The ability to produce sounds is widely spread among beetles. Acoustic communication is an important means of communication of individuals of one species (signals of identification, call, alarm and threatening). By means of sounds meeting of males and females is provided, reproductive isolation in close species is achieved, intrapopulational and intrafamily relations are maintained. In contact with other species sound signals perform more specific functions of repelling or threat. In his concise review of sounds in Coleoptera R.A. Crowson (1981) mentioned representatives of nearly two dozens of families (Carabidae, Hygrobiidae, Dytiscidae, Hydrophilidae, Silphidae, Lucanidae, Trogidae, Acanthoceridae, Passalidae, Geotrupidae, Buprestidae, Anobiidae, Tenebrionidae, Cerambycidae, Chrysomelidae, Attelabidae, Curculionidae, Scolytidae), omitting from the widely known examples only Scarabaeus and click beetles. He refers several times to detailed and more exhaustive reviews of R.D. Alexander (Alexander, 1967; Alexander et al., 1963). In Russian an excellent review has been published by R.D. Zhantiyev (Zhantiyev, 1981) referring to where one more family of beetles producing sounds falseb powder-post beetles (Bostrichidae).
This page of our site is awaiting its author. Specialists from the Entomology Department of Moscow State University where the centre of the study of bioacoustics of insects in our country is situated promised to write about beetle sounds. Therefore I will only confine myself to making a few remarks.
The majority of beetles produce sounds by means of stridulation apparatus working by "comb and nail" principle. On one of the two rubbing surfaces there is a structure in the form of multiple parallel crests and on the other a denticle or one crest. When one surface moves in relation to another a sound resembling squeak arises. Stridulation apparatuses frequently occur in Cerambicidae. Saperda, a genus of cerambicids was called "squeakers" in Russian. It would be absolutely incorrect to apply that term to all representatives of the subfamily Lamiinae as it was recently done in one popular encyclopedia (Gornostayev, 1998). In cerambicids the stridulation area covered by thin ribs is situated in the anterior part of the mesonotum and is not seen in repose, because it is covered by pronotum. The sound arises when prothorax moves in relation to mesothorax, when the sharp posterior edge of the mesonotum glides across the stridulation area. When a cerambicid beetle is held by the abdomen and elytra it is clearly seen to produce squeak swinging the anterior part of its body up and down.
In some false powder-post beetles on the sides and prothorax rows of small knobs are situated and they produce sound by small "files" situated on the apices of profemora. For predacious diving beetles E.V. Shaverdo lists a number of structures that may be used for stridulation.
More rare in beetles is the pneumatic mechanism of making sounds produced by an abrupt release of air from the tracheal system through the abdominal stigmae. Such mode has been described for predacious diving beetles. E.V. Shaverdo assumes that the air blown out may vibrate lamella with transversal striation situated on the edges of the second sternite of the abdomen. In her essay on predacious diving beetles much more emphasis is placed on sounds than in descriptions of other families.
Representatives of several families produce sounds hitting their head or the end of the abdomen against substratum (the latter mode was repeatedly recorded for Tenebrionidae. Here one cannot but recollect the a href="tote_uhr.htm">"death clock" that is how many folks call some furniture or deadwatch beetles (Anobiidae) living in wooden articles and producing "sinister ticking". One of these species is the character of the narrative of S.S. Izhevsky, a guest of our site. Furniture beetles make sounds hitting head against walls of passages. Such way of communication is most probably aimed at facilitating of meeting of female and male for reproduction. However the purpose of sounds produced by larvae of Monochamus urussovi (Cerambycidae) deep in the wood of the trunk is unclear. The rate of their moving is so low that signals cannot help to meet. They are hardly needed to prevent such meeting - population density in one trunk is low and the probability of crossing of passages is negligible and poses no danger to diggers. The most interesting is that larvae inhabiting neighbouring trunks begin squeaking simultaneously, and it seems as if the sound is produced by the trees. Siberian entomologist Yu.N. Baranchikov (Krasnoyarsk Institute of Forestry, Russian Academy of Sciences) who informed me of this observartion has proposed an ingenious hypothesis of biological sense of this phenomenon. The sound produced by several larvae simultaneously vibrates in the trunk and disorientates their enemies (wood-peckers, :, and others). The sound goes from the entire trunk and it is very difficult to distinguish its separate sources.
The ability of click beetles (Elateridae) to produce a loud click, when a beetle lying on its back hops, is close to that of the percussion mechanism. This characteristic of (Elateridae) has been described many times and shown in figures. For a hop accompanied by a click a beetle hoops in such a way that the long process of prothorax protrudes from mesothoracic fossa and abuts against its edge. Then the beetle tautens, trying to bend and allows the process to come off and fall into the fossa. The body is jerked upwards the enemy may be frightened, not only by this sharp movement, but also by an unexpected sharp sound.
We can argue concerning the defence role of click in Elateridae, however the discharge of poisonous liquid in Carabidae: Brachininae is undoubtedly a weapon against enemies. An important constituent of this weapon is the sound. In our small Brachininae its strength and loudness are insignificant, but in large tropical species the sound is reminiscent of gun shot and may frighten even a large predator. In greater detail about this weapon you can read in the essay on ground beetles.
Physical characteristics of sounds produced by beetles are given in the above-mentioned review (Zhantiyev, 1981). The frequency is from 1 kiloherz (weevils and bark beetles) to 35 kiloherz (ultrasound in ground beetles of the genus Elaphrus. The level of sound pressure (loudness) in beetles is only 30-60 decibel, which is much lower than sound intensity of Auchenorrhyncha (up to 110-115 decibel).
The aforesaid shows that the modes of producing sound of beetles have been thoroughly studied. This is not the case with the auditory organs of beetles. The reason, to my mind, is that sound communication is not the main means of communication of beetles. Entomologists in the first turn try to study acoustic communication of Orthoptera, Auchenorrhyncha, some families of Lepidoptera and Heteroptera, i.e. those insect taxa for which producing and perception of sounds is of primary importance. Therefore the mechanisms of producing sounds that "lie on the surface" have been registered quite completely, and it is much more difficult to find information on the mechanisms of perception of sounds. I have succeeded to understand that sound fluctuations are perceived by Johnston's organs comprising modified chordonotal sensillae. The structure of auditory receptor of beetles is described in detail by the example of pond beetle Acilius sulcatus by Ivanov (1969).
The first original records of beetle sounds were made for our site by Svetlana Andreyeva.
A.L. Lobanov, August 2001 - September 2002
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