Tarsus (arthropod)

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Insect leg: The multi-part tarsus is the last section

The Tarsus (Greek neulateinisch; plural usually Tarsen , rare Tarsi ) is called the foot distal (last) section of the leg of the arthropods .


Tarsal limbs

Tarsus of the hind leg of a wood beetle ( Tillus elongatus )
Tarsus of a leaf beetle : the pair of claws is easy to see

Especially in the case of insects , the tarsus consists of several members (a maximum of five), which are of particular importance as recognition and identification features. The first, often enlarged, phalanx is called the heel peg or metatarsus. The formation of the tarsal limbs can vary greatly according to the respective way of life.

The tarsi formula indicates how many members the tarsi of the front, middle and rear legs consist of. For example, the tarsi formula 5-4-4 says that the tarsi are five-limbed on the front legs, but the tarsi on the middle and rear pair of legs only consist of four limbs.

The tarsal limbs often have appendages that support adhesion to smooth surfaces. Often several tarsal links have pillow-shaped projections on the underside, the euplantulae. In many species of beetles, the underside of some or all of the tarsal links is covered with a thick felt felt. Sometimes some of the tarsi links are also widened for even better adhesion.

Praetarsus and Appendices

Insect tarsus with appendages of all four species:
1 claw / claw
2 pulvillus
3 empodium
4 arolium

The pretarsus (sometimes also called post-tarsus ) sits on the last phalanx as a separate structure . However, it only consists of a clearly identifiable segment in rock jumpers (Archaeognatha) and Sackkieflern (Entognatha). Usually it is reduced to a membranous remnant and several small sclerites . Therefore, often only its appendices are recognizable from the Praetarsus.

On the pretarsus there are one or two claws , which are also known as claws or in Latin unguis (plural Ungues ). They sit dorsal to the last phalanx. In some groups there is also a hook-shaped sclerite between them, which simulates a third claw. The claws articulate on a sclerotized process of the last segment of the tarsus, called the unguifer.

In different orders of insects there are additional attachments on the pretarsus, which serve as adhesive pads on smooth surfaces. An unpaired, lobe-like extension with a smooth surface is called an arolium . Paired, lobe-like appendages attached to the base of the claws are called pulvillae . Another process called the empodium may sit between the pulvillae ; this can be bristle-like or lobe-shaped. A lobed empodium can be distinguished from the arolium by its fine structure. These extensions sometimes occur in combination with one another (see figure on the left).

be crazy

Many spiders have an adhesive pad called a scopula on the underside of the tarsi . The pads , which consist of thousands of tiny hairs, convey adhesive forces that enable the spiders to find support on smooth surfaces. In contrast to insects, no liquid is excreted for better adhesion. The adhesive pads are therefore more similar to the gecko's adhesive organs , which also provide adhesion when dry. The assumption that larger spiders, especially tarantulas, can also produce spider silk within these adhesive pads on the tarsi was refuted again in 2012 by researchers at the Neue Kantonsschule Aarau and the University of Cambridge .

See also


  • RG Beutel, SN Gorb: Ultrastructure of attachment specializations of hexapods (Arthropoda): evolutionary patterns inferred from a revised ordinal phylogeny. In: Journal of Zoological Systematics and Evolutionary Research. 39, 2001, pp. 177-207.

Individual evidence

  1. See Duden online: Tarsus
  2. The Praetarsus of the insects ( Memento of August 29, 2008 in the Internet Archive ) Construction of the Praetarsus
  3. ^ Drawing from Francis Walker (1851): Insecta Britannica: Diptera . Volume 1, p. 332.
  4. ^ Rainer F. Foelix, Bastian Rast, Anne M. Peattie: Silk secretion from tarantula feet revisited: alleged spigots are probably chemoreceptors. In: The Journal of Experimental Biology. 215, 2012, pp. 1084-1089. doi: 10.1242 / jeb.066811