Fire Chaser Beetles Sense Heat from Miles Away

Melanophila acuminata use infrared receptors to seek out nearby fires in order to lay eggs in scorched bark.
Courtesy of AG Prof. Schmitz/Wikimedia Commons

When a forest fire starts, first responders will rush to the scene hoping to tame the flames and direct the blaze away from populated areas. But often when they arrive they find that they’re not the only ones moving towards the blaze. Beetles of the genus Melanophila, commonly known as fire chaser beetles, are attracted to forest fires because they use freshly burnt (and sometimes still-smoldering) wood to lay their eggs.

While a charred forest may lack the vital resources that most species need to survive, for fire chaser beetles it’s an ideal place to hatch the next generation. Here, eggs stand little chance of being disturbed by predators that have fled the forest. Beneath the blackened bark, the beetle larvae will grow, hatch, and thrive.

Pit organs on the beetles’ thorax, the middle section between head and abdomen, contain highly sensitive infrared receptors that can detect heat up to 80 miles away.
Courtesy of U. Schmidt/Flickr

Fire Alert System

How are Melanophila beetles able to arrive so quickly after a fire has begun? They possess two sensory pit organs on their thorax that contain infrared receptors. Inside each receptor is a small pocket of water that expands when heat is detected, triggering a nervous system response to follow the heat source. Even when a fire isn’t emitting smoke, the beetle is able to detect its heat signature—sometimes from a great distance.

Long-Distance Detection

In a 2012 study published in the journal PLoS ONE researchers Helmut Schmitz and Herbert Bousack set out to uncover just how sensitive the beetles’ infrared reception was by examining records from a historic 1925 fire, which attracted “untold numbers” of Melanophila beetles according to contemporary observers. That year, a lightning strike ignited a 750,000-barrel oil storage tank at a reservoir facility in Coalinga, California, which is located in an arid region a considerable distance from any forest. The flames reportedly reached as high as 500 feet, could be seen 30 miles away, and burned for two days.

The researchers found that the beetles that swarmed the scene could have traveled from two areas: a forest near the San Benito Mountain Natural Area about 16 miles away or from the foothills of the Sierra Nevada almost 80 miles away. By calculating the amount of smoke along with the flame height and visibility, researchers concluded that the beetles must have used their infrared receptors to detect the fire, and that the majority traveled dozens of miles from the forests in Sierra Nevada.

Learn more about the senses of different species in our new exhibition Our Senses: An Immersive Experience.