Drawn to Flame: Fire Beetles Sense and Seek Out Wildfire

Biological Strategy

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Respond to Signals

To interact with its environment, a living system must not only sense a variety of signals, but also respond to them. To be energy- and material-efficient, those responses must be appropriate to the signal. This generally requires sensing thresholds to trigger an appropriate level of response (for example, hiding under a shrub versus running away to avoid a predator). Response strategies are tied to a specific signal and often have a response threshold, which determines how strong a signal must be to warrant expending energy to respond. One example is a plant that lives in arid regions in South Africa. Its seed capsules remain closed until rainfall triggers them to open to release the seeds. But the plant only responds to a second rainfall, thus protecting against releasing its seeds before there is enough sustained water for them to grow.

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Navigate Over Land

Organisms that navigate over land must avoid obstacles and find their way from one point to another. Because land lies at the interface of the ground and air, these organisms have the opportunity to use signals transmitted through both the ground or air, rather than relying on one potential source. To take advantage of this opportunity, these organisms must have strategies attuned to diverse signals, which may travel through multiple media. An example of an organism that navigates over land is a desert ant in Tunisia that senses smells from two different directions at once, forming a “mental map” of its surroundings.

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Navigate Through Air

Although free from many of the physical obstructions found on land and in water, organisms that move through the air must still avoid hitting each other and objects in their flight path, such as trees and mountains. They also need to navigate from one place to another, which presents a different challenge. They use one strategy to navigate around obstructions and another to move towards their destination. For example, bats use echolocation to detect both obstacles and prey. To navigate during migration, bats also use vision, sun orientation, and likely other strategies.

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Sense Temperature Cues From the Environment

Some living systems use their ability to perceive temperature to find prey or avoid predators, or as a way to gain information about their environment, such as whether they are near a warm or cold place. Temperature gradients can be subtle and modulate as they travel through water, air, or solids. Living organisms must therefore have a variety of thermal sensors appropriate to a given medium (liquid, gas, solid). Some even have a way to “visualize” a signal’s source. For example, the rattlesnake has heat sensors with thousands of nerve endings located in pit-shaped holes on each side of its face. The sensitivity of the pits overlaps, giving the snake a bifocal image of the heat’s source.

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Sense Light (Non-visible Spectrum) From the Environment

Living systems interact with each other and with their environments to gain information. Sometimes that information is in the electromagnetic spectrum. Wavelengths in the electromagnetic spectrum are also called the non-visible spectrum, because humans can’t detect them with the naked eye. These include ultraviolet (UV) light, infrared (IR) light, radio waves, and other wavelengths. Detecting within these spectra requires strategies beyond those used for visible light, so many living systems that depend on these signals have specialized organs to do so. For example, beetles that feed on burned trees have sensory organs that detect infrared radiation emitted by fires, enabling them to quickly locate a burned area.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Melanophila fire beetles find freshly burned wood by detecting wildfires from over 20 kilometers away using heat sensors on their bodies.

Introduction

In the quiet shadows of conifer forests, the Melanophila beetle waits––not for calm, but for fire. While most flee from flame, this beetle is drawn to it. It is one of nature’s rare fire-chasers, a black-winged visitor that appears only when trees have burned and smoke still lingers in the air. Fires that destroy the lives of many open the doors to opportunity for these insects, whose young require scorched wood to survive. What appears to be ruin becomes renewal, a cycle carried forth by heat and ash and wings.

The Strategy

Fire beetles of the genus Melanophila possess a rare and astonishing sensory ability: they can detect infrared radiation––heat itself––from vast distances, often exceeding 20 kilometers. These beetles are almost never seen in untouched forests, but as soon as fire sweeps through a stand of conifers, they arrive in swarms. This extraordinary behavior is made possible by a pair of specialized infrared (IR) sensory organs located on their thorax, near the base of their legs.

Each IR organ is densely packed with tiny, dome-shaped structures called sensilla. At the base of each sensillum lies a sensory nerve cell. When infrared radiation from a fire reaches the beetle, it is absorbed by the outer cuticle of these domes. The absorbed energy heats the small, water-filled interior of each sensillum. As the water expands from the heat, it causes the dome to physically deform. This deformation mechanically activates the nerve cell at its base, sending a signal to the beetle’s central nervous system. In essence, Melanophila beetles “feel” fire at a distance––not through vision or smell, but through exquisitely sensitive mechanical detection of heat-induced expansion.

This system gives the beetles what functions like a biological thermal camera, allowing them to locate fresh burn sites ideal for laying their eggs. The larvae thrive in charred wood, which offers reduced competition and fewer predators. By wiring their reproductive strategy to a precise environmental trigger, fire, these beetles turn disaster into opportunity, cycling life forward from the ashes.

The Potential

The sensory adaptations of Melanophila fire beetles could inspire a new generation of wildfire detection technologies. By studying the beetle’s infrared sensors, engineers might design low-power, highly sensitive heat detectors that can be deployed in remote forests to detect fires in their earliest stages. Their ability to locate heat sources across vast distances also holds promise for improving compact thermal imaging systems, distributed sensor networks, and autonomous fire-seeking drones. As climate change accelerates the frequency and severity of wildfires, nature’s own fire-chasers may hold the blueprint for tools that help us live more safely alongside fire.

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