GoKawiilIn a quiet summer garden, a caterpillar perches on a branch, munching serenely on leaves. A moment later it freezes. It senses danger—and just in time. From behind, a wasp approaches, sizing up its prey.
Tobacco hornworm caterpillars don’t look like they have ears, and yet they’re able to sense predators such as wasps. How does the caterpillar know a wasp is approaching?
Scientists do not fully understand how this caterpillar’s senses work, but we are part of a team of biologists and engineers who want to figure it out. Our ongoing research suggests that tobacco hornworms can hear using tiny, supersensitive hairs on their body.
Understanding the intricate biological mechanisms that allow this organism to perceive and interact with its environment would help solve a mystery of the natural world. It could also help scientists design new, cheaper microphone technology.
Because the hornworms’ hairs are so sensitive, we have to study them in complete silence. And where better to study hearing than in the complete silence of an anechoic chamber?
What Happens in the Anechoic Chamber
What happens outside the anechoic chamber stays outside the anechoic chamber, because it is meticulously built that way. Anechoic chambers are some of the quietest places in the world. They are engineered specifically to block the entry of any undesired sounds. Heavy-duty steel springs support the “floating” chamber and keep it from touching the ground. This detachment isolates the space from outside vibrations or noise.
In such a chamber, we studied the caterpillars’ responses to vibrations. Every day for a year, we set up a caterpillar on a platform and sent vibrations toward the platform at a variety of intensities.
To measure the movement and precise vibrations that traveled through the platform the caterpillar sat on, we used a device called an accelerometer. In response to vibrations, we sometimes saw the caterpillars jump; at other times they twitched or even shuddered from the sheer physical force.
Through our observations, we pinned down the specific threshold where the caterpillars stopped reacting to vibrations. Any vibration weaker than that magnitude, and the caterpillar wouldn’t visibly react at all.
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