What do jumping spiders find sexy? How DIY tech is offering insights into the animal mind.
The raccoon smart box
Why are raccoons so good at city living? One theory is that it’s because they’re flexible thinkers. To test this idea, UC Berkeley cognitive ecologist Lauren Stanton adapted a classic laboratory experiment, called the reversal learning task. For this test, an animal is rewarded for learning to consistently choose one of two options, but then the correct answer is reversed so that the other option brings the reward. Flexible thinkers are better at reacting to the reversals. “They’re going to be more able to switch their choices, and over time, they should be faster,” Stanton says.
To test the learning skills of wild urban raccoons in Laramie, Wyoming, Stanton and her team built a set of “smart boxes” to deploy on the outskirts of the city, each with an antenna to identify raccoons that had previously been captured and microchipped. Inside the box, raccoons found two large buttons—sourced from an arcade supplier—that they could push, one of which delivered a reward. Hidden in a separate compartment, an inexpensive Raspberry Pi computer board, powered by a motorcycle battery, recorded which buttons the raccoons pushed and switched the reward button as soon as they made nine out of 10 correct choices. A motor turned a disc with holes in it below a funnel to dispense the reward of dog kibble.
Many raccoons—and some skunks—were surprisingly eager to participate, which made getting clean data a challenge. “We had multiple raccoons just shove inside the device at the same time, like, three, four animals all trying to compete to get into it,” Stanton says. She also had to employ stronger adhesive to hold the buttons on after a few particularly enthusiastic raccoons ripped them off. (She had placed some kibble inside the transparent buttons to encourage the animals to push them.)
Surprisingly, the smart boxes revealed that the shyer, more docile raccoons were the best learners.
The jumping spider eye tracker
The thing about jumping spiders that intrigues behavioral ecologist Elizabeth Jakob is their demeanor. “They look so curious all the time,” she says. Unlike other arachnids, which spend most of their time motionless in their web, jumping spiders are out and about, hunting prey and courting mates. Jakob is interested in what goes on inside their sesame-seed-size brains. What matters to these tiny spiders?
BARRETT KLEIN
For clues, Jakob watches their eyes, particularly their two principal ones, which have high-acuity color vision at the center of their boomerang-shaped retinas. She uses a tool evolved from an ophthalmoscope that was specially modified to study the eyes of jumping spiders more than a half-century ago. Generations of scientists, including Jakob and her students at UMass Amherst, have built on this design, slowly morphing it into a mini movie theater that tracks the retinal tubes moving and twisting behind the spiders’ principal eyes as they watch.
A spider is tethered in front of the tracker while a video of, say, a cricket silhouette is projected through the tracker’s lenses into the spider’s eyes. A beam of infrared light is simultaneously reflected off the spider’s retinas, back through the lenses, and recorded by a camera. The recording of those reflections is then superimposed on the video, showing exactly what the spider was looking at. Jakob found that just about the only thing more interesting to a jumping spider than a potential cricket dinner is a black spot that is growing larger. Could it be an approaching predator? The spider’s lower-resolution secondary eyes catch a glimpse of the looming spot in the corner of the video screen and prompt the primary eyes to shift away from the cricket to get a better look.
