It’s July in Minnesota, and you know what that means: bugs. Clouds of bugs. Some people complain, but I generally rationalize a large population of fecund invertebrates as simply a sign of a healthy ecosystem, so yeah, we’ve got bugs, but it’s good for us.
Except for those mosquitoes. It’s hard to think charitably of some invertebrates when you’re lying in bed at night and you hear…that…high-pitched whine rising as the nearly invisible little blood-sucker buzzes by your exposed flesh. Now, in a discovery calculated to increase my irritation, I learn that the little bastards are singing a love song as they hover about, looking for an opportunity to stab me and suck my blood. “Come to me, come to me, mon chéri,” they sing, “after I gorge myself on ze fat, torpid hu-man (and daintily spit up a little backwash into his capillaries), we shall make sweet, sweet love in the moonlight and zen I shall lay a thousand eggs, and our progeny shall feast on his children!” (Sorry, but now whenever I hear them they’ve also got a silly Pepe LePew French accent.)
Here’s how you figure this out. With a tiny drop of sticky beeswax, tether a mosquito to a thin steel wire, and lift it into the air. When its feet have left the ground, it will spontaneously start flapping its wings, making its usual whine (you can stop them just by bringing a piece of paper into contact with the legs, so that it is fooled into thinking it has landed.) In the photo to the right, you’ll see a small, blocky microphone mounted within a few centimeters of the beast. Easy—now you can make a mosquito buzz at will, and get high quality recordings.
Now the interesting part: the mosquito whine is variable, and they can change the pitch by modulating the wingbeat frequency. How do you get them to change the pitch? By playing musical tones at them. It’s true: in a perverse variant of the closing scene of Close Encounters of the Third Kind, scientists are talking with mosquitos by playing tones at them, and the mosquitos are talking back by changing the tone of their whine. No word is yet available on any translations, but I suspect it will be some variations on “blood” and “sex,” emphasis on the sex.
Another thing they can do with this rig is record the conversations between mosquitoes. In the recording below (tres creepy if mosquito whines make your skin crawl), a tethered female is singing along at about 370Hz, and after about 5 seconds, a tethered male is launched nearby. His “voice” is higher pitched than hers at 595Hz, but almost immediately you’ll hear him try to sound huskier, while she raises her pitch a little bit, so that soon enough they’re singing at almost the same frequency (not quite, though—you can also hear the beating as they aren’t quite in perfect tune.)
This only works well if the two mosquitos are of different sexes. Put two males in the air at the same time, for instance, and you get a recording like the one below.
The two males first converge on the same frequency, but then after a period of anarchic oscillations, they diverge. I found the sound files difficult to pick up on that behavior, so I think us visual animals can see it better in the graphs of frequency below (D is the spectrogram of this recording).
Different sex pairs sing in harmony together, but same sex pairs don’t; something clues them in about the gender of their partner from their song, which is curious, since both sexes can converge to the same frequency. The authors speculate that the key difference is responsiveness. Males respond much more quickly, but not instantaneously, to the pitch of their partner; females are slower and are in no hurry to respond.
What this means is that when two males meet, they try to synchronize, but they react to what their partner was doing just a moment before. Their “voices” dart up and down, each trying to meet the other, but never quite doing it. Two females, on the other hand, will slowly harmonize, but when one drifts away from the common frequency, the other may take a few seconds to try and match up. Their “voices” wander away from other other in slow rhythms. The only stable convergence is to match up a fast male and a slow female, where the male can rapidly lock in to her frequency, and she isn’t reacting quickly to his frequency shifts.
Two mosquitoes don’t have to actually see each other, they just sing at each other…and if they find they can make beautiful music together, they know they’re sexually compatible and should hook up. I think that’s beautiful, but I’m still going to crush their blood-sucking insectile bodies between my hands if I can catch them.
Gibson G, Russell I (2006) Flying in Tune: Sexual Recognition in Mosquitoes. Curr Biol 16:1311-1316.