Do flies dream of wireless sheep?

September 30, 2008 8:46 PM

Why, of all places, houseflies seem to be irresistibly attracted by wireless antennae?

WeirdEntomologyFilter: fall has just begun, and as usual this year's houseflies move inside my house (kitchen, mostly) for warmth and yummy fly bits. Ok, fine, I'm not particularly squeamish and it's nothing a rolled newspaper can't take care of should the little pests become more annoying than usual. All foods are wrapped and stored in fly-safe places, so there's no particular worries about the hygienic side of it (and, we're talking small numbers anyway).

In the last few days, however, I noticed a pattern of behavior that is - at least to me - startling: besides the obvious grain of sugar or drop of honey falling on the table during breakfast, they seem to be attracted - no - irresistibly attracted by the small USB wireless key that protrudes from the laptop that usually sits on the kitchen table.
It's their favourite hangout, apparently, where they go for brief rests, long snoozing, and - ahem - the occasional quickie (turns out the little bastards are quite active). There's usually one or two on it at any moment. The approx 2-inch long, white plastic key is starting to gross me out, as it's being covered in tiny fly droppings (which are regularly cleaned with alcohol). I'll probably try and spray the dongle with a bit of repellant (though I'm fairly certain that the plastic casing won't appreciate the solvents and oils involved).

However, the question is: are flies attracted by electromagnetic fields? If so, have you noticed similar behavior? And, is it only the wireless range of frequencies or do they have other preferences? (An FM radio in the same room is largely ignored).

(the laptop is a Toshiba, running XP Pro Sp2)

posted by _dario to home & garden (11 comments total)

You aren't the only one who's noticed this in insects. Ants really like electrical equipment, for example. There's an article from Wired that also mentions the phenomena. Nobody really knows for sure what's going on and why, although in some cases insects just appreciate the darkness and warmth of computing equipment.

It's entirely possible that your wireless antenna is attracting the flies, yes.

(These are older articles, yeah. It's entirely possible this has been solved or studied since then.)
posted by truex at 9:07 PM on September 30, 2008

Antenna are capacitors. The transmitter pumps charge into and out of them, and among other things, this will cause them to vibrate. There may well be a lot of harmonics in the vibration, and I wonder if one of them is an audio frequency which attracts insects?
posted by Class Goat at 9:40 PM on September 30, 2008

Here's a decent way to determine if the flies care about the RF properties of your device, or if they just like your sticky finger goo or the smell of the rubber and plastic on it: Do they hang out on the antenna of your wireless base station / AP / router?

I've never seen the behavior in question -- including the ant thing -- and I have a good sized handful of 2.4GHz devices in the house and plenty of miscellaneous electronics. I'd be much more inclined to believe there's a chemical attractant of some kind at work here, rather than EM radiation.
posted by majick at 10:30 PM on September 30, 2008

I'm wondering if it isn't outgassing from whatever plastic/material the antenna is made from. One test would be to see if they're still attracted to the device when it's powered down.
posted by dws at 10:44 PM on September 30, 2008

Just to make clear, I don't think they're attracted to the RF. I'm suggesting that they might be attracted to high-frequency sound.

But there's no chance they can hear 2.4 GHz. Not possible, even for insects. There might be a lower frequency harmonic produced by the antenna that they pick up, but the harmonic pattern would depend on the antenna design, and antennas on the base station might not produce it.

I agree that it would be interesting to know if they're also attracted when the power is off.
posted by Class Goat at 11:42 PM on September 30, 2008

I'm betting that they will continue to be attracted for maybe a couple of minutes after the power goes off. I'm betting this on the grounds that I've noticed my PCMCIA wifi card runs quite warm. I think they're probably attracted to the smell of warm plastic.
posted by flabdablet at 12:22 AM on October 1, 2008

They probably like it simply because it's warm.
posted by ZaneJ. at 12:42 AM on October 1, 2008

No answers from me, just an observation: the flies in -my- house all congregate on and around the porcelain hanging pull cord thing on my ceiling light. There can be 10 of them dancing around their little disco ball. Kind of annoying, really.
posted by tingting at 6:03 AM on October 1, 2008

The frequency of many wireless systems is close to that of microwave ovens. Flies are notoriously sluggish in the cold.

I think they're sitting on the antenna to take advantage of the the direct heating effects of the RF.
posted by jamjam at 8:40 AM on October 1, 2008

When it comes to resonance, "close" doesn't count. Microwave ovens work because they broadcast a resonant frequency of water molecules.

Also, the power level is too low. You won't get any noticeable heating from a 50 milliwatt transmitter, even if the frequency was correct.
posted by Class Goat at 12:17 PM on October 1, 2008

You are mistaken about microwave ovens and microwave heating in general, Class Goat:

Microwave heating is sometimes explained as a resonance of water molecules, but this is incorrect: such resonance only occurs in water vapor at much higher frequencies, at about 20 gigahertz[5]. Moreover, large industrial/commercial microwave ovens operating at the common large industrial-oven microwave heating frequency of 915 MHz (0.915 GHz), also heat water and food perfectly well.

As to your second point, a typical human generates an average of about 90W, or a bit more than a microwatt per milligram. A typical housefly might mass around 10 milligrams, and assuming the figure you offer for the wattage of the antenna is more reliable than your understanding of microwave ovens, a fly would only have to absorb around 1/50,000th of the RF output of that antenna to get !0% of the energy it would get from its own metabolism if it were composed of human tissue (although the metabolic rate of even a resting fly is probably much higher than that), and quite a bit less than a 10% boost seems to me to have a chance of being something a cold housefly might seek out.
posted by jamjam at 3:51 PM on October 1, 2008