Drilus concolor

Drilus concolor
Drilus concolor ♂
Systematics
Order : Beetle (Coleoptera) Subordination : Polyphaga Family : Click beetles (Elateridae) Tribe : Snail shell beetle (Drilini) Genre : Drilus Type : Drilus concolor
Scientific name
Drilus concolor
Ahrens , 1812

Drilus concolor is a beetle from the family of beetles , and belongs to the tribe of the shell beetle . They used to form their own family. The genus Drilus is in Europe with fourteen species represented, of which, except in Central Europe Drilus concolor still Drilus flavescens occurs. As with all species in the family, only the male is built like a beetle, while the much larger female resembles a caterpillar .

The rare beetle is listed in the Red Lists of Saxony-Anhalt and Schleswig-Holstein in category 2 (endangered).

Notes on names and synonyms

The male of the beetle was described by Ahrens in 1812 under the name Drilus concolor . Ahrens remarks: Mr. Finance Secretary Zenker , to whom I sent this Beetle to be identified, gave it its name . The species name concolor ( Latin of the same color) is explained by the fact that in the male, in contrast to the Drilus flavescens described by Olivier in 1790 , the elytra are of the same color as the rest of the beetle. Olivier sets up the genre and also explains the name of the genus: …. under the name drile ( French ), from the Greek word δρίλος (Drilos), which was used by Hesychius to denote a type of insect or worm that is completely unknown to us (... sous le nom de drile, du mot grec δρίλος, employé par Hésychius, pour désigner quelque espèce d'insecte ou de ver, qui nous est entièrement inconnue). The assumption that the generic name refers to the larvae-like form of the female (Drīlus agr. Δρίλος drīlos, earthworm. - female larvae-like) is hardly true, since Olivier only describes the male.

Characteristics of the male

	Fig. 2: ♂ head from above
Fig. 1: ♂ different views	Fig. 3: ♂ Anterior tarsus
Fig. 4: antennae left ♂, middle ♀, right antennae phalanx ♀, a sensory process	Fig. 5: ♀ from above (right) and below (left)

The beetle is pale black, shiny, finely hairy and only slightly sclerotic . Its length is between four and five millimeters. The body shape is elongated and flattened and is somewhat reminiscent of the Dasytes genus .

The head is short and almost as wide as the pronotum . Behind the eyes it narrows a little. It is lowered slightly and sunk less deeply into the pronotum than in Drilus flavescens . It is indistinctly dotted . The forehead is broadly depressed between the eyes.

The eleven-jointed antennae (Fig. 4 left) are well twice as long as the pronotum. They are black and often lightened a little reddish at the base. The first antenna segment is strong, the next is short. The third antenna element is triangular, the following ones are built roughly the same and at the front inner corner widened in such a way that the antenna appears to be strongly sawn. The feelers are positioned on the side of the head in front of the eyes (Fig. 2). The upper lip is much wider than it is long and convexly narrowed on the sides, somewhat truncated in front, weakly edged and sparsely ciliated. The reddish, lightened, protruding upper jaws are narrow, slightly curved inwards and very pointed. A little above the center they have a tooth pointing inwards a little forwards (Fig. 2). The lower jaws do not have two, as usual, but only one ark, which is relatively small. The four-part jaw probes are a little longer and slightly stronger than the three-part lip probes. The base link of the jaw probe is small, the following two links only slightly larger and cylindrical. The end link is elongated egg-shaped, pointed at the end. The first two links of the lip switch are cylindrical and almost identical in shape. The distal phalanx is significantly longer and oblong ovoid. The parchment-like tongue is short.

The pronotum is about one and a half times as wide as it is long and irregularly square. It is only slightly narrower than the wing-coverts, narrower behind than in the middle, the sides are slightly convex. The side edge is slightly bent up, the back corners rectangular to obtuse. The pronotum is flat and slightly uneven. The dots are indistinct and wrinkled.

The label is triangular to ovoid.

The elytra are about five times as long as the pronotum. They are only slightly rounded outwards at the sides, but individually rounded at the rear. They are indistinctly dotted. The points partially converge laterally and give the wing covers a pitted appearance.

The underside (Fig. 1 top right) is also black, glossy and dotted. The legs are quite short, the rails compressed. The narrow tarsi are five-limbed, the first four limbs are roughly the same, the claw limb is longer (Fig. 3), the claws are strongly curved. The tarsi are brown-black.

Characteristics of the female

In 1824 a female Drilus was not recognized as such and described as a new insect species, but in the same year this assessment was contradicted and the animal was classified as a female of Drilus flavescens . In 1870 Carl v. Heyden a Drilus larva in the shells of the snail Cepaea nemoralis , the larva developed into a female. Since Carl v. Heyden found males of the species Drilus concolor at the same time , but not of Drilus flavescens , he assumed that he had a female of this species. He characterized the female as smaller and darker than the female of Drilus flavescens , the pronotum as less transverse, the antennae as more rounded and not narrowed towards the base. In 1909, Rosenberg described and photographed the females he had bred from larvae (Fig. 5).

The females are about three times the size of the males and grow up to fourteen millimeters long. They are very short and dense yellow-brown, almost bristly hairy, wingless and larva or caterpillar-shaped. They are widest halfway along. They are almost uniformly red-brown, because the dark brown horizontal stripes on the tergites are not interrupted in the middle as in Drilus flavescens , which results in variable dark spots in the latter. The body consists of twelve segments. The last segment is much narrower than the previous ones and has two coarse, hairy, pen-like, movable appendages. The eleven-link antennae (Fig. 4 center) are short and like a string of pearls. The second limb is almost as long as it is wide, while in Drilus flavevens it is almost twice as long as it is wide. The last antenna segment has a pin-shaped sensory process (in Fig. 4, greatly enlarged on the right, marked with a). The upper jaw is only slightly bent inwards, the inner tooth is relatively small and blunt. The pronotum has two small pits at the base. The legs are protruding to the side. The tarsi are slender, the terminal segment longer than the rest of the segments together.

Larvae, pupa

Fig. 6: penultimate larval stage, ♀ summer form	Fig. 7: Last larval stage, ♀, resting stage left from top right underside

The species shows hypermetamorphosis during development . There are two different types of larvae, a summer form and a winter form. The first larval stages belong to the agile summer form. These larvae (Fig. 6) are very agile animals with functional legs, antennae and mouthparts. The flat head points forward. It is heavily sclerotized, a third wider than it is long, and sunk somewhat into the prothorax. There is a pinhole ( ocellus ) on each side of the head . The antennae are four-part, the sensory receptors are on the penultimate part. The base element of the sensor is very soft and allows the three remaining sensor elements to be placed backwards in a recess on the side. This prevents the antennae from being smeared with mucus when the larva sinks its head deep into the victim's body. The mouthparts are directed forward. The head shield is slightly curved in front and finely haired. The crescent-shaped mandibles are toothless and have a tubular canal. The jaw probes are four-part, the lip probes are two-part. The laterally directed legs are five-limbed. On each side of the abdomen, there are two superimposed and slightly rearward-facing processes. These are still very weakly developed in the first segment, stronger in the following two sections and very strongly developed and long hairy from the fifth to the eighth segment. On the ninth abdominal segment, there are two backward-facing, strong and warty appendages ( urogomphi ), which are also very hairy. Since the chest and abdomen are also hairy, the larva is protected by thick fur. Outgrowths and hairs are still relatively short in the early larval stages, but increasingly long in the later stages. The fur protects the animal from the breathing holes being smeared with snail slime. In addition, the inside of the eaten snail shells is cleaned with the help of the hair. The spiracles lie on the first to eighth abdomen segment between the dorsal and lateral outgrowths and are clearly recognizable. The anal segment is converted into an organ that the larva can use to suck in ( pygopodium ).

The last larval stage usually overwinters and sheds its skin in spring to form a pupa. This winter form (Fig. 7) has stunted legs and mouthparts, the antennae, lateral body appendages and urogomphi are only vaguely developed. The larva is maggot-like and pale. It is blind, almost hairless, and the stigmas are microscopic. The head is only slightly sclerotized. Since it takes two to three years to develop, the larva hibernates once or twice before that. For this, too, a molt takes place, which leads to an inactive winter form. This type of larva can also appear in the summer, for example after consuming a particularly rich prey. That is why the winter form is also known as the resting stage.

The larvae of the males are smaller and slimmer than the female larvae of the same age.

The pupa of the females already looks very similar to these. The shape of the male can already be seen in the much smaller pupa of the males.

biology

The adult beetles can be found from May to June on moist meadows or on river and lake banks, while the warmth- loving Drilus flavescens prefers dry slopes. The males are lazy fliers and can be found on low bushes. The females live hidden between grass and under moss and only present themselves when they are ready to mate. They then climb lower plants. Since the females are wingless, the possibility of spreading is very limited.

The larvae feed exclusively on shell snails. They climb onto an inhabited snail shell and examine it for suitable size. If the shells are too large or too small, they look for alternatives until they have found a suitable snail shell. Then suck on it with the pygopodium and bite into the victim from above, preferably into the antennae. In doing so, they pump a toxic digestive fluid into the body of the prey via the pointed, hollow mandibles. They continue their attacks until the snail is weakened. Then they crawl into the shell next to the snail. Or the gripped larva can be pulled into the housing when the snail retreats for protection. The snail finally succumbs to the bite and is digested and sucked up by the larva outside of the digestive tract (extratestinal) under the protection of the shell. This takes about two weeks. The larva is then always found stretched out with its back on the spindle of the snail shell and with its abdomen towards the mouth. In the course of the summer, several snails are eaten by the larva, and each time after the snail is eaten, it also sheds its skin in the shell after another three to four weeks. In autumn, the second larval type moults. The winter larva is also initially in the position just described. In the course of this inactive stage, however, the larva turns so that its head is in the direction of the mouth of the snail shell and the belly points towards the helix. The stripped larval skin is pushed towards the mouth and closes it protectively.

The larvae are fully grown in the second or third autumn. The last larval stage overwinters and pupates in the snail in spring. The pupa develops into an imago within approximately three weeks. The imago does not strip off the pupal shell when molting, but remains in it until its exoskeleton is fully hardened. The adults appear at the end of May. Females who show themselves are usually harassed after just a few minutes by several males, who in turn fight each other violently. It can be assumed that the males are attracted by a fragrance. For Drilus flavescens a putrid, musty scent that disappears after copulation has been documented. The copula takes about half an hour. Rüschkamp describes the oviposition of Drilus flavescens very precisely . In this type, the eggs are placed next to each other very carefully, the appropriate position for each egg is felt with the fallopian tube and a geometric figure (halved retorde) is generated. Deubel reports that a female from Drilus concolor laid the eggs in two lumps. The eggs are laid soon after copulation. Multiple mating were also observed.

It takes two or three years to develop. The males die soon after mating, the females soon after oviposition.

distribution

The species is widespread in large parts of Europe and is also reported from the Caucasus . According to Fauna Europa, it is absent in Western Europe and large parts of Southern Europe. However, there are more recent reports from France ( Lorraine ). Data from Lithuania are also not taken into account .
Within Germany, the species can be found especially in the hilly part of the south and the middle. To the west it becomes rare, especially in the lowlands.

literature

• Heinz Joy, Karl Wilhelm Harde, Gustav Adolf Lohse: The beetles of Central Europe . tape 6 : Diversicornia . Spectrum, Heidelberg 1979, ISBN 3-87263-027-X . P. 52
• Klaus Koch : The Beetles of Central Europe Ecology . 1st edition. tape 2 . Goecke & Evers, Krefeld 1989, ISBN 3-87263-040-7 . P. 42
• Wolfgang Willner: Pocket dictionary of the beetles of Central Europe . 1st edition. Quelle & Meyer, Wiebelsheim 2013, ISBN 978-3-494-01451-7 . P. 226
• Edmund Reitter : Fauna Germanica, the beetles of the German Empire III. Volume, KGLutz 'Verlag, Stuttgart 1911 p. 253
• Adolf Horion : Beetle science for nature lovers . Vittorio Klostermann, Frankfurt am Main 1949

Individual evidence

1. ↑ Drilus concolor in Fauna Europaea. Retrieved April 28, 2015
2. ↑ Drilus at Fauna Europaea. Retrieved April 28, 2015
3. ↑ Red List of Saxony-Anhalt - Weichkäfer, p. 289
4. ↑ Red list of beetle species endangered in Schleswig-Holstein, p. 41
5. ↑ Sigmund Schenkling: Explanation of the scientific beetle names (species)
6. ↑ ^{a b} M. Olivier: Entomologie ou Histoire naturelle des Insectes Coléoptères, Volume 2 Paris 1790 No. 23 .
7. ↑ Sigmund Schenkling: Explanation of the scientific beetle names (genus) in detail in the 2nd edition 1922.
8. ↑ ^{a b c d} EC Rosenberg: "Bitrag til Kundskaben om Billernes Udvikling, Levevis og Systematik, II. Drilus concolor Ahr .: Hunnens Forwandling i Skallen af Helix hortensis " in Entomologiske Meddelelser Volume 8, 3rd Vol, 4th Issue 1909 p 227 Danish text , French summary , illustrations
9. ↑ August Ahrens: Contributions to the knowledge of German beetles in Neue Schriften der Naturforschenden Gesellschaft zu Halle 2nd volume, issue 2, Hall 1812 2nd volume, issue 2 p. 13 in the Google book search
10. ^ Ludwig Redtenbacher: Fauna Austriaca - Die Käfer 3rd edition, 2nd volume, Vienna 1874 p. 18
11. ↑ WF Erichson et al .: Natural history of the insects of Germany Coleoptera fourth volume Berlin 1857 p.567
12. ↑ Drilus at coleo-net
13. ^ ^{A b} Adolf Horion : Beetle science for nature lovers . Vittorio Klostermann, Frankfurt am Main 1949 p. 107
14. ↑ Bernhard Klausnitzer: Wonderful world of the beetles . Herder Verlag Freiburg ISBN 3-451-19630-1 p. 113
15. ↑ Viktor Hansen: Danmarks Fauna - Biller Copenhagen 1938 p. 207
16. ↑ ^{a b c} Friedrich Deubel: "The development of Drilus concolor Ahr." in negotiations and communications of the Transylvanian Society for Natural Sciences in Sibiu, Volume 63, year 1913, Sibiu 1913, p.58 .
17. ↑ ^{a b} E. Rüschkamp: On the biology of the Drilidae and Micromalthidae in Biologisches Zentralblatt Volume 40, Issue 8/9 Leipzig 1920 p. 378
18. ↑ Polish coleopterological page on Art
19. ↑ Distribution map of the FE, accessed on May 8, 2015 ( Memento of the original from May 18, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
20. ↑ Find in Lorraine ( Memento of the original dated May 6, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
21. ↑ Occurrence in Lithuania
22. ↑ Adolf Horion : Faunistics of the Central European Beetles Vol. V, Tutzing 1956

Web links

Commons : Drilus concolor  - album with pictures, videos and audio files