Some jumping spiders look so much like wasps that scientists named them for the predatory insects.
But University of Cincinnati biologists wondered: Do these mimics really look like insect faces or is it just our own perceptual bias? After all, we see faces everywhere: tree trunks, rock outcrops, clouds.
So when travel restrictions from COVID-19 shut down field research, UC biologists decided to turn to an objective third party, a computer.
They presented digital portraits of jumping spiders, praying mantises and wasps to see if a computer algorithm could identify them correctly from shapes and patterns each contained. And surprisingly even the computer was fooled about 20% of the time.
The study was published in the journal Behavioral Ecology .
"The original idea was inspired by one species, a peacock jumping spider called Maratus vespa, which is Latin for wasp," UC student and study lead author Olivia Harris said.
This jumping spider lifts its abdomen during an elaborate courtship display to reveal a colorful wasp-shaped back. The illusion is made all the more realistic by raising flaps on its sides that give the spider the familiar guitar-pick shape of a wasp's face.
Researcher Jurgen Otto discovered, described and photographed the species in Western Australia in 2015 with co-author David Knowles.
"That got us thinking," Harris said. "Why would a spider want to look like a wasp, which is a predator of spiders, especially as a primary element of its courtship display?"
It turns out that when spiders see distant insect predators, they tend to freeze in place and give their undivided attention to the potential threat. And that attention could give male jumping spiders the opportunity they need to begin courting the female
Researchers used computer vision techniques and machine learning and neural network algorithms to see if artificial intelligence properly classifies images properly as spiders,wasps, praying mantises or flies. The AI got it wrong across all 62 species nearly 12% of the time. And it correctly identified 13 species every time.
But the AI misidentified Maratus vespa and several other spiders more than 20% of the time and typically as wasps. Researchers said the next step would be to test their hypotheses with behavioral experiments with live female jumping spiders.
Deception is not unheard of in animal courtship. Some male moths simulate the sounds of echolocating bats to discourage potential mates from taking flight. And antelopes called topi have been documented warning does of phantom predators to discourage them from fleeing their territories.
"But this is the only case we've found of males mimicking a predator visually," she said.
UC Associate Professor Nathan Morehouse, a study co-author, said the spiders appear to be using sensory exploitation to their advantage.
Morehouse said they found that the predator illusion works best at greater distances or in the female spider's periphery, where she relies on eyes that see only in monochrome green. But once the male gets closer, the female's front-facing, color-discerning eyes take over.
"Females will not be fooled forever. If they were, they would be robbed of the ability to make mate choices, which would put the species at a long-term disadvantage," Morehouse said. "It's beneficial for the males to break the illusion."
