Soft beetle

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Soft beetle
Red soft beetle (Rhagonycha fulva)

Red soft beetle ( Rhagonycha fulva )

Systematics
Class : Insects (Insecta)
Order : Beetle (Coleoptera)
Subordination : Polyphaga
Partial order : Elateriformia
Superfamily : Elateroidea
Family : Soft beetle
Scientific name
Cantharidae
Imhoff , 1856
Common soft beetle ( Cantharis fusca ) mating
a species of the genus Chauliognathus
a species of the genus Malthinus
Silis percomis in Michigan, USA
Rhagonycha nigriceps in Genoa, Italy
Species of the genus Trypherus in which you can see the shortened wings.
Athemus suturellus
Variable soft beetle ( Cantharis livida ), video (1m 53s)

The soft beetles (Cantharidae) are a family of beetles (Coleoptera) that are distributed worldwide. Delkeskamp's current list of species dates back to 1977 and 1978. It includes 137 genera and 5083 species . Countless other genera and species have been added since then, but the family remains little researched and many species have not yet been described. In Europe they occur with 530 species and subspecies, of which 103 species in 9 genera are also found in Central Europe . They got their German name because of their weakly sclerotized bodies. They are also called soldier beetles because many species are strikingly red, black, yellow or blue in color.

features

Beetle

The beetles are 1.2 to 28 millimeters long. Their body is elongated, has more or less parallel side edges and is moderately flattened. They have a soft body, in which the cuticle, especially wing covers (elytra) and abdomen only weakly sclerotized and is flexible. Their coloration is very variable and ranges from completely black to predominantly red, orange or yellow. More rarely they are colored metallic blue or green. Warning colors are particularly pronounced on the pronotum and / or the upper wings, whereby these areas are often two-colored, spotted or bordered. The body is usually more or less inconspicuous, moderately dense and short, with flat-fitting flowers. Less often the animals have sparsely longer, almost upright setae on the wings.

The head is at least partially visible from above. It is directed strongly forwards (prognath) or somewhat downwards; it is rarely hypognathic. In some species it is constricted directly behind the eyes. The compound eyes are more or less entire and somewhat protruding. In the males they are often larger, in most ichthyurini they are greatly enlarged. Point eyes ( Ocelli ) are missing. The frontoclypeal suture is usually absent, only in the Chauliognathini it is laterally developed. With the exception of this tribe, the labrum is fused with the frontal plate ( clypeus ) or frontoclypeus. In the case of the Chauliognathini, on the other hand, it can be partially or completely divided in the middle. The antennae are elongated and have 11 links. As a rule, they are thread-like, sometimes toothed, only rarely pinnate, fanned, club-shaped, thickened or differently developed between the sexes and / or differently modified in the males. The mandibles are more or less elongated, curved and have a pointed tip. They are usually simple, sometimes with one or more teeth on the inner edge. The maxilla has densely hairy stores ( Galea and Lacinia ), the latter is regressed or absent in some species. The maxillary palps are four-membered. The labium has an undivided ligula. The labial palps are tripartite.

The pronotum is usually almost square to transverse. It is seldom narrowly elongated. The sides are edged, with the margins usually being whole, sometimes somewhat to greatly expanded. The sides of the males of some species are heavily sculpted, notched or provided with pits. The posterior margin of the pronotum is either as wide or narrower than the base of the wing base. The scutellum is well developed and visible. The legs are usually elongated and slender. In some species the thighs ( femora ) of the middle legs are greatly enlarged. With the exception of the Chauliognathini, there are paired spurs on the rails ( tibia ). All three pairs of legs each have five tarsus links . The fourth phalanx is enlarged and doubly lobed ventrally . The soft wings (Elytren) are usually more or less parallel-edged. They are seldom widened at the tip. They are only loosely connected to the pterothorax and abdomen. In a number of species they are severely to completely regressed, whereby several abdominal gites and / or the hind wings are visible. The hind wings are usually well developed.

The abdomen in the females and some males has seven, in most of the other males eight freely movable ventrites (visible abdominal sclerites ). The first eight tergites have glandular pores arranged in pairs. In many Silini, evertable glands are formed laterally in the intersegmental membranes. The last or last abdominal segments are often modified.

Larvae

The larvae have an elongated body, the side edges of which are more or less parallel. Your cuticle is densely covered with the finest folds that give it a velvety appearance. The surface of the body is almost always covered with very short, upright hairs. The body is at least partially darkly pigmented, sometimes with spots in pairs, most often on the back. The head is strongly directed forward. A single, large point eye ( stemma ) is located on both sides of the head and is rarely missing. The labrum is fused with the head capsule and forms a clypeolabrum. The antennae are tripartite. The second link is trimmed and has the area with the sensory hairs at the end (Cantharinae, Silini, Chauliognathini), or the second link is strongly notched and has an elongated, subapical sensory field. The mandibles are sickle-shaped and have a more or less well-developed longitudinal canal that is usually wide open, but sometimes almost closed. The maxillary palps are three or four, the labial palps two-part.

The thorax segments are almost the same size or become increasingly smaller towards the rear. All terga of the thorax and the first eight tergites of the abdomen have glandular pores. In some species, these are also formed on the ninth segment. The legs are five-limbed, the pretarsus is claw-shaped and carries four or more setae. The abdomen segments are almost the same length at the front, and they are shorter at the back. Urogomphi are absent.

Occurrence

The soft beetles are distributed all over the world, but their main distribution is in the tropics of Asia and South America. However, the family also makes up a large part of the beetle's biodiversity in the temperate regions. In America north of Mexico it is the 13th most species-rich beetle family. Soft beetles are very numerous, especially in forests. However, there are also species that inhabit grasslands, savannas and montane meadows. Many species are apparently adapted to forest clearings, edge habitats or succession areas. In hotter habitats, they tend to live close to bodies of water.

Way of life

The animals live terrestrially in all life stages. They spend most of their life during the larval stage, during which most species live in association with the soil. They can be found in microhabitats with high relative humidity, such as in or under dead leaves, in the litter of forests, under stones, in loose soil or under loose bark of dead wood. The larvae of species of the genus Chauliognathus have a conspicuous warning look , they eat clearly visible in the open. The surface of the cuticle is hydrophobic in the larvae , which means that they are better protected against flooding in their habitats. In the vast majority of species, the larvae feed on liquid food as predators. They use their hollow mandibles and a filter as well as a special pump-like pocket in the oral cavity to soak up the liquid. The prey animals include various invertebrates such as earthworms (Lumbricidae), snails (Gastropoda) and the eggs, larvae and imagines of other insects. Some species can even take on dangerous predators such as the larvae of the tiger beetle (Cicindelinae). Under laboratory conditions, cannibalism has also been demonstrated in overpopulations. In addition to the purely predatory species, there are also those that omnivorously eat plant material.

The larval development can be very complex and include up to 10 larval stages. In some species the antennae, mouthparts and legs have regressed in the first stages and do not ingest food. Pupation usually takes place in a chamber in the ground. In the temperate latitudes, the animals form one generation per year, overwinter as larva and hatch in spring or early summer as imago. The adult beetles only live for a few weeks and are very active. They can be found on almost any type of living vegetation. They colonize a huge variety of different plant species, from conifers to flowering herbaceous plants. However, some species prefer certain types of plants. The beetles of the genus Chauliognathus z. B. can often be observed when visiting flowers and are important pollinators of these plants. The adults of many species are good fliers and actively fly while foraging for food or on the run from predators. Most species appear to be diurnal, although some are attracted by artificial light sources at night. The adult beetles feed on invertebrates they find on foliage or eat nectar or pollen. In many species of the Podabrini and Cantharini , they feed primarily on tube aphids (Aphididae), but also on nectar. Like the larvae, they also ingest nutritious fluids. It is known of the genus Chauliognathus that the adults only eat pollen and nectar. However, the feeding behavior of many other groups of soft beetles is unknown.

Larvae and adults have glandular pores arranged in pairs on the sides, which they use to secrete foul-tasting substances. Many species, especially adults, warn potential predators of these with their warning colors . There are also a number of species that have developed mimicry , imitating not only species of various other beetle families, but also bedbugs, two-winged birds and butterflies. The interaction of all these defense mechanisms has enabled the soft beetles to establish themselves very successfully, despite their poorly armored body.

The males of some species have unusual secondary sexual characteristics, such as antennae modified in grasping devices, notched and specially shaped lateral edges of the pronotum and the tips of the wings, or elaborately modified abdominal ends. All of these are useful for the animals when mating and make it easier to recognize the species. The secretion of pheromones also plays an important role in mating behavior. In some genera the antennae of the males have elongated flagellate branches that enlarge the sensory surface and thus facilitate the detection of pheromones.

Taxonomy and systematics

The relationship of the soft beetles is still unclear. In the course of the research history, their taxonomic position to other beetle families changed several times. Among other things, they were also placed in their own superfamily Cantharoidea. However, this superfamily was dissolved again and the groups included were added to the Elateroidea , which is now considered a more likely hypothesis. However, the relationship within this superfamily is unclear.

The larvae of the family can easily be recognized by their velvety body surface. The most important synapomorphies of the soft beetles are the glandular pores, which are formed in both the larvae and the adults. These are located on the tergites of the first to eighth abdominal segments of the imagines and on all terga of the thorax and the first eight (or nine) abdominal segments of the larvae. The family monophyly is well established by these characteristics. For most of the subfamilies and tribe (such as the Cantharini, Silini and Dysmorphocerinae) there are no identification keys for identification at the genus level. The possibility of identifying species of weicb beetle depends primarily on their geographical distribution. For Canada, Korea, Japan, New Guinea , Northern Europe, Oceania, Russia, Taiwan, and the United States, with a few exceptions, there is sufficient literature to make a determination. In the case of many genera, however, a reliable determination is only possible by examining the male genitals.

The following subfamilies and tribes are distinguished:

with distribution on the land masses of the former Laurasia :

also with distribution indicated in brackets:

Fossil Finds

The oldest soft beetle found to date comes from the late Cretaceous and is 116 million years old and was found in Victoria, Australia near Koonwarra . This temporal classification is also supported by the disjoint distribution of the subfamily Dysmorphocerinae (southern Africa, South America, New Zealand, Australia and New Guinea) and the tribe Chauliognathini (North and South America, Australia and New Guinea), which suggests a historical vicariance .

Types (selection)

supporting documents

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p Richard AB Leschen, Rolf G. Beutel, John F. Lawrence: Handbuch der Zoologie - Coleoptera, Beetles, Volume 2: Morphology and Systematics (Elateroidea, Bostrichiformia, Cucujiformia partim) . de Gruyter, 2010, ISBN 978-3-11-019075-5 , p. 153 ff . (English).
  2. ↑ Cantharidae. Fauna Europaea, accessed March 28, 2013 .
  3. ^ A b Karl Wilhelm Harde , František Severa : Der Kosmos-Käferführer. The Central European beetle . Franckh-Kosmos, Stuttgart 2000, ISBN 3-440-06959-1 , p. 182 f .

literature

  • Richard AB Leschen, Rolf G. Beutel, John F. Lawrence: Handbuch der Zoologie - Coleoptera, Beetles, Volume 2: Morphology and Systematics (Elateroidea, Bostrichiformia, Cucujiformia partim) . de Gruyter, 2010, ISBN 978-3-11-019075-5 (English).

Web links

Commons : Soft Beetle  - Collection of images, videos and audio files