Poison sting (scorpions)

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Metasoma of an emperor scorpion with the membrane between the 4th and 5th segment ( A ), 5th segment ( B ), setae ( C ), anus ( D ), telson ( E ), poisonous bladder ( F ) and poisonous sting ( G )
Last segment of the metasoma, poisonous bladder with subacular tubercle and venomous sting with poisonous drops

The poison sting (also Aculeus, Latin aculeus , sting ' , plural: Aculei) of the scorpions is located on the last part of the body and forms the telson there together with the poisonous bladder . The telson and the comb organ are the most obvious distinguishing features of the scorpions compared to all other jaw-claw carriers . The poison sting is an important determinant of some taxa .

construction

Historical representation of the anatomy of the scorpions: poison sting from above ( 3 ) and from the side ( 4 ), each with marked outlet openings ( a , b ); Cross sections of the venomous spine at the base ( 7 ) and almost at the tip ( 8 ).

The poison sting is the outermost extension of the metasoma of the scorpions. It is demarcated from the poisonous bladder where the subacular tubercle, a small lump or spur at the end of the poisonous bladder, is located. The coloration, especially a sharp demarcation between the light attachment and the dark tip of the aculeus that deviates from the position of the subacular tubercle, is meaningless for the demarcation and for the determination of length.

The poison sting is part of the exoskeleton . In its interior, two channels run from the two poison glands in the poison bladder to two drop-shaped outlet openings that are only a few hundredths of a millimeter long and are located on the side almost at the tip of the poison spike. The canals appear under magnification with a bleached poisonous sting as tubes surrounded by thin membranes. When a sting occurs, a muscle contracts between the venom glands, and the scorpion venom is passed through the ducts from the venom glands to the tip of the venomous sting and pushed out. The shape of the outlet openings and their lateral position mean that they cannot be clogged by the body tissue of the opponent when stabbed. In addition, when the poison stinger is pulled out of a wound, the poison is not transported out with it.

For a long time the poison sting was only seen in its function as an instrument for injecting poison. In fact, it is a highly developed organ with different sensory capacities. The numerous long sensory hairs on the poisonous bladders of most scorpions and on the base of the poison sting are missing at the end. Instead, there are small cup-like depressions at the ends of the poison sting, in which there are short, club-shaped sensory hairs. The function has not yet been clarified with certainty; there are probably chemoreceptors at the bases of these sensory hairs . The sunk placement ensures that the poison sting can penetrate the body of an opponent with little resistance on the one hand, and that sensory perception is possible on the other. In addition, on the poison sting there are split sense organs , numerous pores, the meaning of which is unclear, and skin glands.

The scorpion's exoskeleton fluoresces under ultraviolet radiation . The distal part of the venomous sting is excluded . An explanation for this has not yet been found. In this area, however, a greatly increased concentration of zinc , manganese and iron was detected. Such deposits are also found in the chelicerae and the claws of the tarsi . In the mandibles of ants , it was found that such deposits increase the hardness of the mandibles threefold. It is possible that the metallic deposits in the poison spikes lead to reduced wear and tear and provide protection against breaking off.

use

The poison sting is both an instrument for catching prey and a weapon of defense against predators. However, there are clear differences in the frequency of its use among the approximately 2,000 species of scorpion. There are species that almost never use the poison sting, while others also kill small prey primarily with one sting. It is generally assumed that scorpions with relatively large, powerful chelae primarily use them for hunting and defense. Scorpios with poorly developed chelae are more likely to use the poison sting and have a stronger poison.

When the scorpions mate, the male scorpion stings the female in many species. The behavior is particularly common in species in the Chactidae family , but is not limited to them. The stitch is usually placed at the beginning of the "wedding dance", occasionally at a later point in time, in a membrane that is adjacent to the tibia of a pedipalpe . The sting then remains in the female's body from three minutes to more than 20 minutes. It is unclear whether poison is also deposited in the process. If that is the case, the function will be to calm the female. Further attempts at explanation indicate the possibility that when the male stings, chemical substances other than scorpion poison are deposited via the skin glands on the poison sting. Regarding the skin glands on the venomous spines of female scorpions, it has been speculated that they may release pheromones.

Some species of the genera Androctonus and Parabuthus make noise by scratching the surface of the mesosoma or metasoma with the poison sting . The Stridulation , for other types of scorpions different mechanisms have developed is probably deter predators .

evolution

Last segment of the metasoma , poisonous bladder and venomous sting of Gondwanascorpio emzantsiensis

Scorpions have in common with the pseudoscorpions the greatly enlarged pedipalps with the chelae at the ends. However, this is seen as a consequence of convergent evolution . The scorpions differ from all recent orders of arachnids by the telson with its two poison glands in the poison bladder and the poison sting as an exit, as well as by their comb organs . Accordingly, the scorpions of a clade from all other arachnids are added as a sister group.

The poison stings of the scorpions and other animal groups are not homologous .

Individual evidence

  1. ↑ Jean Joyeux-Laffuie: Appareil et venimeux venin du Scorpion . In: Archives de zoologie expérimentale et générale 1883, Volume 11, 733–783, Plate XXX, digitizedhttp: //vorlage_digitalisat.test/1%3D~GB%3D~IA%3Darchivesdezoolog2118laca~MDZ%3D%0A~SZ%3Dn843~ double-sided%3Dja~LT%3D~PUR%3D .
  2. ^ A b John T. Hjelle: Anatomy and Morphology. In: Gary A. Polis (Ed.): The biology of scorpions. Stanford University Press, Stanford 1990, pp. 9-63, ISBN 0-8047-1249-2
  3. ↑ W. David Sissom, Gary A. Polis and Dean D. Watt: Field and Laboratory Methods. In: Gary A. Polis (Ed.): The biology of scorpions. Stanford University Press, Stanford 1990, pp. 445-461, ISBN 0-8047-1249-2 .
  4. ↑ Thomas M. Root: Neurobiology . In: Gary A. Polis (Ed.): The biology of scorpions . Stanford University Press, Stanford 1990, pp. 341-413, ISBN 0-8047-1249-2 .
  5. ↑ a b c d Rainer Foelix, Bruno Erb and Matt Braunwalder: Fine structure of the stinger (aculeus) in Euscorpius . In: Journal of Arachnology 2014, Volume 42, No. 1, pp. 119-122, doi : 10.1636 / B13-64.1 .
  6. ^ Herbert L. Stahnke : The Genus Centruroides (Buthidae) and Its Venom . In: Sergio Bettini (Ed.): Arthropod Venoms (= Handbook of Experimental Pharmacology, Volume 48). Springer, Berlin, Heidelberg, New York 1978, pp. 277-307, ISBN 978-3-642-45503-2 .
  7. ↑ a b Sharon J. McCormick and Gary A. Polis : Prey, Predators, and Parasites. In: Gary A. Polis (Ed.): The biology of scorpions. Stanford University Press, Stanford 1990, pp. 294-320, ISBN 0-8047-1249-2 .
  8. ^ Gary A. Polis and W. David Sissom: Life History. In: Gary A. Polis (Ed.): The biology of scorpions. Stanford University Press, Stanford 1990, pp. 161-223, ISBN 0-8047-1249-2 .
  9. ↑ a b W. David Sissom: Systematics, biogeography, and paleontology. In: Gary A. Polis (Ed.): The biology of scorpions. Stanford University Press, Stanford 1990, pp. 64-160, ISBN 0-8047-1249-2