Little is known about the night-time habits of tiny creatures all around us. Take the jumping spider--it mysteriously can spend much of the night suspended in mid-air, hanging by a thread.

Transcript

MARY LOUISE KELLY, HOST:

One of the most common spiders you might see around your home is a jumping spider. They don't make webs. Instead, jumping spiders have four pairs of big eyes that help them spot prey and pounce. NPR's Nell Greenfieldboyce reports scientists recently realized that at night, in the dark, these spiders do something unexpected.

NELL GREENFIELDBOYCE, BYLINE: Daniela Roessler had been doing experiments with jumping spiders at Harvard University. She wanted to understand whether and how jumping spiders recognize predators that might try to eat them. But then the pandemic hit, so she went home to Germany. And there, in a dry, grassy field, she went out and collected a different species of jumping spider.

DANIELA ROESSLER: They have really cute, stripy faces. I think in English they're actually called gorilla jumping spider because the males have these huge, big, black forearms, which makes them look a little bit funny.

GREENFIELDBOYCE: The spiders were in plastic containers on her windowsill. One night, she came home after being out for dinner.

ROESSLER: And I switched on the light. And I looked on the windowsill and was like, oh, God, what happened to these animals? Are they dead?

GREENFIELDBOYCE: The spiders were hanging from the ceilings of their plastic boxes - just hanging by a single thread, suspended in midair, motionless. Roessler thought, what is this? It was very different than the little silken retreats that jumping spiders are known to build for resting in, say, rolled-up leaves. She went back out to the spot where she collected these spiders, this time at night.

ROESSLER: We found a lot of them. So basically, we found three times the number of individuals during the nights compared to what we found during the day because it's just so easy to spot them when they hang from the vegetation like this.

GREENFIELDBOYCE: It turns out the spiders spend hours at night hanging upside down. And if she gently touched the silk thread, almost all spiders would immediately drop to the ground.

ROESSLER: Maybe they use their silk as a - kind of an alarm system or as a way of, like, getting out of reach for predators.

GREENFIELDBOYCE: Like ants or other spiders - still, the spiders she had in boxes would sometimes make a little silk retreat for themselves.

ROESSLER: And that meant that they were switching between different resting strategies. Something informs them about how to make this choice, where to spend the night, how to spend the night.

GREENFIELDBOYCE: She's still trying to figure out what's going on but says this just goes to show that science knows very little about the nighttime resting habits of very tiny critters, even common ones. Amita Sehgal studies sleep at the University of Pennsylvania.

AMITA SEHGAL: What I thought was really interesting was that they were talking about this suspension as being something that helps them avoid predation. We kind of talk about sleep as something that makes them more susceptible.

GREENFIELDBOYCE: Because a sleeping animal isn't alert to danger - the sleep field has long focused on mammals and birds. The few invertebrates that are studied, like the fruit fly or worms, generally get examined in the lab, not out in the wild where predators lurk.

Nell Greenfieldboyce, NPR News.

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