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MARY LOUISE KELLY, host:

And now we go from creatures in the water to creatures in the sky. Here's what we'd like you to do this morning: look up at the sky and ask yourself, who's up there? Maybe you'll see a bird or a cloud or two, but according to researchers, that empty-looking space is teeming with wild animals. Well, they're very little wild animals, but still, NPR's science correspondent Robert Krulwich wanted to know more.

ROBERT KRULWICH: How did you even happen onto this question? Are you a guy who looks up a lot? Or...

(Soundbite of laughter)

Dr. MATT GREENSTONE (Entomologist): Yes.

KRULWICH: Matt Greenstone studies bugs. He's a research entomologist in Maryland, and years ago, he says...

Dr. GREENSTONE: On a balmy fall afternoon, I was biking home when suddenly, little black specks started falling out of the sky.

KRULWICH: Down they came, little black dots, looking kind of like strange black rain.

Dr. GREENSTONE: And there must have been - I'm sure there were millions of them.

KRULWICH: And as they landed, he thought, now, wait a second: these things, they're alive. Because if you look really closely at them...

Dr. GREENSTONE: You could see that they had legs.

KRULWICH: Eight legs.

Dr. GREENSTONE: These were spiders.

KRULWICH: Spiders.

Dr. GREENSTONE: So, they had just fallen out of the sky.

KRULWICH: And if this freaks you out, hold on, hold on, 'cause we're going to ask a very interesting question here. Matt figured...

Dr. GREENSTONE: What comes down must have gone up. And how in the world did they get up there?

KRULWICH: Whoever heard of flying spiders? Well, says entomologist May Berenbaum, 90 years ago, people already knew there were all kinds of bugs high off the ground.

Dr. MAY BERENBAUM (Entomologist): Particularly when early planes would come back with, like, aphids plastered all over them. You know...

KRULWICH: Aphids?

Dr. BERENBAUM: Oh, yeah.

KRULWICH: And are aphids and spiders up in the air by mistake?

Dr. BERENBAUM: Nope.

KRULWICH: May says these animals want to be carried off, and you can see them -moths and gnats and wasps - deliberately launching themselves into the air, especially the turbulent level of air, just up off the ground.

Dr. BERENBAUM: They'll climb up to a high point in their own environment, even if it's just a blade of grass.

Dr. GREENSTONE: They just stand straight up on their little back legs, and just by doing that, they can get part of their body up into this layer where it's more turbulent. And then, if you can get a ride on a parcel that's going up, you can get off the ground. And then if you're lucky...

(Soundbite of music)

Dr. GREENSTONE: ...you can get carried aloft.

KRULWICH: Sometimes you can see them actually leaping. But, says Matt...

Dr. GREENSTONE: The way a spider does it is it has a silken thread which can be quite a few numbers of meters long.

KRULWICH: And what the spiders who landed on Matt and his bicycle did back those many years ago, is he watched them crawl to the highest point they could.

Dr. GREENSTONE: Whether was my finger or the bell on the bicycle, stick their little butts up in the air, which is where the silk comes from, and if the silk was caught by the breeze, they'd depart again.

KRULWICH: Insects sometimes need to leave where they are and go someplace else, either for food or sex or for a variety of reasons, bugs and spiders disperse. And when they do...

Dr. BERENBAUM: They're kind of gambling that wherever they end up is going to be better than where they're just leaving from.

KRULWICH: So when you go out this month and you look up at a clear blue sky and you see nothing up there but air and blue and clouds, it turns out you are standing under a vast, teaming highway of animals invisible to you. But according to bug specialist Hugh Raffles and May Berenbaum and Matt Greenstone...

Dr. GREENSTONE: There's all manner of stuff are floating around up there.

Prof. HUGH RAFFLES (Bug Specialist): They found lady bugs at 6,000 feet.

Dr. GREENSTONE: Really tiny mites which don't even have wings.

Dr. BERENBAUM: Parasitic flies, tiny little wasps.

Prof. RAFFLES: Cucumber beetles at 3,000 feet.

Dr. BERENBAUM: Aphids.

Dr. GREENSTONE: Lots of aphids.

Prof. RAFFLES: Scorpion flies at 5,000 feet.

Dr. BERENBAUM: Thrips.

Dr. GREENSTONE: Micro wasps.

Prof. RAFFLES: Little fruit flies at 3,000 feet.

Dr. GREENSTONE: And scale insects.

Dr. BERENBAUM: Yup. There's a lot of insects.

Prof. RAFFLES: Yeah. They're all up there.

(Soundbite of music)

KRULWICH: When scientists first calculated the number of bugs in the sky on a typical, oh, I don't know, summer month...

Dr. BERENBAUM: The numbers were staggering.

KRULWICH: To count bugs, what scientists do is that they imagine, let's say, a column of air one mile across going way up into the sky. And then they'll measure how many insects pass through that column in a month. The most recent answer - and this was done with a radar device in Great Britain, by a team headed by Jason Chapman, and we found Jason.

Dr. JASON CHAPMAN (Entomologist): We estimated about 30 million large insects had passed through in a month.

KRULWICH: Did you say 30 million?

Dr. CHAPMAN: Thirty million.

KRULWICH: And these are the large guys.

Dr. CHAPMAN: These are the large ones. Our estimate for all of the insects, including all of the aphids and the tiny creatures, was three billion - so, 3,000 million.

KRULWICH: Three billion.

Dr. CHAPMAN: Yeah.

KRULWICH: That's like 10 times the population of the United States going over your head.

Dr. CHAPMAN: Yeah.

KRULWICH: That's enormous.

Dr. CHAPMAN: It is enormous. Yes.

Dr. BERENBAUM: And the entomologists were all absolutely amazed at what they fished out of the sky.

(Soundbite of laughter)

Dr. CHAPMAN: I was surprised. No doubt about that.

KRULWICH: Because there's so much going on right over our heads that we didn't know anything about.

Dr. BERENBAUM: It's just that we have this notion that we own the planet, and that's kind of not the case.

KRULWICH: But we do have our own animation, so you can watch a spider sailing high off the Earth, dangling on a tiny silk thread. You can see the all-time altitude champion, a single male termite soaring 19,000 feet up, followed by a plummet to a sea of beetles and aphids and butterflies in glorious detail at

And I am Robert Krulwich, at NPR News.

(Soundbite of music)

KELLY: You're listening to MORNING EDITION, from NPR News.

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