Caterpillar Of Land And Stream Discovered Reporting in the Proceedings of the National Academy of Sciences, entomologist Daniel Rubinoff describes 12 new species of caterpillar (Hyposmocoma). These Hawaiian moth larvae are the first insects shown to be able to live for weeks underwater or in bone-dry conditions.

Caterpillar Of Land And Stream Discovered

Caterpillar Of Land And Stream Discovered

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Reporting in the Proceedings of the National Academy of Sciences, entomologist Daniel Rubinoff describes 12 new species of caterpillar (Hyposmocoma). These Hawaiian moth larvae are the first insects shown to be able to live for weeks underwater or in bone-dry conditions.


Joining us now is Flora Lichtman, our video producer, soon-to-be video editor.

FLORA LICHTMAN: Hi, Ira. Thanks.

FLATOW: You're welcome. What have we got today for our Video Pick of the Week?

LICHTMAN: For the Video Pick this week, we have a - an organism with a very unusual adaptation. This is a caterpillar that can live underwater. Yeah, and you can see it living underwater on our Web site.

FLATOW: But they don't have to - I kind of - is it the same kind of caterpillar I see on my lawn or is it a different special kind of...

LICHTMAN: It is a special kind of caterpillar. And I think we should bring on one of the authors of the study, which is in PNAS this week. It's - Daniel Rubinoff is here with us. He's an entomologist at the University of Hawaii at Manoa.

Hi, Dr. Rubinoff.

Dr. DANIEL RUBINOFF (Entomologist, University of Hawaii at Manoa): Hi. How's it going?

FLATOW: Hey there.

LICHTMAN: So how did you discover that this caterpillar can live underwater?

Dr. RUBINOFF: Well, really, literally, I bumbled into it.

LICHTMAN: And where were you?

Dr. RUBINOFF: We were in the stream just above the UH campus, Manoa Stream. And we'd seen caterpillars of this type that I was working on crawling around the stream and near it. But in the process of collecting them, we literally bumbled into them crawling under the water, in the stream. And when you see a caterpillar...

LICHTMAN: Were you surprised?

Dr. RUBINOFF: Pardon?

LICHTMAN: Were you surprised to see them there?

Dr. RUBINOFF: A little bit. It seemed like a bad idea for any air-breathing insect.

(Soundbite of laughter)

Dr. RUBINOFF: But we realized that these caterpillars, they're about the length of your pinky nail. And when you're in a big stream that's about two feet deep, even though with a GPS, you're not going to get out of there for a couple of days because of the way they have to crawl. And that's what kind of got me thinking, maybe they aren't just holding their breath when the water gets high, but that they're actually able to go under the water, as well as stay above it. And that's actually what makes them truly remarkable.

LICHTMAN: Yeah, I was going to ask. I mean, what's the difference between this caterpillar and like a frog that can live on land or in water or, you know, a damselfly or certain nymphs?

Dr. RUBINOFF: In a word, it's commitment.

(Soundbite of laughter)

Dr. RUBINOFF: So - or the lack thereof. A damselfly as a nymph, has to be underwater. If you take it out of the water, it's going to literally suffocate like a fish and die. Conversely, a frog likes to take a dip. But if you put a frog in a tank and put a glass over it, most of them will die eventually. You know, some of them can last a little bit longer than others, but they need air, they have lungs. And these caterpillars have refused to commit one way or the other, or for some reason, been able to evolve a way to avoid being just underwater or just on land. And they're able to hang out on dry rocks, graze algae and lichen happily, and then as it happens frequently in Hawaii, we get heavy rain and the streams will rise several feet. And if you're a little caterpillar, you've got to hang on. You can't just swim to the surface when the water is raging like that.

And so these guys have figured out a way to literally breathe underwater. And, in fact, they're really nonplussed by it. They're the only animals I can think of that you can stick them in a dry rock and they're happy, or you can stick them in an aquarium with water and they're happy there too.

LICHTMAN: And you kept them for weeks in the lab, right, with...


LICHTMAN: ...with no place to come up for air or bask on the shore?

Dr. RUBINOFF: Absolutely, yeah. We call them the torture experiment. And we'd get a 10-gallon tank - and I did this several years ago because I really just couldn't believe it. And I put the caterpillars in the aquarium and left them there for a month. And they really just didn't seem to care.

LICHTMAN: A month.

Dr. RUBINOFF: And then my co-author, Patrick Schmitz, came over from Switzerland and was working with me, and he also didn't believe it. And I said, fine. You try it. And he did. And after a month, he had the same face I did, which is just these caterpillars simply don't care if they're underwater or out of it.

FLATOW: Well, but you said that they breathe underwater. How do you breathe -we have lungs. We breathe air. Fish have gills. Do they have gills?

Dr. RUBINOFF: Right.

FLATOW: So how do they breathe underwater?

Dr. RUBINOFF: Well, all insects - that's a great question. All insects have a, sort of a different way of breathing than the lung and gill thing that vertebrates use. They have spiracles all along the sides of their body. So if you wanted to suffocate an insect, you couldn't put your hand over its mouth. It wouldn't work, because it's literally breathing through holes that are regularly spaced along the entire body.

And it has what you would call, I guess, a direct respiration system, which is trachea and little tracheoles, which in humans would be something like capillaries and blood vessels, that get smaller and smaller, and literally put almost every cell or every other cell in the insect's body in contact with the atmosphere to exchange gas. So that's the game plan when you're above water. When you're below water, insects will develop gills that increase their service area for gas exchange or specialized other structures that help them mediate that gas exchange between the water and their bodies and their metabolic needs.

The crazy thing about these caterpillars is we - I can't tell you exactly what they do. I can tell you what they don't do, because we keep looking for evidence of gills. And with high tech scanning microscopy, we haven't found them. We've looked for modifications that would suggest something that they were doing and we haven't found it. And so I've come to, sort of, the last gasp, which is they're probably breathing directly through their skin.


FLATOW: That's what Sherlock Holmes would say, wouldn't he?

(Soundbite of laughter)

FLATOW: When you've given up all the, you know, when you've eliminated all the logical situation, things that don't make sense was the truth.

Dr. RUBINOFF: Right. Right.


Dr. RUBINOFF: And there is some precedence for gas exchange through the skin in other animals, but to be wholly dependent on that, that's kind of a different story. We do have a little bit of evidence for that, which is maybe anecdotal. And that is the first time I collected these caterpillars in the water, I put them in a tub with a little rock on it in my apartment and I went out for the afternoon. And the next day, I noticed a horrible smell and all the caterpillars had died. And I realized that this was a tub of still water. And what it turns out is, is that these caterpillars need water with very high level of dissolved oxygen. So it simply had...

LICHTMAN: Like a bubbler for your fish tank.

Dr. RUBINOFF: Yeah, a bubbler, exactly. If you're going to keep them in captivity, it's a bubbler. Out in the world, it's a mountain stream, something like where you'd find trout. So they're aquatic in the same way that trout are. And that is that they need high oxygen concentrations in the water to do what they're going to do.

FLATOW: And, in fact, in the film that Flora has made in our SCIENCE FRIDAY Video Pick of the Week, you do show - you show us on our Web site, at, you do see a raging little brook there, right?

Dr. RUBINOFF: Right. Right.

FLATOW: And these tiny little caterpillars are just crawling along in the water.

LICHTMAN: Yeah. And I think we should talk about how they look, because they have this sort of - they just have this sort of unusual thing.

Dr. RUBINOFF: They're cute.

LICHTMAN: They're very cute. Yes.

(Soundbite of laughter)

FLATOW: They look like they're dragging some baggage along with them.

LICHTMAN: Yeah. What are they wearing?

Dr. RUBINOFF: Aren't we all?

(Soundbite of laughter)

FLATOW: We'll talk about that later.


FLATOW: But I mean, let's talk - caterpillar-wise, they have - so you - in the film, I could see there's like silk, some sort of little silky things.


LICHTMAN: And these shells, right?

Dr. RUBINOFF: Exactly. Absolutely. And maybe the best way to think about it is something like a hermit crab. These caterpillars spin a silk case that they hide out in. And they just peak out their head and their first six legs and crawl along with those while using the abdomen to hold the case in place. So, yeah, they're quite conveniently packaged to cruise around underwater.

But I don't think that that case is the secret to their success because the 12 species that we've identified in that paper are part of a much bigger group with probably well over 400 species, most of which overwhelmingly are terrestrial. So they all carry cases, these guys are diving with the cases but other ones can't do that.

FLATOW: Well, we're talking about caterpillars that live underwater on SCIENCE FRIDAY from NPR. I'm Ira Flatow here with Flora Lichtman and Dr. Daniel Rubinoff. So they don't all have the cases, then?

Dr. RUBINOFF: Oh, no. They all do.

FLATOW: They all have the cases but...

Dr. RUBINOFF: That's their trademark.

FLATOW: That's it.

LICHTMAN: But only special cased ones can go underwater, right?

Dr. RUBINOFF: Yeah. And this is where it gets even a little bit muddier. We can't say that there's a specific case type that you have to have to go diving. There's cone cases that are diving underwater, there's burrito cases that are diving underwater and there are bugle cases diving underwater. But all of them also have sister species, that is cone cases, bugle cases and burrito cases that don't dive, that can't go underwater. So it has to be something more than just the case that they have that lets them go underwater.

LICHTMAN: You have to be a special burrito, as you said, to...

Dr. RUBINOFF: Exactly. A special burrito. You have to - or a special cone or a special bugle (unintelligible).

FLATOW: But you don't know what that specialty is yet.

Dr. RUBINOFF: Exactly. And that's the mystery that keeps on going. I think we're going to put that in the sequel.

(Soundbite of laughter)

LICHTMAN: You know, one thing that seems interesting is there are not other organisms that are known to do this, right? Why do they exist here? What's -what evolutionary pressure drove this adaptation?

Dr. RUBINOFF: Now, that's a $20 million question.

(Soundbite of laughter)

FLATOW: We don't have the money. So give us a 10-cent answer.

(Soundbite of laughter)

Dr. RUBINOFF: I don't have the answer so we're all right. I think what it is is probably a special combination of an isolated island chain like the Hawaiian islands and then having the right template that is the ancestor of these moths, these hyposmocoma that arrived maybe 20 million years ago and was able to explore different ecological opportunities. This group that includes these aquatic caterpillars also has a bunch of other wacky species in it that are also hyposmocoma, one of them attacks and eats snails. And so there's a bunch of species that do that that are all related. But Hawaii is the only place so far on the planet that has a caterpillar that attacks snails. There's another one that bores into rotting wood and eats rotting wood. So these guys have really become - each species has developed into a different, sort of, niche, if you will, and they've become a jack-of-all-trades.

LICHTMAN: Hmm. Full of oddity adaptations in this, you know...

FLATOW: So they've adapted where they've had to, how they've had to, in the place that they've been in.

Dr. RUBINOFF: Exactly.


Dr. RUBINOFF: Exactly. And it's been really exciting to see just how much diversity there is in this group.

FLATOW: So you're going to hunt around for more of these guys?

Dr. RUBINOFF: Oh, absolutely. You know, we've actually got more than 89 species that we've worked with so far. And there just seems to be no sign that they're going to let down in terms of diversity. The number of different case types that they spin is just tremendous. And we've actually run out of names for them. We've got...

LICHTMAN: Yeah. Give us some of the names because they're so...

FLATOW: You got your own name in any of them?

(Soundbite of laughter)

Dr. RUBINOFF: Well, no. That wouldn't be nice. But things like oyster shell or candy wrapper or mini burritos.

FLATOW: Those are the actual names of the species?

Dr. RUBINOFF: These are the names of the case types.


Dr. RUBINOFF: So the candy wrapper case type has perhaps 12 species that occur across all the main Hawaiian islands. The dog bones occur on most of the islands as well. The oyster shells we're having trouble finding on the big island but we see them on the Lana'i and Maui for example. So...

FLATOW: Mmm. And you can see this in Flora Lichtman's Video Pick of the Week. And you can see the bugles are named not after the musical instrument.

Dr. RUBINOFF: Snack food.

FLATOW: The snacks.

(Soundbite of laughter)

Dr. RUBINOFF: If you do field work, food is on your mind.

(Soundbite of laughter)

FLATOW: So we could see Doritos and Cheetos somewhere along the line, maybe.

Dr. RUBINOFF: I would never say it's impossible. In fact, I'm wondering what the next flavor, I mean, case will be.

(Soundbite of laughter)

FLATOW: All right.

LICHTMAN: Thanks, Dr. Rubinoff.

Dr. RUBINOFF: It's been my pleasure. Thank you for having me.

LICHTMAN: Daniel Rubinoff is an entomologist at the University of Hawaii, Manoa.

FLATOW: And thank you, Flora.

LICHTMAN: Thanks, Ira.

FLATOW: Flora Lichtman is our producer of our Video Pick of the Week. And this is really something you've never seen before, I think. Go to our Web site at and see these caterpillars that live underwater. And they're crawling around and have little cases on them. See what shape you would call them.

Thanks, Flora. We'll see you next week.

LICHTMAN: See you next week.

FLATOW: And we'll see you all next week.

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