Long-range Hearing Without an Eardrum

brown and black mosquito on yellow surface

Biological Strategy

Mosquitoes

Alexandra Ralevski

Image: Nitin Chandra / Flickr / Some rights reserved

Sense Sound and Other Vibrations From the Environment

For living systems, sensing sound and other vibrations is important for communicating and detecting conditions within their environment. Living systems must locate a signal’s source so that they can move toward it (such as when it is food or a potential mate) or away from it (such as when it is a predator). To prompt an appropriate response, living systems must sense these signals, recognize their amplitude or volume (which is sometimes very low), and determine their direction. Living systems must be attuned to signals relevant to them and able to distinguish these from irrelevant sounds to avoid expending unnecessary energy. For example, owls’ ears are asymmetrically placed. This enables them to detect sounds more accurately, which helps them locate small prey at night and avoid wasting energy chasing down irrelevant sounds.

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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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Mosquitoes use fine hairs to hear sounds up to 10 meters (32 feet) away

Insect antennae are important non-visual sensory organs. Mosquitoes use their antennae as movement receivers that respond to oscillations of air particles within the insects’ surroundings. This is auditory sensing, also known as hearing. Male mosquito antennae are particularly well-adapted to detect sound as a means of finding mates. They can specifically recognize the frequency of female mosquitoes’ wing beats while flying.

Structurally, mosquitoes have two antennae beneath their eyes, each with two segments. The primary segment in males is composed of a ‘plumose’ shaft, meaning it is coated in long, feather-like fibrils or hairs. These hairs are shorter at the tip of the shaft and increase in length toward the rear. The primary segment is connected directly to the secondary segment, which holds the Johnston organ. The Johnston organ is a spherical base, densely packed with neurons. This bundle of sensory receptors is extra sensitive to the forces acting on the shaft hairs. When the hairs are moved, the forces are immediately transmitted and recognized by the sensitive neurons in the Johnston organ.

It was previously believed that organisms required ear drums for long-range hearing (up to several meters away). Ear drums work by picking up pressure from sound waves and relaying that information to the brain as sound. Because mosquitos such as the Aedes aegypti have antennae instead of ear drums, it was thought that mosquitoes could only hear sounds at close distances (a few inches or several centimeters away).

It is now known that mosquitoes can hear sounds as far away as 10 meters (32 feet). They hear best in the frequency range between 150 to 500 hertz, which overlaps well with the frequencies of female mosquitoes in flight.

The mosquitoes’ frequency range for hearing also overlapps with human speech. The most energetic frequencies of an average human vowel are in the range of 150 to 900 hertz, so they technically should be able to hear people speaking. However, there is currently no evidence that they use this to locate and hone in on people. It is well known that mosquitos pick up sensory cues such as carbon dioxide, odors and warmth to locate people.

This research offers the opportunity to develop highly sensitive directional microphones and hearing aids. All microphones and sound detection equipment are based on capturing sounds by detecting pressure differences, similar to ear drums. A microphone designed based on how a mosquito hears would detect fluctuations in air velocity, and could be designed as a fine hair or fiber for detecting sound.

Story source: Cornell University

Antennae Sense Vibrations

The antennae of male mosquitoes sense vibrations via fine, hair-like structures that respond to oscillations of air particles.

Image: A.J.E. Terzi / CC BY - Creative Commons Attribution alone

V0022549 A mosquito (Aedes aegypti). Coloured drawing by A Credit: Wellcome Library, London. Wellcome Images [email protected] http://wellcomeimages.org An mosquito (Aedes aegypti). Coloured drawing by A.J.E. Terzi. By: Amedeo John Engel TerziPublished: - Copyrighted work available under Creative Commons Attribution only licence CC BY 4.0 http://creativecommons.org/licenses/by/4.0/

Image: E. A. Goeldi (1905) / Public Domain - No restrictions

Last Updated November 3, 2020

References

Journal article

The Long and Short of Hearing in the Mosquito Aedes aegypti

Current Biology Volume 29, ISSUE 4, P709-714.e4 | 18/02/2019 | Gil Menda, Eyal I. Nitzany, Paul S. Shamble, Amelia Wells, Laura C. Harrington, Ronald N. Miles, Ronald R. Hoy

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