Triangular Spiders - Family: Arkyidae
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Arkyids or Triangular Spiders are a small family of 38 species in two genera. Many are oddly shaped, relying on camouflage and/or mimicry to avoid the attention of their predators. Others are brightly coloured with triangular or heart-shaped abdomens. The family was described in 1872 by Christian Koch and placed as a a subfamily of the Araneidae. There it remained until 2017 when Dimitrov et al. published a paper that argued for its' elevation to family status. Of the two genera, Arkys is the larger and its' species are predominantly Australian with some also occuring in New Guinea, Indonesia and a few in New Caledonia. The six species in the Genus: Demadiana are exclusively Australian.
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The Family: Arkyidae is family of fairly small spiders with body length not often exceeding 8 or 9 mm. The front two pairs of legs of some members of the Genus: Arkys usually are considerably larger than the rear two pairs and they are held two by two in a sweeping forward arch. There are also a few species that are not as bold in their appearance and they may resemble bird-droppings or blotches on a leaf. All of these spiders may be found in open eucalypt woodlands and forests but, being ambush hunters, they do have a tendency to hide during the day. At night they may seen hanging on to a silk line or two suspended from the foliage. They do not build webs.
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Their prey consists of insects smaller than themselves which they catch with their enlarged forelegs. Their use of silk is restricted to egg casings and to set lines between leaves or twigs for movement between parts of the plant or, to suspend themselves from waiting for prey. Eyesight in the Arkyidae is not considered to be good due to the small size of the eyes.
At the end of summer, the females builds a little egg sac into which she places some 50-odd eggs. The egg sac is about 7 mm long and is suspended from a stalk. The Genus: Demadiana contains six species of small spiders with short legs and a bulbous abdomen that is triangular only when viewed from above. They are not often seen. |
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Winged Arkys - Arkys alatus
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High-headed Arkys - Arkys alticephala
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Arkys bulburinensis
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Horned Arkys - Arkys cornutus
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Bird-dropping Arkys - Arkys curtulus
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Dilated Arkys - Arkys dilatatus
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Arkys enigma (possible occurrence)
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Fork-tailed Arkys - Arkys furcatus
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Arkys gracilis (possible occurrence)
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Common Triangular Spider - Arkys lancearius
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Arkys latissimus (possible occurrence)
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Arkys multituberculatus
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Arkys semicirculatus (possible occurrence)
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Speechleyi's Arkys - Arkys speechleyi
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Arkys transversus
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Knobbly Arkys - Arkys tuberculatus
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Walckenaer's Studded Triangular Spider - Arkys walckenaeri
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Dermadiana carrai (possible occurrence)
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Taxonomy:
Phylum: Arthropoda (Arthropods)
> Subphylum: Chelicerata (Chelicerates)
> Class: Arachnida (Arachnids)
> Order: Aranea (Spiders)
> Suborder: Araneomorphae (Typical Spiders)
> Infraorder: Entelegynea (Entelegyne Spiders)
> Superfamily: Araneoidea (Araneoid Spiders)
> Family: Arkyidea (Triangular Spiders)
> Genus: Arkys
> Species: A. alatus - Winged Arkys
> Species: A. alticephala - High-headed Arkys
> Species: A. bulburinensis
> Species: A. cornutus - Horned Arkys
> Species: A. curtulus - Bird-dropping Arkys
> Species: A. dilatatus - Dilated Arkys
> Species: A. enigma ^
> Species: A. furcatus - Fork-tailed Arkys
> Species: A. gracilis ^
> Species: A. lancearius - Common Triangular Spider
> Species: A. latissimus ^
> Species: A. multituberculatus
> Species: A. semicirculatus ^
> Species: A. speechleyii - Speechleyi's Arkys
> Species: A. transversus
> Species: A. tuberculatus - Knobbly Arkys
> Species: A. walckenaeri - Walckenaer's Studded Triangular Spider
> Genus: Demadiana
> Species: D. carrai ^
* = likely
^ = possibly
References and links:
> Balogh, P., (1982). 'Some new Archemorus species (Araneidae).' Acta Zoologica Hungarica 28: 15-21.
> Dimitrov, D., Benavides, L.R., Arnedo, M.A., Giribet, G., Griswold, C.E., Scharff, N. and Hormiga, G., (2017). 'Rounding up the usual suspects: a standard target-gene approach for resolving the interfamilial phylogenetic relationships of ecribellate orb-weaving spiders with a new family-rank classification (Araneae, Araneoidea).' Cladistics 33(3): 221-250 & Suppl. doi:10.1111/cla.12165
> Framenau, V.W., Scharff, N. and Harvey, M.S., (2010). 'Systematics of the Australian orb-weaving spider genus Demadiana with comments on the generic classification of the Arkyinae (Araneae: Araneidae).' Invertebrate Systematics 24(2): 139-171. doi:10.1071/IS10005
https://australian.museum/learn/animals/spiders/triangular-spiders-arkys-spp/
http://www.brisbaneinsects.com/brisbane_orbweavers/TriangularSpider2.htm
> Balogh, P., (1982). 'Some new Archemorus species (Araneidae).' Acta Zoologica Hungarica 28: 15-21.
> Dimitrov, D., Benavides, L.R., Arnedo, M.A., Giribet, G., Griswold, C.E., Scharff, N. and Hormiga, G., (2017). 'Rounding up the usual suspects: a standard target-gene approach for resolving the interfamilial phylogenetic relationships of ecribellate orb-weaving spiders with a new family-rank classification (Araneae, Araneoidea).' Cladistics 33(3): 221-250 & Suppl. doi:10.1111/cla.12165
> Framenau, V.W., Scharff, N. and Harvey, M.S., (2010). 'Systematics of the Australian orb-weaving spider genus Demadiana with comments on the generic classification of the Arkyinae (Araneae: Araneidae).' Invertebrate Systematics 24(2): 139-171. doi:10.1071/IS10005
https://australian.museum/learn/animals/spiders/triangular-spiders-arkys-spp/
http://www.brisbaneinsects.com/brisbane_orbweavers/TriangularSpider2.htm
Photographic contributions: