Despite inhabiting sewers and cesspools, cockroaches are quite clean — or at least their exteriors are, according to entomologist Coby Schal of North Carolina State University. That's because cockroaches are constantly grooming themselves, particularly their antennae. Publishing in PNAS, Schal and colleagues investigate why they groom.
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IRA FLATOW, HOST:
Time now for our Video Pick of the Week. Flora Lichtman is here. Welcome to the program. Flora's our correspondent and managing editor for video.
FLORA LICHTMAN, BYLINE: Hi, Ira.
FLATOW: This one, this week...
LICHTMAN: I don't even know what to say.
FLATOW: Have you - make sure you've eaten your lunch or your breakfast.
LICHTMAN: It might be - it's going to be the grossest video you've probably seen all week. But you should still watch it because it's fascinating.
FLATOW: You know how to sell it.
LICHTMAN: Yeah, I'm sorry. OK. Is it...
FLATOW: Gross sells, yeah.
LICHTMAN: The video is about the bathing habits of cockroaches. It's something you maybe didn't know you were interested in. But believe me, it really is amazing. So here's the first "aha" of this video and there are so many, thanks to entomologist Coby Schal, who studies them. So first of all, he told me that cockroaches are actually, in one way, at least, really clean. They're fastidious groomers. They spend a lot of time during the day grooming themselves. And they usually do it in this stereotyped manner where they start with their antennae and they take one opposing - the opposing hand, pull down the antennae on the other side and then run it through their mandibles like dental floss.
FLATOW: Just picture that. Well, you don't have to picture it. It's up on our website.
LICHTMAN: You don't - you can see it...
FLATOW: You can see it up on our website...
LICHTMAN: ...in HD glory.
FLATOW: ...up there at sciencefriday.com on our webpage. You can also take it along with you on your iPad or iPhone or Android. But they run - this is an amazing photo. It's - because this thing is huge. It's very long. The antenna is very, very long.
LICHTMAN: It is very long. And they run it from base to tip through their mouth. And they do this all the time. And Coby Schal wondered, why are they spending all this time grooming? What are they actually grooming off? And he said there have been a lot of hypotheses about this, but no one had actually tested it. So they did a couple of things that are - it's so funny. So first of all, to test why a cockroach grooms, you have to prevent the cockroach from grooming, which presents an interesting challenge: How do you get the cockroach to cooperate with you?
And they came up with something sort of like one of those dog cones that prevents dogs from scratching. But it's a teeny, tiny antenna cone made from the tip of a pipette that they put on the base of the antenna. So the cockroach can't actually pull it down. So on a cockroach now, they have one antenna that's being groomed and they have this other antenna that the cockroach can't groom anymore. So they can see what happens to the dirty antenna, and they find that all of this gunk starts to accumulate on the antenna.
And the gunk is actually these cuticular hydrocarbons. And they're sort of like a wax that the cockroach secretes to prevent itself from drying out. So that's good. But too much of it and it clogs the pores that are on the hairs that are on the antenna. And this actually is bad because they use these pores to smell.
FLATOW: They have to smell.
LICHTMAN: So complicated but amazing.
FLATOW: Yeah. Well, you don't want to get cockroach acne if you clog the pores. But that's something else.
LICHTMAN: Yes, this is not just a hygiene thing.
FLATOW: This is not. So - that - and you can see this on our website at sciencefriday.com.
LICHTMAN: You can see this in glorious detail - glorious gross detail.
FLATOW: But there is one ending of this story.
LICHTMAN: Right. So I was like, this is amazing - cockroaches have been unfairly maligned for all this time. But Coby Schal assured me that there's more to this story.
DR. COBY SCHAL: The other thing that comes into play here is that everything that a cockroach grooms off of its body, it ingests. So if the cockroach is in a sewer system and it's bathing in this cesspool of microbes that are pathogenic to humans, the cockroach then grooms itself, ingests these pathogenic microbes. And then if it makes its way into the kitchen, it can defecate those microbes onto our steak or spaghetti.
FLATOW: I told you eat to lunch first.
LICHTMAN: There you have it.
LICHTMAN: So there you have it. It's not exactly, you know, it maybe - keep itself tidy. But there...
FLATOW: The truth sometimes is hard to digest, so to speak.
LICHTMAN: Ooh. Good one.
FLATOW: Well - and there - if you want to see the whole - it's a great video. If you want to see cockroaches grooming and what happens after they finish their grooming, it's up there on our website at sciencefriday.com. It'll be up there on YouTube also. And how they figured - it's a great video, Flora.
LICHTMAN: And, you know, you could probably observe this, if you live in New York, in your own home.
FLATOW: Too many times.
FLATOW: Thanks a lot, Flora.
LICHTMAN: Bye. Transcript provided by NPR, Copyright NPR.