Flat-bellied spiders

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Flat-bellied spiders
Heathen night hunter (Haplodrassus signifer), female

Heathen night hunter ( Haplodrassus signifer ), female

Systematics
Sub-stem : Jawbearers (Chelicerata)
Class : Arachnids (arachnida)
Order : Spiders (Araneae)
Subordination : Real spiders (Araneomorphae)
Superfamily : Gnaphosoidea
Family : Flat-bellied spiders
Scientific name
Gnaphosidae
Pocock , 1898

The flat-bellied spiders (Gnaphosidae, Syn . : Drassodidae, Prodidomidae, Drassidae), sometimes also called smooth- bellied spiders , form a family within the order of the spiders . Apart from their characteristic optical appearance, the species of this family, which is almost worldwide, are characterized by their way of hunting (see section “ Hunting behavior and catching prey ”).

features

Males of the common iris spider ( Micaria pulicaria ), one of the more conspicuously colored species of the family.

The flat-bellied spiders are small to very large with a body length of two to 18 millimeters and have a strong body. Their body is flattened and mostly covered with velvety hair. There are both dark and low-contrast types, but also some colorful types. An example of this are the Schiller spiders ( Micaria ).

Basic physique

Female flat-bellied spider with clearly recognizable physique including petiolus

The general body structure of the flat-bellied spiders is divided, as with all spiders, into the two body regions of the prosoma (front body) and the opisthosoma (rear body), both of which are connected by the petiolus . Occasionally, individual characteristics of the body regions can help to identify the species (especially genital morphological characteristics).

Prosoma

Scheme of a female of Latreille's black spider ( Zelotes latreillei ) including the position of the eyes and the ventral view of the area between the labium and the chelicerae , detail from The Common Spiders of the United States by Ginn & Company. Boston. (1902).

The carapace (back shield of the prosoma or front body) is egg-shaped, fairly low and also smoothly convex in the flat-bellied spiders. Many species have a very pronounced fovea (apodem). The head is not sharply separated from the rest of the prosoma.

Flat-bellied spiders, like most spiders, have eight eyes, which in the species in this family are not very efficient and are divided into two rows. The posterior medial eyes are often not round, but oval, triangular or reduced to slits. Apart from the front and darker central eyes, the eyes of the flat-bellied spiders have a silvery sheen.

The chelicerae (jaw claws) of the flat-bellied spiders are robustly built and also toothed. On the retromarginal side of some species there may also be a sclerotized (harder) layer, which then shows the teeth. The sternum (breast shield of the prosoma) of the representatives of the family is egg-shaped and elongated backwards.

In particular, the curvature of the posterior row of eyes, the shape of the labium (lip) and the teeth of the chelicerae are often important features to distinguish similar genera of flat-bellied spiders from one another.

extremities

Frontal detail of a prepared male of Sergiolus capulatus with clearly visible leg hair.

The legs of the flat-bellied spider are stocky and all of the same length and in some species are lighter in color on the distal or proximal side than the rest of the body.

A characteristic feature of the species of the family are the two claws provided with tufts of hair on the tarsi (foot members) and the presence of a and scopula (hairiness of the tarsi ). In some types of flat-bellied spiders there are small brushes with more and less stiff hair, which are then present on the distal side of the metatarsi of the fourth pair of legs.

The pedipalps (transformed extremities in the head area) of the flat-bellied spiders are provided with small spines and a finely toothed claw.

Opisthosoma

Spinnerets of Herpyllus ecclesiasticus

The opisthosoma (abdomen) of the flat-bellied spiders is not infrequently provided with short and smooth hair. In some species there are also curved hairs, especially on the front edge of this body section. The hairiness, together with its silhouette, gives the opisthosoma, viewed from the dorsal side, an appearance that is reminiscent of that of a mouse . This has also given the genus the mouse spider ( Scotophaeus ) its common name .

A striking feature of the flat-bellied spiders are the cylindrical spinnerets , which in the rest position are either arranged parallel to one another or spread apart like fingers and at an angle. The spinnerets, which are arranged parallel to one another in the rest position, are very mobile. The spinnerets of the flat-bellied spiders have no cribellum or calamistrum , which makes the representatives of this family ecribellate spiders . In most species, the males have a scutum (sclerotized or hardened area) near the spinning tower .

In many members of the family, the opisthosoma is uniformly gray-brown or blackish in color and has no sign elements. In other representatives, however, there are often conspicuous white patterns of spots or lines and again in other species the opisthosoma shimmers, for example through iridescence (light breakage ).

Genital organs

Photomicrograph of a single globe (the top three graphics) and the epigyne of Pterotricha strandi

As with other spiders, individual representatives of the flat-bellied spiders have species-specific genital morphological features, which in some genera of the family is the only reliable way to differentiate individual species. The sexual organs of all types of flat-bellied spiders have the following characteristics:

The bulbi (male sexual organs) of the flat-bellied spiders are provided with a large and depending on the species differently shaped tibia apophysis ( chitinized area), while the mostly quite large epigyne (female sexual organ) has sclerotized structures and sections.

Confusion of flat-bellied spiders with sac spiders

Female of the pale bag spider ( Cluiona pallidula ) from the family of the bag spiders (Clubionidae)

Individual species of flat-bellied spiders can be confused with those of the closely related family of sack spiders (Clubionidae). The flat-bellied spiders differ from these, however, in the shape of their rear eyes and in particular in the structure of their spinnerets. These are conical in the sack spiders tapering to the rear and not one-piece and appear cylindrical or somewhat flattened.

Occurrence

Distribution map of the smooth-bellied spiders

The flat-bellied spider family is found almost all over the world. Only in the Arctic , the Antarctic and the south of Argentina and Chile are there no species of the family.

Habitats

Many flat-bellied spiders inhabit dry, warm and open habitats, such as limestone lawns .

The preferred habitats of flat-bellied spiders can vary greatly depending on the species. However, most species are ground-dwelling and prefer dry and warm as well as open habitats. Still others are partially or even entirely synanthropic (preferring human settlement areas), including the lesser mouse spider ( Scotophaeus blackwalli ) in the northern parts of their range.

Threat and protection

The small flat-bellied spider ( Gnaphosa opaca ) is one of the endangered species of the family

As with many spider families, the different types of flat-bellied spiders have different levels of risk. While the populations of adaptable and / or widespread species have not declined dramatically, the opposite is true for other species that are more closely linked to specific habitats, which is often associated with the decline in these habitats. This can be observed particularly strongly in the case of the flat-bellied Rhine spider ( Gnaphosa rhenana ), which is listed in the Red List of Endangered Species of Animals, Plants and Fungi in Germany in Category 1 ("threatened with extinction").

Way of life

Residential web of a flat-bellied spider

The representatives of the flat-bellied spiders are apparently mainly nocturnal apart from the more contrasting colored species. During the day, these species can be found in tubular webs under stones or leaves. The diurnal species do this accordingly at night. Almost all flat-bellied spiders cannot make safety and orientation threads.

Flat-bellied spiders orient themselves in and analyze their environment with the help of tactile stimuli. To do this, they have trichobothria (whiskers) on their legs, which register air movements, while other sensory organs are used to perceive ground vibrations. The sense of sight, however, is not of great importance, not even for the diurnal representatives of the family.

Hunting behavior and catch of prey

Flat-bellied spider looking for prey at night

The species belonging to the family of flat-bellied spiders, like many members of the Dionycha group, do not create nets , but hunt freely as hunters . The hunt takes place in the activity time of the species, which varies depending on the species.

Ways of hunting

Small mouse spider ( Scotophaeus blackwalli ) with prey

The flat-bellied spiders have different hunting strategies, depending on the size and defensiveness of the respective prey. Like the environment, these are perceived through the trichobothria and the perception of vibrations. The procedure for killing a prey depends on its size and ability to fight.

Smaller or less defensive prey animals are simply grabbed with the legs and immediately afterwards put out of action with a poisonous bite injected with the help of the chelicerae . If a prey turns out to be too big or more defensible for a direct attack, the hunter provides it with a spider thread after jumping , which the spider attaches to both the prey and the ground. The spider then feeds and moves away from the prey several times while it produces more threads, so that the prey is prevented from fleeing and the restricted freedom of movement prevents adequate resistance. If it is adequately secured, the spider finally incapacitates it with a poison bite and then consumes it.

Loot spectrum

The common ant thief ( Callilepis nocturna ) is one of the family's food specialists ; it only preyed on ants.

Flat-bellied spiders can, due to their successful trapping method, also overwhelm prey that significantly exceed their own body dimensions. Many species are opportunistic hunters and feed on any arthropod. However, this family also includes food specialists who specialize in killing certain prey. Examples of this are the species of the ant thief genus ( Callilepis ) and those of the Nomisia genus , whose species have specialized in capturing ants.

Reproduction

Schematic of a female flat-bellied spider making cocoons , laying eggs and fertilizing the eggs

The mating behavior of the flat-bellied spiders is largely unexplored. In most species, the female guards its mostly paper-like egg cocoon until the young spiders hatch, hidden in its web of dwelling or in small holes, e.g. B. tree trunks or stones.

Systematics

The World Spider Catalog lists 161 genera and 2546 species including subspecies for flat-bellied spiders . This makes them the seventh largest spider family.

Description history

The family of flat-bellied spiders has been changed and renamed several times. In addition, more genera and subfamilies were outsourced to other families, including those of the sac spiders (Clubionidae), those of the bark sac spiders (Corinnidae) and that of the ant sac spiders (Phrurolithidae). Individual taxa were also increasingly incorporated into the family of the smooth-bellied spider, and some made into subfamilies that were once regarded as independent families of the order of the spider web.

Descriptive history of the Prodidomidae

For the first time in 1833 a family of the Drassidae was first described by Carl Jakob Sundevall , which today is considered a synonym of the family of flat-bellied spiders, first described by Reginald Innes Pocock in 1898 . The family of the Prodidomidae , which was first described by Eugène Simon in 1884 and has since been downgraded, including the subfamilies of the Prodidominae , the Molycriinae and the Anagraphidinae , was revalidated in 1990 by Norman Ira Platnick , and in 2006 the subfamily of the Anagraphidinae was reclassified to the Glattbauchsp under Barbara C. Baehr and Platnicksp . In 2018, the entire family of the Prodidomidae was dissolved by Guilherme HF Azevedo , Charles Edward Griswold and dalberto José dos Santos and the remaining subfamilies were also placed under the family of flat-bellied spiders.

Controversial and unclear affiliation of various taxa

The taxonomic affiliation of the genus of Schiller spiders ( Micaria ), the monotype type Nauhea tapa and the genus Verita to the family of ground spider are controversial today. In addition, some genera of the family cannot be assigned to a secure subfamily due to insufficient knowledge.

Genera of the family

The following genera belong to the flat-bellied spider family:

No longer recognized genera

Two genera within the flat-bellied spider family are now considered the nomina dubia . These genera are as follows:

  • Melicymnis Simon , 1885
  • Theumella Beach , 1906

Genera never recognized

Apart from the two no longer valid genera and there are three others that were never recognized after their first description and are therefore considered to be nouns nuda . These genera are:

  • Iyoa Brignoli , 1983
  • Joshidaia Brignoli , 1983
  • Oenosomum Brignoli , 1983

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q Gnaphosidae (Pocock, 1898) from The Spiders of Europe and Greenland, accessed on July 21, 2020.
  2. ^ A b Stefan Heimer, Wolfgang Nentwig: Spinnen Mitteleuropas. Verlag Paul Parey, Berlin 1991, ISBN 3-489-53534-0 .
  3. ↑ a b c d e f g h Gnaphosidae (Pocock, 1898) in the Wiki der Arachnologische Gesellschaft e. V., accessed on July 21, 2020.
  4. ↑ a b c d Heiko Bellmann: The cosmos spider guide. Over 400 species in Europe. Kosmos Naturführer, Kosmos (Franckh-Kosmos), 2nd edition, 2016, p. 242, ISBN 978-3-440-14895-2 .
  5. ↑ Araneae (Clerck, 1757) at the Red List Center, accessed on July 21, 2020.
  6. ↑ a b J. O. Wolff, M. Řezáč, T. Krejčí, SN Gorb: Hunting with sticky tape: functional shift in silk glands of araneophagous ground spiders (Gnaphosidae) , Journal of Experimental Biology, Volume 220, 2017, pp. 2250-2259 , accessed on July 21, 2020.
  7. ↑ Link Gnaphosidae (Pocock, 1898) at Spiders of NW-Europe, accessed on July 21, 2020.
  8. ↑ a b c d e f Natural History Museum of the Burgergemeinde Bern: World Spider Catalog Version 19.5 - Gnaphosidae . Retrieved December 16, 2019.

literature

Web links

Commons : Flat-bellied Spiders  - Collection of images, videos and audio files