little scarecrows.

There’s been talk of spider decoys for decades, but until now, they had never been formally documented in the scientific literature. Now, it’s been officially described in a paper outlining the decoy-building skills of two geographically isolated species of Cyclosa, a genus of orb-weaving spiders.

They’re known by another (rather ungenerous) name: trashline orbweavers. A nickname inspired by their love of gathering bits of dead bugs and plants and incorporating them into their webs.

To explore if some curiously spider-like designs could be considered decoys, scientists conducted field research at two geographically isolated locations: Peru and the Philippines. The first lot of images was collected in 2012, while further sets of observations were conducted in 2014 and 2022.

The resulting images revealed that both Peruvian and Philippine Cyclosa species were creating stabilimenta out of prey carcasses and plant material that had a central “body” with lots of linear protrusions. The number of stabilimenta legs varied from five to eight. So, why bother to put in all that attention to detail?

“During a predation attempt, it is likely that concealment inside its spider-like stabilimentum by the Philippine species would be beneficial to the spider by allowing it to escape detection until the predator abandons its attack,” explain the authors.

“The Peruvian species, on the other hand, perches on the web directly above its spider-like stabilimentum and, to the human eye, appears as a small projection relative to the larger structure. The spider may be attempting to direct potential predators toward the stabilimentum and away from itself, escaping by abandoning the web in the event of a predation attempt.”

Not so bad for a “trashline” spider, huh? The stabilimenta may even serve as a double defense in looking a bit like bird poop, something we see is an effective deterrent in many species. As for what’s motivated this silken artistry, that’s something the scientists say will require further research.

“It remains an open question what specific selective pressures have driven these particular populations or species to evolve such complex, unique ‘spider-like decoys’ while other species in the genus have maintained different ‘decorative’ patterns or none at all,” write the authors. “Perhaps there is particularly strong selection from predation within both of these groups that has resulted in increasingly complex visual defense.”

The study is published in the journal Ecology and Evolution.