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Why Are Mosquitoes So Attracted To Me?

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The almost 3,000 species of mosquitoes in the family Culicidae (of the 150 found in North America, 63 call New Jersey home, which makes NJ the mosquito capital of the country) have been around for over 30 million years. During that time they've become highly specialized in seeking out and feeding on blood, from which females get the protein and iron required to develop eggs (males don't drink blood, and for sustenance, both sexes feed on nectar).

Mosquitoes have chemical sensors that can pick up carbon dioxide and lactic acid from up to 100 feet away. Once they've been tipped off that there's someone or something breathing nearby, they follow their noses to hone in on their prey, insert their proboscis and begin feeding. Their saliva contains a grab bag of proteins that affect blood vessel dilation, blood clotting and platelet aggregation, which makes grabbing a meal easier, but also leaves us with red itchy "bites" (though they don't actually bite us, it's more of a stab than anything) as our immune systems break down these proteins.

They Love You, They Really Love You

After a summer barbecue, does it seem like you're covered head to toe by these bites while people who were sitting right next to you only have one or two? It's not paranoia, because the "˜skeeters actually are out to get you.

Remember when I said that mosquitoes follow their nose to you? I wasn't just being cute. I meant that they actually use an odor-based navigation system to find suitable victims. Proteins in their antennae, heads and noses latch on to chemical compounds emitted from our skin, and some of us just happen to give off odors that they find simply irresistible.

And the person sitting next to you, laughing silently as you get eaten alive? They're not special, they just smell different. Their body emits chemical compounds that make them unattractive to mosquitoes either by acting as repellents or by masking the compounds that mosquitoes would find attractive (we're not sure which way it goes, yet, but those intrepid entomologists are looking into it).

Scientists at Rothamsted Research (an agricultural research center in the UK) are also working to figure out which odors attract mosquitoes and which ones repel them. Thus far, thirty chemical compounds that definitely turn mosquitoes off have been identified and may be the key to the next wave of bug sprays.

This question was asked, during a fit of scratching, by my girlfriend Erica. If you've got a burning question that you'd like to see answered here, shoot me an email at flossymatt (at) Twitter users can also make nice with me and ask me questions there. Be sure to give me your name and location (and a link, if you want) so I can give you a little shout out.

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iStock // Ekaterina Minaeva
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Why Your iPhone Doesn't Always Show You the 'Decline Call' Button
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When you get an incoming call to your iPhone, the options that light up your screen aren't always the same. Sometimes you have the option to decline a call, and sometimes you only see a slider that allows you to answer, without an option to send the caller straight to voicemail. Why the difference?

A while back, Business Insider tracked down the answer to this conundrum of modern communication, and the answer turns out to be fairly simple.

If you get a call while your phone is locked, you’ll see the "slide to answer" button. In order to decline the call, you have to double-tap the power button on the top of the phone.

If your phone is unlocked, however, the screen that appears during an incoming call is different. You’ll see the two buttons, "accept" or "decline."

Either way, you get the options to set a reminder to call that person back or to immediately send them a text message. ("Dad, stop calling me at work, it’s 9 a.m.!")

[h/t Business Insider]