Macracantha

Macracantha is a genus of Asian orb-weaver spiders recognized as containing a single species, Macracantha arcuata.[1] Macracantha is notable for the extremely long, curved spines on the abdomens of female members of the genus; Eugène Simon created the taxon name from the Greek words μακρός (large, long) and ἄκανθα (spine). It occurs from India and China through Southeast Asia to Borneo.[2]

Macracantha
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Araneidae
Genus: Macracantha
Simon, 1864[1]
Species:
M. arcuata
Binomial name
Macracantha arcuata
(Fabricius, 1793)[2]

Description

Female long-horned orb-weavers have tough, shell-like abdomens armed with three pairs of spines. The spectacular middle (median) spines project upward and outward, curving in toward each other along their length. They are up to three times as long (20-26 mm) as the abdomen is wide (8-9 mm). The front (anterior) and rear (posterior) spines are short, relatively inconspicuous, and roughly equal in length.[3][4]

The upper surface of the female abdomen ranges from yellow[4] to red[5] or even white or black[6] and is marked with black sigilla. The ventral surface of the abdomen bears yellow or orange marks, and the median spines can show a bluish iridescence.

The male of the species measures only 1.5 mm, with stout, conical spines.[7]

Taxonomy

The taxon was first described by Eugène Simon in 1864 as a subgenus of Gasteracantha,[8] and was raised to genus status in 1974 by Michel Emerit.[9]

M. arcuata was historically included in the genus Gasteracantha.[2] A 2019 study examining three mitochondrial and two nuclear genes found that M. arcuata is allied with Gasteracantha hasselti and Actinacantha globulata and that Gasteracantha is paraphyletic with respect to Macracantha, Actinacantha, and Thelacantha. The authors, however, did not propose generic reassignments based on their data.[10]

Possible additional species

On Borneo, where M. arcuata occurs, multiple observers have also photographed a colorful and dramatically shaped taxon that differs from typical M. arcuata in several respects:

  • longer, more strongly curved median spines;
  • different shape and arrangement of sigilla along the rear edge of the abdomen;
  • much longer posterior spines; and
  • consistently white dorsal surface of abdomen.[11][12][13][14] However, the World Spider Catalog lists only one species.[1]

Ecology

Female M. arcuata build orb webs three or four feet wide in forested areas. These webs have hollow hubs and white silk beads on the radial threads. Siliwal and Molur report that females were more often observed on the underside of leaves near their webs than hanging in the center of the web.[5][15]

In Singapore, the species depends heavily on primary rainforest.[16]

References
  1. "Gen. Macracantha Simon, 1864". World Spider Catalog. Natural History Museum Bern. Retrieved 25 August 2020.
  2. "Macracantha arcuata (Fabricius, 1793)". World Spider Catalog. Retrieved 25 August 2020.
  3. Tikader, B.K. (1982). The Fauna of India - Spiders: Araneae Vol. II. Calcutta: Zoological Survey of India. pp. 69–71.
  4. Pocock, R.I. (1900). The fauna of British India, including Ceylon and Burma. Arachnida. London: Taylor and Francis. p. 232.
  5. Molur, Sanjay; Daniel, B.A.; Siliwal, Manju (November 2004). "First record of Macracantha arcuata Fabricius, 1793 (Araneae: Araneidae) from Assam, India". Zoos' Print Journal. 19 (11): 1696. doi:10.11609/JoTT.ZPJ.1225.1696. Retrieved 3 August 2019.
  6. "Observations of Macracantha arcuata". iNaturalist. Retrieved 3 August 2019.
  7. Simon, E. (1903). "Etudes arachnologiques. 34e Mémoire. LIV. Arachnides recueillis à Sumatra par M. J. Bouchard". Annales de la Société Entomologique de France. 72: 301–302.
  8. Simon, E. (1864). Histoire naturelle des araignées (aranéides). Paris. p. 287. doi:10.5962/bhl.title.51973.
  9. Emerit, M. (1974). "Arachnides araignées Araneidae Gasteracanthinae". Faune Madagascar. 38: 29.
  10. Tan, Ji; Chan, Zi Yang; Ong, Ching Ang; Yong, Hoi Sen (14 February 2019). "Phylogenetic relationships of Actinacantha Simon, Gasteracantha Sundevall, Macracantha Hasselt and Thelacantha Simon spiny orb-weavers (Araneae: Araneidae) in Peninsular Malaysia". Raffles Bulletin of Zoology. 67: 32–55. doi:10.26107/RBZ-2019-0003.
  11. Bauer, Mikael. "Macracantha observed by neomorphus on March 25, 2015". iNaturalist. Retrieved 3 August 2019.
  12. Lee, Chien C. "Macracantha observed by cclborneo on June 3, 2010". iNaturalist. Retrieved 3 August 2019.
  13. Bay, Nicky. "Long horn orb weaver (Macracantha arcuata) - DSC_4787". Flickr. Retrieved 3 August 2019.
  14. Yeo, Melvyn. "Long horned Orb Weaver Spider". DeviantArt. Retrieved 3 August 2019.
  15. Siliwal, Manju; Molur, Sanjay (December 2005). "Some observations on the webs of Gasteracantha geminata (Fabricius, 1798) and Macracantha arcuata (Fabricius, 1793) (Araneae: Araneidae)". Zoos' Print Journal. 21 (1): 2133–2134. doi:10.11609/JoTT.ZPJ.1324.2133-4. Retrieved 3 August 2019.
  16. "Flora Fauna Web - Animal Detail - Macracantha arcuata (Fabricius, 1793)". NParks Flora&FaunaWeb. National Parks Board, Singapore. Retrieved 3 August 2019.
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