Field cricket

Field cricket
Female field cricket ( Gryllus campestris )
Systematics
Class : Insects (Insecta) Order : Grasshoppers (Orthoptera) Subordination : Long- probe horror (Ensifera) Family : Real crickets (Gryllidae) Genre : Gryllus Type : Field cricket
Scientific name
Gryllus campestris
Linnaeus , 1758

The field cricket ( Gryllus campestris ) is a species from the family of the real crickets (Gryllidae) within the order of the locusts (Orthoptera). It was 2003 , the insect of the year in Germany, and in 2014 the animal of the year in Switzerland.

features

Male crickets are 19 to 23 mm long, females reach 17 to 22 mm and whose rearwardly projecting ovipositor (ovipositor) additionally reaches even a length of 8 mm to 12th This type of cricket is glossy black to, more rarely, brown in color and has a stocky, cylindrical shape with strong legs. The head is spherical and has powerful biting tools, about 20 mm long, thin antennae and three bright point eyes (ocelli) on the forehead; the prothorax is rectangular when viewed from above. The brownish to deep black, at the base yellow fore wings are well developed and hardened to Tegmina . They have black veins and are used by males for stridulation . The forewings are morphologically divided into a dorsal field and a lateral field. The dorsal field lies horizontally over the abdomen, the lateral field is almost perpendicular to it and partially covers the side of the abdomen. Most descriptions do not distinguish between the two parts. Information about the forewing mostly only refers to the dorsal field. As with all crickets, the dorsal part of the right fore wing lies above the left, the wings almost completely covering the abdomen . The brownish hind wings, on the other hand, are stunted and only reach two thirds of the abdominal length, only with the variation ( Gryllus campestris var. Caudata ) they are fully developed. This variation occurs more frequently in southern European populations , but very rarely in central Europe. Caudal to the abdomen are two cerci (abdominal appendages). The hind legs are reddish ventrally (on the stomach). A large and a small eardrum are formed in each of the front rails . They are used to hear and locate rivals in the neighborhood.

The field crickets jump relatively rarely and then only short distances. But they are nimble runners. However , the field cricket cannot normally fly clumsily, like its Mediterranean sister species Gryllus bimaculatus . Only the variation ( Gryllus campestris var. Caudata ) is able to do this.

Occurrence

The Feldgrille loves warm, sunny and dry slopes, meadows, gravel pits and heaths, as well as light pine forests . The animals dig 10 to 20 cm deep and about 2 cm wide tubes in the earth, also called 30 to 40 cm deep tubes. The species is found from North Africa across Central and Southern Europe to the Caucasus. In the coastal regions of southern Europe it occurs together with the Mediterranean field cricket . The field cricket is more common in southern Germany than in northern Germany.

nutrition

The field cricket is omnivorous, but mainly consumes vegetable food. Larvae and adults feed on leaves and roots of various plants and herbs. But they also eat small soil animals and their carcasses .

Stridulation and acoustic communication

Play media file

Stridulating male

The Feldgrille has a highly developed acoustic communication that is based on differentiated sound and auditory organs. Only the sexually mature males are able to utter vocalizations, which are called singing, chirping or stridulation, the process of sound formation accordingly as singing, chirping or stridulation.

Stridulation organ

Stridulating field crickets

To generate sound, the males use the dorsal fields of the forewings, which have specialized structures that occupy almost the entire dorsal field. This includes the shrill loader that starts from the base of the wing, initially pulls backwards like the other large veins and then turns to the inner edge of the wing after a short course. From approximately the arch to almost the end of the vein, the underside is covered with teeth arranged in a row, the shrill teeth or lamellae. The part of the shrill vein covered with teeth forms the shrill bar. The field cricket has an average length of 4.35 mm and an average of 138 shrill teeth made of chitin and specially shaped. In the middle section of the grooved edge, the distance between the grooved teeth is 40 µm and decreases to 25–30 µm towards the two ends. Next to the end of the shrill vein, a small, thickened and pigmented section protrudes at the edge of the wing, the shrill edge. Following the shrill loaders, there are structures on the wing that serve to amplify the sounds. The harp or diagonal field is the part of the wing through which some wavy veins run, followed by the mirror, a large, approximately round field that is crossed by a vein. The end section of the wing (apical field) is traversed by a network of small and irregular veins.

Both grand pianos are equipped with a complete and identically built singing set. For a long time it was believed that the male crickets use either one of the two shrill strips and the shrill edge of the other wing to stridulate. This is not the case, as investigations with the Mediterranean field cricket have shown (see there). Since the right wing is always above the left, the shrill strip of the right wing strokes the shrill edge of the left wing when the sound is generated. To stridulate, the males lift both forewings 45–60 °, spread them slightly to the side and then move them rhythmically against each other.

The lure song has two intensity maxima, a narrow maximum at 4-5 kHz and a broad one at 10-16 kHz. The harp has the greatest importance for the emission of sound. After removing the harps on both grand pianos, the sound pressure level decreased by an average of 46 dB. The removal of the mirror cells affected the broad maximum at 10-16 kHz. After separating the lateral fields, the sound pressure level of both maxima decreased, that of the narrow one by 8–15 dB. If the experimentally removed harps and lateral fields were replaced by 5 µm thin PVC foils (“prostheses”), the sound level increased again, but did not reach the normal value. These results obtained with the field cricket also apply to Gryllus bimaculatus and Acheta domesticus .

Female crickets cannot stridulate because they have no sound-making facilities. Their forewings have an even pattern of small diamonds.

Chants

The field cricket has several forms of singing with biological meaning: ordinary or enticing singing, rival singing and advertising singing.

Lure singing: The lure singing can be heard most often, which the males usually emit with great perseverance at the entrance to their cave, with their heads turned inwards. The males chirp when they have formed a sperm-filled spermatophore and are ready to mate. The singing can be heard about 50–200 m away. It consists of units of three to six, usually four, rapidly succeeding syllables, separated by intervals. The males are acoustically active from May to the end of June or into July. The daytime activity depends primarily on the outside temperature. On sunny and warm days, the singing can be heard from late morning until late at night. The animals become particularly active shortly before a heat thunderstorm.

Rival song: If two males meet while wandering in the area, they feel each other with their feelers and soon afterwards deal with these blows. Finally, the territory owner begins with the rival song, which consists of a long sequence of similar sound signals. The intruder usually gives way to this. Otherwise it can lead to very violent, even fatal, fighting.

Commercial singing: Commercial singing in front of a female is relatively quiet. It consists of short impulses that are emitted in an irregular sequence and with different volume. The stridulation movements of the wings are correspondingly irregular.

Hearing organ

The pair of auditory organs ( tympanic organs ) are located in the rails ( tibia ) of the front legs. Each organ has two eardrums of different sizes, which can be recognized from the outside because they are not sunk into pits. The eardrums are used to record sound and locate relevant sound sources. Inside, the leg trachea lies against the eardrums, with which about 40 sensory cells are connected, which are arranged in a row and form the hearing bar. Their dissipating fibers represent the auditory or tympanic nerves.

pairing

Nymph from above; easily recognizable by the not yet fully developed wings

To mate, a female migrates from a distance of up to 10 m towards a singing male. The immigration takes place in a zigzag line, but the main direction is towards the male. The female also finds the male in tall and dense grass. If this interrupts its song, the female remains or wanders around undirected until the male continues the lure song. Once the female has reached the male, it is followed by touching with the feelers, then the male begins to sing and turns the end of his body towards the female. When mating, the female rises from behind on the male, who then bends his abdomen upwards and mates with the female. It fixes the 2.3 mm long, pear-shaped spermatophore (sperm carrier) in the genital opening of the female in about a minute. After the female has dismounted, the male performs a so-called Nachbalz for one to two hours, making jerky movements accompanied by antenna tremors. The female starts laying eggs three to four days after mating. With the help of its laying tube, it buries the eggs one by one in the earth. In the course of life, a female cricket lays several hundred eggs.

As early as 1913, J. Regen demonstrated in an experiment that the males' lure song serves to attract females ready to mate. With a microphone, he registered the enticing song of a male and played it over a telephone receiver in another room in which a female was. The female ran towards the telephone receiver, suspecting a male there.

development

The larvae hatch two to three weeks after the eggs are laid. They stay together for some time and initially live above ground under stones, in earth tubes or in other hiding places. They moult several times until they separate in autumn and dig in individually. In April of the following year, when the soil warms up again, the larvae shed their skin for the tenth or eleventh time to become imago and become sexually mature.

Hazard and protection

Increasing loss of habitat, mostly due to intensive agriculture, means that cricket populations are declining in many regions. In some areas they are already extinct. They are classified as 3 (endangered) in the Red List of the Federal Republic of Germany.

swell

Individual evidence

1. ↑ The IUCN Red List of Threatened Species 2017-2: Gryllus campestris
2. ↑ ^{a b c} Anna Alfonsa Stark: Investigations on the sound organ of some crickets and grasshopper species, at the same time a contribution to the right-left problem. In: Zoological Yearbook. Department of Anatomy and Ontogeny of Animals. 77, 1958, pp. 9-50.
3. ↑ ^{a b c} Harald Nocke: Biophysics of sound generation by the front wings of the crickets. In: Journal of Comparative Physiology . 74, 1974, pp. 272-314.
4. ^ Bertrand & Hannes Baur, Christian & Daniel Roesti: The locusts of Switzerland. Haupt Verlag, Bern 2006, ISBN 3-258-07053-9 .
5. ↑ J. Regen: About the attraction of the female of Gryllus campestris L. by the male's stridulation sounds transmitted by telephone. In: Pflüger's archive. 155, 1913, pp. 193-200.
6. ↑ Federal Agency for Nature Conservation (Ed.): Red List of Endangered Animals in Germany. Landwirtschaftsverlag, Münster 1998, ISBN 3-89624-110-9 .

literature

• Max Beier, Franz Heikertinger: Grilling and mole crickets . (= Die Neue Brehm-Bücherei. Issue 119). A. Ziemsen Verlag, Wittenberg Lutherstadt 1954.
• Anna Alfonsa Stark: Investigations on the sound organ of some crickets and grasshopper species, at the same time a contribution to the right-left problem. In: Zoologisches Jahrbuch, Department for Anatomy and Ontogeny of Animals. 77, 1958, pp. 9-50.
• Harald Nocke: Biophysics of sound generation by the front wings of the crickets. In: Journal of Comparative Physiology . 74, 1974, pp. 272-314.
• J. Regen: About the attraction of the female of Gryllus campestris L. by stridulation sounds of the male transmitted by telephone. In: Pflüger's archive. 155, 1913, pp. 193-200.
• Gunnar Höpstein: The field cricket - a secret insect. 2003.
• Werner Kriechbaum: Time structure of the lure song in Gryllus campestris L. 1983.
• Thomas J. Langner: Gryllus campestris Linnaeus, 1758, Feldgrille. 2004.
• H. Reichholf-Riehm, G. Steinbach, R. Kühbandner: Insects. (= Steinbach's nature guide. Volume 7). Bertelsmann & Mosaik, Gütersloh / Munich 1984, ISBN 3-570-01187-9 .
• Christian Venne, Frank Ahnfeldt: Resettlement of the field cricket (Gryllus campestris) in Bielefeld? 2003.

Web links

Commons : Feldgrille  - album with pictures, videos and audio files

• Chirps and photo
• Egg laying - film on Youtube
• Gryllus campestris at Orthoptera.ch
• Species photos of Gryllus campestris in the species finder