[MUSIC PLAYING] JAY STAFSTROM: What's not unusual about these spiders? They have the biggest size eyes of any spider. They're 2,000 times more sensitive to light than humans are. The way that they hunt is fascinating. They're called netcasting spiders because they actually-- they make this little rectangular net, and they dangle above the ground or a leaf, and they'll throw it down or actually hit things out of the air, which is-- it's incredible to see.
They can-- yeah, they really like to eat mosquitoes, which is fabulous. I can find them pretty easily in Florida. I typically go to parks around Gainesville, and you can get good numbers there. I've also found them at a rest area outside of Savannah, Georgia. So they're at least in two states, but probably not many more.
So during the day, they're very cryptic, and they look like little sticks. But I think they've evolved, potentially, to look like the end of palm fronds. So really whenever I'm looking for the, I look for palms first. And so any state that doesn't have palm fronds might not find them.
So the infrared video was part of this field study that I did out in Florida, Gainesville, Florida. And I went out, and I was trying to test whether or not these spiders actually use vision for foraging. For decades, it's been assumed that they had these really big eyes, and they hunt in this really seemingly visually demanding manner. So they have to use these big eyes for hunting.
So I went out, and I tested that. So I went, I grabbed a bunch of spiders, and I temporarily blinded them with dental plastic. And what's really nice is that after you put it on the eyes, you can actually remove it afterwards. So for every spider that I caught, I could blind them, put them back where I found them, let them make their web, and see how well they could still hunt with or without vision.
I found that when spiders were blinded, when they couldn't see out of their big eyes, they were significantly worse at foraging. And the most interesting part is that it's really what they couldn't catch was most interesting to me because they couldn't catch things off the ground when they couldn't see, but they could still catch things out of the air.
It suggests that they've evolved these large eyes to catch things off the ground primarily. It also suggests that they can catch still a good number of prey without these enlarged eyes, which is also pretty neat. And as far as web-building spiders go, not many of them can catch things both off the ground and out of the air. So they're definitely in a good niche.
I'm here visiting the Hoy Lab, and I'm working with Ron Hoy and Gil Menda. And their team have figured out a way to get live recordings of spiders and neural activity. And so right now, we're plugging electrodes in these spiders and playing back a bunch of different stimuli and seeing how they react and, yeah, different sensitivity thresholds and contrasts.
We've had some really exciting recordings pretty much from the first day. We figured out that they're very sensitive to auditory stimuli and at really high frequencies, which no one really expected.
GIL MENDA: We've got a very nice single unit. You can see here the very, very nice single unit. And what we found when we record from the brain that they are very sensitive at the low frequencies, and also they went up to high frequencies. But when I recorded from the leg of the netcasting spider, we found they are very sensitive all the way up to almost 5 kilohertz. And in the low frequency, we couldn't see much responses from the leg from the sensor.
RON HOY: I have found sensitivities out to 5 kilohertz. Now, from the behavior of the animal itself, we wouldn't have suspected that. So what I really like about your findings is that by using electrophysiological measurements, we open up a window into the spider's sensitivity that have not or have not heretofore been demonstrated through either behavior or morphology.
JAY STAFSTROM: So they can catch things out of the air, so you think that they'd be sensitive to 100-200 hertz, but they're sensitive to 5 kilohertz sound, which is-- it's a mystery. We don't know what exactly-- like, what the function of that is. And we also don't know how they do it. We don't know the organ that they're using to actually pick up these frequencies.
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Net-casting spiders spin small webs which they hold with their four front legs. They plop these webs down on insects crawling nearby and also use them to catch flying insects. These spiders have enormous eyes that are about 2000 times more sensitive to light than ours. Jay Stafstrom, a researcher at the University of Nebraska, has found that blinded net-casting spiders cannot catch crawling prey, but are still perfectly capable of snaring flying insects. In Ron Hoy's lab at Cornell, Gil Menda has recorded from the spider's brain and found that they, like mosquitoes, are sensitive to low frequency sounds, but they are also sensitive to high frequencies, near 5,000 Hz. The function of this high frequency hearing is still a mystery.