What do jumping spiders consider sexy? How DIY technology offers insight into animal minds.

The raccoon smart box

Why are raccoons so good at living in the city? One theory is that it’s because they’re flexible thinkers. To test this idea, UC Berkeley cognitive ecologist Lauren Stanton adapted a classic lab experiment, called a reversal learning task. For this test, an animal is rewarded for learning to consistently choose one of two options, but then the correct response is reversed so that the other option carries the reward. Flexible thinkers are better at reacting to reversals. “They’ll be better able to change their choices, and over time, they should be faster,” says Stanton.

To test the learning abilities of wild urban raccoons in Laramie, Wyoming, Stanton and his team built a set of “smart boxes” to deploy on the outskirts of the city, each with an antenna to identify raccoons that had been previously captured and microchipped. Inside the box, the raccoons found two large buttons—coming 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 pressed and switched the reward button as soon as they made nine of the 10 correct choices. A motor rotated a disc with holes under a funnel to dispense the dog’s kibble reward.

Lots of raccoons—and some skunks—they were surprisingly eager to participate, which made getting clean data a challenge. “We’ve had several raccoons get into the device at the same time, like three, four animals trying to compete to get in,” Stanton says. He also had to use stronger adhesive to hold the buttons down after a few particularly enthusiastic raccoons ripped them off. (I had placed a kibble inside the clear buttons to encourage the animals to push them.)

Surprisingly, the smart boxes revealed that the shyest and most docile raccoons were the best learners.

The jumping spider eye tracker

The thing about jumping spiders that intrigues behavioral ecologist Elizabeth Jakob is their behavior. “They seem 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-sized brains. What do these little spiders care about?

BARRETT KLEIN

For clues, Jakob looks at their eyes, especially the two main ones, which have high-acuity color vision in the center of their boomerang-shaped retinas. He uses a tool evolved from an ophthalmoscope that was specially modified to study the eyes of jumping spiders more than half a century ago. Generations of scientists, including Jakob and his students at UMass Amherst, have built on this design, slowly transforming it into a mini movie theater that follows retinal tubes that move and twist behind the main eyes of the spiders while watching.

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 retina, returned through the lenses, and recorded by a camera. The recording of these reflections is then overlaid on the video, showing exactly what the spider was looking at. Jakob discovered that almost the only thing more interesting to a jumping spider than a potential cricket dinner is a black dot that is getting bigger. Could it be an approaching predator? The spider’s low-resolution secondary eyes zoom in on the dot approaching the corner of the video screen and cause the primary eyes to move away from the cricket for a better view.