A sensitive infrared detector based on the iridescent wing scales of the Morpho butterfly is reported in Nature Photonics this week. The work could help guide future designs of thermal imaging sensors. Infrared thermography is used in industrial, military and medical applications to visualize the heat emitted from an object. Radislav Potyrailo and colleagues report a bio-inspired sensor that is faster, smaller and more sensitive than today’s infrared detectors, which often require thermal management and rely on complex microfabrication techniques. In their detector design, the team combined the relatively recent technology of carbon nanotubes with the five-million-year-old iridescent features of the Morpho butterfly wing. They found that when infrared radiation hit the wing, the air-filled photonic nanostructures heat up and expand, which causes the wing colour to change. By doping the scales with carbon nanotubes they show that the amount of radiation that the wings can absorb increases, therefore improving the device’s sensitivity.