The woods on a warm night are rowdier than a busy bar: Cicadas sing, frogs bellow, owls hoot. Practically every creature around is announcing its presence as loudly as possible in the hope of attracting the attention of the opposite sex. And if you're a tiny cricket, you've got to find a way to make yourself heard above the racket.
Male crickets do this by restricting their chirps to a single, specific frequency. Like radio listeners who know exactly what station they want, the ears of females are uniquely tuned to resonate at that same frequency. This lets them navigate the noise and find each other.
That is, until the frequency changes.
Scientists have known for a while that the frequency of cricket songs depends on temperature. It's a basic law of chemistry: Chemical reactions happen faster when they're hotter. And because insects are cold-blooded, meaning that they don't regulate their own temperatures, every reaction in their body is dependent on the weather outside. On warm days, their muscles are quick and responsive. On cold ones, they'll be lethargic.
For this reason, crickets — which produce their chirps by rubbing their wings together — will make a higher-pitched sound when it's hot out. The phenomenon is so reliable that someone with a well-trained ear can use the critters as thermometers: You can count the rate of chirps (which also increases when it's warm) and calculate the temperature from it. How's that for a cool party trick?
But it would likely seem less amusing to lady crickets, who would be met with radio silence on date night if they couldn't adjust to the frequency change. But as it turns out, tuning into a new station is no problem for them.
In a study in the journal Biology Letters, researchers report that females from the North American tree cricket species Oecanthus nigricornis re-tune their ears according to the temperature so they can hear their male counterparts.
The secret to the females' flexibility lies in their brains.
Like humans, crickets have neurons (brain cells) whose job it is to filter out important sounds and amplify them. Problems with those cells are what sometimes cause a person's ears to ring. But when they're working, "they actually improve your perception of sound," explained lead author Natasha Mhatre, a postdoctoral fellow studying sensory biology at the University of Toronto.
In crickets, "the sounds that they amplify are the sounds of their own species," she continued. "And we found that they can change the frequency that is amplified depending on temperature, and that’s how they keep up with the males."
This adjustment happens at the cellular level, suggesting that it's entirely unconscious. And it's likely that the shift happens for the same reason that the males' singing speeds up: The cells are able to work faster when they're warm, so they amplify higher frequencies.
It'll take further study to determine if that's really what's happening. But Mhatre says that the results could help us understand how crickets are affected by changes in the temperature and noisiness of their environments.
"There are these networks of communication that insects have built up," she said. "We want to know how these networks might be disturbed."