How a Half-Inch Beetle Finds Fires 80 Miles Away

How does a half-inch beetle find fires 80 miles away? Why, it's called 'stochastic resonance' of course! Slashdot reader bodog shares an excerpt from a report via Scientific American: The fire chaser beetle, as its name implies, spends its life trying to find a forest fire (because freshly burnt trees are fire chaser beetle baby food). [T]hey can sense fires from distances over which car stereos are hard pressed to pick up FM radio. In fact, because the infrared emission of a burning oil tank of known volume (in this case, 750,000 barrels) can be calculated with reasonable certainty, scientists that studied the Coalinga oil tank explosion have inferred the beetles can detect infrared radiation intensities so low that they are buried in the thermal noise around them. But... how?

The heat eyes on the sides of fire chaser beetles are filled with about 70 infrared sensilla. Inside each sensillum is a hair-like sensor (called a dendritic tip in the diagram above) that physically deforms when the sensillum expands in response to heat, triggering a neural response. A signal picked up by more than one of them can be summed up and amplified by the neurons that wire the [70-90] array. As a result, the heat eye can detect softer signals than a single sensor could.

Finally, it is also possible the beetles are better able to detect a signal buried in noise due to a spooky (to me) phenomenon called 'stochastic resonance.' In this scenario, added thermal noise counterintuitively helps a sensor pick up a signal. A signal below the threshold for triggering a sensor -- but still close to it -- will resonate by chance with a portion of thermal noise that is the same frequency. When there is more noise, there is more signal at that resonant frequency. Together, noise plus signal adds up to an impulse sufficient enough to trip the sensor when signal alone or signal with less noise would not. Incredibly, the measurement gets more precise in the presence of noise than without.

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