How Does The Insects Hear? : Can They Help Us Develop Future Hearing Aids

chotho (69)in #steemstem • 8 years ago

Taking this question, one would think : "Well, about all the ants, you probably know everything - and what, and how, and what they hear!" It turned out - nothing of the kind! For myrmecologists (as experts on ants are called), there is undoubtedly only one thing: ants know how to communicate with sounds. And if that's the case, then it means that they have a hearing and organs that are (with a pretty big stretch) can be called ears.

And the "ears" of ant do not resemble what we are accustomed to call this beautiful word. And the "ears" of these several species. And hearing is by no means their only function. And they are located not only on the head, but also ... Okay, about everything in order.

As you know, sounds can spread not only through the air, but also through the liquid (for example, water) and even over solids (for example, soil, tree trunks and leaves). And if "air" sounds are more important to people, "hard" sounds are of great importance for ants that crawl all over their land, trees and other solid things. (In principle, a person is also able to hear "hard" sounds.)

And in order to recognize such "solid" sounds, one must be able to perceive vibrations, vibrations of the substrate. And for this there are not enough two ears on the head - the hearing organs should be located wherever only the body comes into contact with the "sounding" surface, that is, practically throughout the body.

Three-dimensional reconstruction of the subgenual organ of the left middle tibia of the lacewing C. carnea. BC, blood channel; C, cap; CC, cap cell; CU, cuticle; S1, S2, S3, three scol-opidia; SC, scolopale cell; SE, sensory cell; TR, trachea; V, velum.
Scolopidia, like strings, are stretched between the cuticle and the flexible membrane. When the cuticle shifts, it pulls the skolopidia behind it and causes the excitation of the neuron located in this skolopidia.

In structure, these organs also do not look like the ears of people or, say, rabbits. Since they should not perceive the waves flying in the air, they absolutely do not need that external "trap" in the form of a shell, which we are accustomed to call an ear. And these auditory organs consist of original "strings" (they are called skolopidia) stretched between the cuticle (the outer skeleton of the insect) and a special flexible membrane. Each skolopidia consists of three cells, one of which is a nervous one. If the surface, to which the ant touches, will begin to oscillate, then the cuticle will begin to pull the skolopidia. When the skolopidium stretches, the nerve cell under the influence of tension is excited and sends a pulse to the corresponding nerve node. Thus, the vibrations of the surface are transformed into nerve impulses, and the ant hears a sound. The organs described above are called chordotonal organs and are engaged not only in the discrimination of sounds, but also in proprioception - that is, they feel the stretching of the muscles and determine the position of the body in space.

So, with "solid" sounds, we sorted it out. But does the ant also hear "airy" sounds? There is no unequivocal answer to this question, however, it is possible to extrapolate to ants the data obtained on other insects - for example, mosquitoes and flies.

And flies and mosquitoes can hear "air" sounds with the help of special bristles located on the antennae. The sound wave moves such a seta, the bristle pulls behind the skolopidia, from this the neuron located in the skolopidia discharges and sends an impulse to the nerve bundle. Such organs of hearing are called johnston organs. They are a subtype of chordotonal organs and are sensitive only in the near field (usually at a distance of not more than tens of centimeters). It is easy to understand that they will feel not only sounds as such, but also any fluctuation of air - for example, a wind caused by an approaching fly swatter.

And besides, insects have another kind of sense organs capable of perceiving sounds - trichoid sensillas. This complex word combination is called tiny setae on the body of an insect. These bristles are directly connected to the nerve ending directly (and not through the scolopidia, as are the johnstones organs), and when the sound wave (or simply the wind) vibrates the trichoid sensilla, the nerve end is excited and generates a pulse, and as a result, information about the oscillations reaches the corresponding nerve node . Ants have trichoid sensilla, but whether they are sensitive enough to perceive sounds has not yet been fully clarified.

Fig. 2. Antennae of ants (electronic microphotography). On the antennae there are johnstones organs, as well as many trichoid sensilla, but it is not known whether they are sensitive enough to hear sounds. The length of the scale ruler in the upper figure is 500 μm, at the bottom - 200 μm.

But something is known about how ants use sound alarms.

For example, ants-campontus ants, or woodworms, gnawing their nests in wood, hit their jaws or belly on the walls of the nest to call relatives to protect it.

And many ants know how to chatter, rubbing their abdomen on special "graters" on the stalk between the chest and abdomen (Figure 3). The chirrup sound is barely audible, the human ear hardly discerns it even at close range. However, ants of such loudness are enough, and they perfectly can communicate with each other by means of chirring.

Fig. 3. Most ants make sounds with the help of friction of the abdomen (Gaster) on the stalk (Postpetiole)

For example, this chirping is transmitted through the soil. Kindred I can dig out the ant, buried in the sand, after hearing his "screams for help."

And through the leaves and branches of the trees, vibration from chirping is also transmitted. This is used by some ants in a very unexpected way. It turned out that in leaf-cutting ants, the vibration of the abdomen is transmitted to the jaws (mandibles). When mandibles cut a leaf, they vibrate at a frequency of about 1 kHz (a thousand times a second!). Due to this, the sheet is cut if not faster, then more evenly and accurately.

And later it turned out that the ants more often rattle, when they cut no more hard, and more delicious leaves! It turned out that at the same time smaller workers run up to larger worker ants. Then a large worker drags the cut sheet into the anthill, and the small ones climb onto the sheet and ride it. But they do not just skate, but, for example, protect the porters from flies trying to put their testicles on the body of large workers.

Recently it became clear that sounds for communication are used not only by ants, but also by their parasites. In an anthill, hundreds of species of other insects usually live. Among them - the caterpillars of some butterflies-pigeons. These caterpillars are similar to the larvae of a certain type of ants in appearance, and most importantly, by smell. Working ants, having found such a caterpillar, drag it into the nest. The caterpillars of some species continue to imitate larvae so well that the labor ants feed them as their own younger sisters (working ants are barren females and larvae are their sisters).

Recently it was found out that caterpillars and pupae of "pigeons-cuckoo" make sounds, imitating adult ants. In this case, as it turned out, in the ants-owners (one of the species of the genus Myrmica), the uterus and worker ants chatter differently. If you play the sounds produced by the uterus, they surround the source of sound and take characteristic "protective" poses, as if they guard the real uterus. Sly caterpillars and doves' dolls imitate exactly the sounds of the uterus, and the working ants rush to guard them!

Conclusion

This example shows that sounds can play an important role in the life of the ant family: in particular, the royal "well-placed voice" helps the uterus occupy the highest level in the hierarchy. So, the ants well distinguish the different sounds of their relatives - whatever they hear ...

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