Some people feel uneasy at the mere mention of insects, squirming in their seats or even jumping away in fear. But can insects hear our screams when we encounter them. The answer is yes. Some insects can hear, and in some cases their hearing organs are surprisingly similar to those of humans.
The hearing abilities of insects vary greatly, as does what they are able to detect. Mosquitoes can hear from a distance of about one meter, while crickets can detect sounds from up to a kilometer away. Praying mantises can hear ultrasonic sounds, while crickets are sensitive to low frequency tones. Insects hear what they need to hear, and evolution has provided each species with the tools required for survival.
The first insect to move onto land around 400 million years ago was likely deaf. From this ancestor evolved more than 900,000 insect species. Most remained deaf, but some developed the ability to hear sounds carried through the air. Over time, different insect groups found different solutions to hearing, driven by two main needs. One was communication across long distances, and the other was the ability to detect predators and escape them.
In grasshopper related insects, hearing first evolved as a means of communication. Fossils from around 165 million years ago show that the ancestors of crickets already had hearing organs that allowed them to detect mating calls from afar.
Crickets developed hearing for communication long before they needed it to detect predators, since bats only appeared around 65 million years ago. This sequence influenced the evolution of cricket hearing mechanisms and likely affected the development of hearing organs in mantises, beetles, bees, and butterflies as well.
Although hearing evolved independently many times during insect evolution, most insects are still deaf. For example, out of approximately 350,000 beetle species, hearing evolved in only two. Many beetles communicate using vibrations, but most cannot hear airborne sounds.
In insects, the process is somewhat different. What all insect hearing organs share is a series of receptors stretched along the insect body called chordotonal organs. These organs normally detect position and relative movement of body parts, but evolution adapted some of them to sense vibrations caused by sound waves.
During evolution, one pair of chordotonal organs was converted from position sensing organs into hearing organs. Because the selection of which pair would become hearing organs occurred randomly and independently in different insect groups, hearing organs appear in many locations across insect bodies. Mosquitoes, midges, honeybees, and flies developed hearing organs on their antennae.
Net winged insects have ears on their wings, while crickets and grasshoppers carry hearing organs on the front of their bodies. Certain parasitic insects developed hearing organs near their necks to better locate where to lay their eggs on a host. Some insects converted more than one pair of chordotonal organs into hearing organs. A remarkable example is a grasshopper species that carries six pairs of hearing organs on its abdomen.
For chordotonal organs to function as hearing organs, they needed a structure capable of responding to sound vibrations. Over time, insects evolved two such mechanisms. One involves antennae that move in response to sound waves, and the other involves a thin membrane similar to an eardrum that vibrates due to pressure differences.
In most insects, the eardrum is located between two air sacs. An exception can be found in certain grasshopper relatives, where the eardrum sits between an air sac and a fluid filled sac. This structure is remarkably similar to the human ear. In moths, the eardrum developed not as a thin membrane but as a plate like structure made of overlapping scales that can detect vibrations and transmit them inward.
Some grasshopper relatives possess the smallest known ears, with one located on each front leg just below the knee. These tiny ears allow them to detect mating calls, locate food, and even identify bats by the sounds they emit.
One species found in Australia uses its hearing in a particularly clever way. It lures male cicadas by mimicking the mating calls of female cicadas during their courtship duet. This trick requires the insect to recognize complex sound patterns and produce them with precise timing.
Despite their small size, these ears are complex and unique, and surprisingly similar to human ears. Researchers using advanced imaging techniques were able to reconstruct the hearing system of one such insect and discovered two previously unknown structures. One is a small rigid plate located behind the eardrum, and the other is a fluid filled tube lined with sensory receptors.
By using laser techniques to simulate sound vibrations striking the eardrum, researchers showed that the small plate transfers vibrations from the eardrum into the fluid within the tube. This mechanism closely resembles the way human ear bones transfer vibrations from the eardrum into the fluid filled inner ear.
Evolution has experimented with many different ways of building ears in insects, resulting in an astonishing variety of structures and mechanisms. Many insects produce sounds beyond the range of human hearing, which is why we often ignore them entirely. Although insect hearing organs are difficult to detect, they are no longer invisible. With new tools and advanced technologies, the complex world of insect sound is gradually being revealed.