Are you mosquito bait?


Full Transcript

Announcer: Welcome to Stuff from the Science Lab from howstuffworks.com.

Allison Loudermilk: Hey, guys, and welcome to the podcast. This is Allison Loudermilk, the science editor at howstuffworks.com.

Robert Lamb: And this is Robert Lamb, science writer at howstuffworks.com. And we are podcasting to you from the Georgia summer, which means heat and mosquitoes.

Allison Loudermilk: Yes, lots of mosquitoes. So let's talk about the obvious question out there, do mosquitoes flock toward you?

Robert Lamb: Anytime I'm at an outdoor event and someone gets bitten by a mosquito, that's the instant conversation topic. Someone's always like, "I'm mosquito bait." Or they'll be like, "Normally, I get bitten by mosquitoes and my husband doesn't." Or it's vice versa. It's something we all have some experience with, but I don't think any of us have necessarily figured it out.

Allison Loudermilk: So I had my in-laws staying with us a few weeks ago, and my mother-in-law happens to be one of the people who says mosquitoes flock to. And she gets a lot of bites. And no kidding, she went up to this loft spare room area that we have a whole bunch of our stuff in and also our lovely guests get to stay in -

Robert Lamb: And you keep it stocked with mosquitoes?

Allison Loudermilk: No. That's the point. Nobody's ever up there. There's a fan going, so maybe the fan would deflect mosquitoes. But she went up there, and within minutes she was bitten five times. I felt bad. I felt terrible. I felt like she thought we lived in some mosquito ridden hovel. But I think they really do like her.

Robert Lamb: And that comes to the interesting question, do mosquitoes really like some people more than others or is this just BBQ hearsay.

Allison Loudermilk: Well, you can count on science to get to the bottom of some of these mysteries. So we did a little digging and as it turns out they really do exhibit a preference for certain folks. So back in 2001, a guy by the name of David W. Kelley published a paper in Trends in Parasitology. And it was called, appropriately enough, Why Are Some People Bitten More than Others.

Robert Lamb: These scientists and their titles, I swear.

Allison Loudermilk: I thought that was a pretty good one. In this case, Kelley says humans will get bitten by bloodsucking insects infrequently. All of us are going to get a bite, right? Nobody's immune to it. But a special subset of that population will be "heavily attacked." So let's quantify the numbers that Kelley starts throwing around in his paper. So put 10 people in a room with some anopheles mosquitoes - and those are the notorious specters for the malarial parasite, plasmodium - and two of those people in that room are going to be responsible for passing on 80 percent of the disease. So let's talk about that again.

Two people are going to pass on 80 percent of the disease, according to Woolhouse et al. So that's pretty crazy. And that does seem to point toward the idea that in fact mosquitoes do exhibit a preference. From a public health perspective, imagine if you could really home in on that 20 percent and find out what makes them so attractive. Not only would companies interested in mosquito control be hugely interested in this -

Robert Lamb: But the rest of us would want to hang out with them more. There's mosquitoes everywhere, call up Charlie. I want him standing next to me.

Allison Loudermilk: Right. Mosquito bites are annoying and we're kidding about it, but if you think about all those people who died from malaria or other mosquito-born diseases, it really stinks.

Robert Lamb: Well, this is interesting. This is a slight tangent here, but I ran across a really cool argument for mosquitoes. Because mosquitoes are one of things that you frequently heard, "Why do we have mosquitoes? If there's a god in heaven, why did he create mosquitoes?" But one interesting argument for them is that mosquitoes and their malaria have kept humans out of certain areas of the world for long periods of time, or at least kept them from expanding into those areas in large numbers. So the argument is that if you're an environmentalist or a tree hugger, then you have to thank mosquitoes for protecting these areas up until modern times.

Allison Loudermilk: That's definitely an interesting perspective. I definitely wouldn't advocate getting rid of mosquitoes, nor could we ever reasonably hope to do it. But I do advocate effective public health interventions.

Robert Lamb: Yes, definitely. Especially when we're creating situations through overpopulation or poor water storage management that encourages massive quantities of mosquitoes.

Allison Loudermilk: So let's talk about some of the likes and dislikes. What's going on here? Who are the people getting all the bites?

Robert Lamb: Well, it's like you're walking down the street trying to figure out which restaurant you're going to hit. There are different cues that are going to stand out to you and may help you make up your mind about where you're going to eat. And it's similar to mosquitoes. The big one, of course, is CO2, which we're constantly exhaling. And bigger people give off more CO2.

Allison Loudermilk: Right. This is not rocket science, so you guys know this.

Robert Lamb: So they're going to be drawn to the larger people, and a lot of times that generally breaks down to men as well.

Allison Loudermilk: Right. So they'll show a preference for an adult over a child or a man over a woman. I was reading an article about this that Anahad O'Connor had posted in the New York Times, and he was saying that it had been posited that women were sweeter because of estrogen and thus mosquitoes favored them more. But the bigger size and all of that heat and CO2 are what really get mosquitoes excited and biting.

Robert Lamb: Yeah, they also think that pregnant ladies attract them more. But it comes down to the CO2 again, heavier breathier.

Allison Loudermilk: Right. And doubtless we're going to get a couple of small listeners out there who swear they are the ones who attract all the mosquitoes, so size isn't the be all and end all, nor is CO2. A couple of other things do factor into it. And nobody knows the exact formula for attracting that mosquito, but we do know a couple of the factors. So CO2 is one of them.

Robert Lamb: And again, with CO2, if you're an active little person and you're out there jumping around, playing volleyball, shooting hoops -

Allison Loudermilk: Yeah, you're all active because nobody's going to notice you because you're a small person.

Robert Lamb: Yeah, talking with your hands, etcetera, then you're producing more CO2 and you're likely to attract - it's amazing how far away they can sense you. They can smell a meal 165 feet away. I'm not sure I could smell a meal 165 feet away, unless it was BBQ off a truck and I was downwind of it, maybe.

Allison Loudermilk: Right. When you think about it, they can cover up to a mile or a mile and a half in an hour; they can cover some serious ground to get to you if they want. So let's talk about smell. Are you wearing perfume? I assume you're not. I read one -

Robert Lamb: You make it sound like I stink in here or something.

Allison Loudermilk: No, no. I'm not saying that you stink. But I did read a comment to an article where this woman was swearing that mosquitoes love Shalimar.

Robert Lamb: What's Shalimar?

Allison Loudermilk: It's a ladies' perfume. It's kind of old school. So if you are wearing perfume, this could attract it. And then less good smelling things attract mosquitoes. But what's the perfect stinky combo?

Robert Lamb: It's sounding like, from what we've covered so far, if you were a large out of breath person -

Allison Loudermilk: Who moved your hands?

Robert Lamb: - who moves her hands, then you're probably pretty attractive.

Allison Loudermilk: Wearing Shalimar.

Robert Lamb: Yeah. And if you really want to tip the scales, start drinking a bunch of beer. There are a lot of weird myths out there. I was actually at a thing last night where there were a lot of mosquitoes around. And I was asking people, "We're doing this podcast tomorrow. What have you heard actually attracts mosquitoes?" I heard if you eat bananas it will attract mosquitoes.

Allison Loudermilk: Garlic floats around there. The Vitamin B-12.

Robert Lamb: Yeah.

Allison Loudermilk: I was researching some of these because you brought these to my attention. And I went on the American Mosquito Control Association Site - so bear in mind the source, they're bound to have some industry interest. But they said that garlic, Vitamin B-12, and all of those other systemic don't in fact prevent the mosquitoes from biting. And the bananas don't necessarily attract them, either. My favorite fact from this particular website, they mention that limburger cheese has also been found to be attractive to mosquitoes. And they took it one step further. They said that perhaps that attraction to limburger cheese was because it resembled the smell of human feet.

Robert Lamb: Okay. So big person, out of breath, talking with your hands, drinking beer, and then maybe eating limburger cheese - or just having stinky feet!

Allison Loudermilk: Also, not sitting under a fan. Because if you're hanging out under a fan, then -

Robert Lamb: That's going to disperse the CO2. You're going to be sitting in this big bubble of CO2 funk. And often they say to have a fan going because it keeps them away from the meal area if you're having picnic or whatever. So I guess it works in that regard, too. It stirs up the CO2 and keeps it from settling and being a big bat signal for mosquitoes.

Allison Loudermilk: So let's get into an experiment that checked out one of these factors. It was alcohol, in fact, according to a paper published in PLoS One back in March 2010. It had a most excellent title. It said, Beer Consumption Increases Human Attractiveness to Malaria Mosquitoes. So you can look up the paper if you want, if you're so inclined.

Robert Lamb: Quite a straightforward title.

Allison Loudermilk: It reminds me of something that might be in the Improbably Research Journal. But, no. It was not improbable - in fact it was probable and it was carried out in Burkina Faso, an area of Africa that sees a fair amount of malaria. So let's check out what happened with this experiment. Like most of you guys listening, researchers noticed that malaria and alcohol consumption represents some pretty big public health problems. So they decided to investigate the links between the two. It seems like a good idea, right?

Robert Lamb: Right.

Allison Loudermilk: So here's what they did, and it didn't involve getting a bunch of participants drunk and letting them hang out with a bunch of bloodthirsty mosquitoes.

Robert Lamb: That's what I thought it was going to be. Kind of like some of these other experiments we've encountered where a scientist will invite some people over and they think it's a cocktail party, but it's really a psychological experiment.

Allison Loudermilk: No. There's a whole section in the paper devoted to ethics, so these researchers took the ethical steps. So what they did was take 43 adult males between ages 20 and 43 - and they're from, of course, Burkina Faso - to participate in their study. So they randomly assigned their beer drinking participants to - this is the big disappointment for some who signed up - the beer group or the water group. You have to have a control group. And the beer in question was a local beer called Dolo. It's pretty low at three percent alcohol content and it's the most popular drink in the region.

So it makes sense to test it out with the most popular drink in the region. And not just the beer, not just the participants - they had to get some mosquitoes, so they rounded up some anopheles gambiae mosquitoes that were present in the villages for the experiment and they read them in a lab. And they made sure that the females were going to be used, because you guys know that females are the mosquitoes that are biting, not the males.

Robert Lamb: Yeah, that's my thing. I don't have a problem with the male mosquitoes. It's the ladies that are awful.

Allison Loudermilk: It is the ladies that are awful. And why do they need the blood meal?

Robert Lamb: They've got babies to feed, right?

Allison Loudermilk: Yep, they've got eggs to nourish. So they got their female mosquitoes good and hungry. And since they're not going to be counting the mosquitoes on their participants, they had to rely on something called an olfactometer.

Robert Lamb: A smelloscope kind of thing?

Allison Loudermilk: A little bit. It's a device that labs may use to disperse an odor precisely.

Robert Lamb: Oh, okay. So it's like a stink gun if you will - a smell gun, an odor distributor?

Allison Loudermilk: Is there such a thing as a stink gun? Are you just making that up here?

Robert Lamb: I'm just trying to picture it in my head. It shoots an odor, right?

Allison Loudermilk: It directs an odor. So here's what they did. They got their beer participants - the beer drinkers and the water drinkers - and they sat them in a tent. They pointed a fan at the participants and the fan directed the body odor toward the olfactometer. And they measured the attractiveness before giving them water or beer. How are you going to measure someone's attractiveness? It's not, "Hey, he's cute. Hey, he's not. Oh, that guy really needs to do something with his eyebrows."

Robert Lamb: Because you're trying to appeal to a mosquito and the advertising industry hasn't been going after that demographic.

Allison Loudermilk: They really haven't. So they measured attractiveness with the help of the olfactometer. So you have a bunch of mosquitoes sitting at the base of this Y-shaped olfactometer. So do you have that in your head? At the tail of the Y is a box, and then you're going to have the stem of the Y coming up and then it's going to branch off into the two arms of the Y. See that?

Robert Lamb: Yeah.

Allison Loudermilk: Okay, so at first they have these mosquitoes just sitting at this base box at the tail of the Y. And they defined attractiveness by how many mosquitoes you induce to fly toward the yummy body odor smell, so to fly toward the arms of the Y. So they call that activating - how many mosquitoes you activated. And they measured this. So they would blow the odor of the beer-drinking person and the water-drinking person. How many mosquitoes are you making fly towards the arms of the Y.?

Robert Lamb: It's like a maze, right - not really a maze, but a sealed road that forks two ways. Which road are they going to take?

Allison Loudermilk: Yeah. Exactly!

Robert Lamb: The beer road or the water road. It looks like something out of The Wasp Factory. It's really cool. I think I saw a picture of it.

Allison Loudermilk: It is pretty neat. I didn't know such things existed. It seems like a pretty simple operation once you think about it. So it wasn't just how many mosquitoes you induced to fly, they had to pick the right road that you were just talking about. So are they going to orient toward the water one or the beer one? And sure enough, the researchers found that the mosquitoes oriented toward the beer one. In fact, 60 percent of them flew upwind and chose the arm with the beery odor. So mosquitoes like beer. No surprise there. So what's the big deal here? You're only going to be able to fight malaria or other insect born diseases if you know who's at risk.

In Burkina Faso, the Dolo drinking ones may be. So if you have knowledge of this risk factor, then you can help public health officials devise effective interventions.

Robert Lamb: Yeah. The thing that interests me about all of this - I find myself having this mindset that mosquitoes are just going to bite everybody and there's not any rhyme or reason to it unless you're wearing some sort of Off or are wearing garments head to toe. But it's more like a predator in the Serengeti, prowling. Anytime you watch Planet Earth or Life, you see a cheetah stalking something. What do the predators always go after? They always go after the animal they can catch, something weak. Maybe it's a wounded animal or an old one - the one that's not going to run as fast. So if you're a mosquito, you're doing the same thing.

Because you want a good meal out of it, you want to go after the large, slow, drunk guy at the party.

Allison Loudermilk: Who's not going to be able to swat you away?

Robert Lamb: Exactly. The short person who hasn't had anything to drink -

Allison Loudermilk: Yeah, that short person who's smashing the shuttlecock, doing the outdoor sports and moving all around -

Robert Lamb: No, no. If they're moving around, they might get winded.

Allison Loudermilk: Oh, that's true.

Robert Lamb: And then if you've got a winded person, they're not going to -

Allison Loudermilk: Yeah, they're moving.

Robert Lamb: So it's that small still person who hasn't had anything to drink and doesn't smell funny. It's like going next to them and trying to get a meal off of that neck, you're going to get swatted.

Allison Loudermilk: Right. So all of these cues correlate on an evolutionary level with how well a host is able to defend itself. And the people that are less able to defend themselves, the mosquitoes are going after them. And unfortunately, that means, if you're large or pregnant, or some other combination of those factors -

Robert Lamb: It brings to mind those people who are always throwing outdoor events. And you want to prevent mosquitoes from coming after people - what if some entrepreneur out there started hiring themselves out as mosquito bait? Their whole deal is, "Look, I will show up at your party and I will drink a lot of beer and run around in circles And the mosquitoes are going to come after me and you guys can just do what you want, carry on, and have a good time. And just ignore me."

Allison Loudermilk: Right. It would be like Citronella, but way more effective and entertaining. So we'd like to hear how you guys weigh out on the scale. Do mosquitoes love you? Do they stay away from you like the plague? Do let us know. Send us an email at sciencestuff@howstuffworks.com.

Robert Lamb: And we sure do get email at sciencestuff@howstuffworks.com. In fact, I see you've got two in your hand right now. Do you want to read those?

Allison Loudermilk: I'm sorry; I was just waiting for the listener mail sound effect to be given ample space.

Robert Lamb: That's a pretty cool effect. I like it.

Allison Loudermilk: Yeah. Okay, I think that was a good enough pause. So we got some email from Gretchen N. And Gretchen N. used to work for the City of Chicago's Department of Environment. And she worked on it while the Rooftop Garden was being planned and built on the city hall. So that's pretty cool. So had some inside scoop on the Chicago green roof that we were talking about in a podcast. Gretchen, however, proposed an interesting idea. She was saying that if you can't put a green roof on your house, there are other alternatives.

She writes, "When my husband and I rehabbed our house, we knew that we wanted a greener roof. So we chose a standing seam metal roof. Being metal, it naturally reflects solar energy back into space. And we included a special coating to increase the albeto. The color of the roof is champagne." Doesn't that sound nice, a champagne colored roof?

Robert Lamb: A champagne colored metal roof?

Allison Loudermilk: Yeah. "It is a reflectivity of .45 and an emissivity of .78." And of course she's found that her A/C costs have dropped significantly and the upstairs is far more comfortable.

Robert Lamb: Well, that's cool.

Allison Loudermi lk

Yeah, pretty cool, Gretchen. And she also wrote that the biggest problem she had when she was getting the green roof together was finding builders to take her seriously. If she hadn't been insistent about wanting this roof and educating the building, she probably would've wound up with asphalt shingle. So go, Gretchen - sticking to your green guns. We also heard it from a couple of you guys on our smart group podcast. And one was from Shawn, who goes by the nickname Speedy. I love that.

And Shawn wrote in to tell us that he in fact works in the electric utility field for a company that develops outage management and smart grid software. So this is the guy to go to with questions. Shawn, where were you when we were developing this podcast? And I was wondering during the podcast - I don't know if you guys remember - if businesses would be okay with electricity demand pricing. Remember, we were talking about that and speculating whether it would drive up costs and teleworking different measures?

Robert Lamb: Right.

Allison Loudermilk: So Shawn writes that, "Yeah, I can confirm that today companies will shift their operations to different times or turn off various systems to save money. In exchange, they get a discounted rate for all the power usage from the utilities."

Robert Lamb: That's cool.

Allison Loudermilk: He also writes that, "What utilities find is that when consumers are given the choice and information, they will better use power."

Robert Lamb: Excellent.

Allison Loudermilk: This ties into a blog post I want to do about persuasive technology.

Robert Lamb: Well, it also reminds of the little displays they put up on the side of the road to tell you what speed you're going. It's flashing at you if you're at or over the speed limit. And they say those are actually pretty effective. It gives you the information. And sometimes I think we subconsciously start regulating it. But if you had an actual dollar sign tied up in it, even more so.

Allison Loudermilk: And then we heard from a guy named John who wrote in with some smart grid comments. And John specifically had an idea for fighting vampire energy. He wants to make an app on the iPhone that can control the electric switches in the house while connected to your Wi-Fi. So the Wi-Fi's constantly on and the big selling point of the application he writes, "Instead of just a master switch, software's programmable." So you could program certain switches to drive off of a command on the phone and program a home this way. So you wouldn't wind up cutting the power to your alarm clock. You have to have your alarm clock on all the time. So that's pretty cool, as long as I could figure out the iPhone app.

Robert Lamb: Yeah, some of them are designed a little weird.

Allison Loudermilk: And I guess I would have to have an iPhone, too. And the last one, Bram from Manitoba, Canada was struck by a comment made about why the energy utilities are encouraging efficiency and reduced consumption of electricity at the consumer level. In Manitoba, it's a net export of electricity. So those guys make extensive use of hydroelectric power to generate electricity. And with a relatively small population, we're able to sell electricity to neighboring provinces and states. So the incentive there is built-in for Bram and his fellow folks in Manitoba. So that's pretty interesting. I did like hearing a lot about how people are experiencing smart grid and smart grid technology because it is a newer concept.

Robert Lamb: Yeah. The great thing about the feedback is that the smart grid is something that's happened. It's in the process of happening. And it's happening at various levels from the user level to the power generation level and every step in between. So we got to hear from a few different people along that long line of distribution.

Allison Loudermilk: So again, we always love to hear from you. So send us an email at sciencestuff@howstuffworks.com, or you can go to the site, too.

Robert Lamb: Yeah, check us out. We're on Facebook, Stuff From the Science Lab, and we're on Twitter as @LabStuff. And we'll keep that updated pretty much daily with our latest articles, latest blog posts, and latest podcast topics.

Allison Loudermilk: All right. Thanks for listening.

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