Spider tortoise (Pyxis arachnoides)

Description

Spider tortoise fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Spider tortoise description

The attractive spiders-web pattern that adorns the shell of this species is both the reason for its name and, owing to the exotic pet trade, one of the main factors behind its precarious situation ^{(1) (3) (5)}. The spider tortoise is a small reptile, with an oblong shell that is highly curved and widens towards the rear. The shell is decorated with five to eight yellow lines radiating out from a yellow centre, against a dark brown or black background. The shell on the underside of the tortoise, known as the plastron, is yellow. The head is dark and speckled with several yellow spots, and the legs and tail are brown. The tail of the male is longer and thicker than that of the female, and has a harder tip ⁽⁶⁾.

Three geographically separated subspecies of the spider tortoise are currently recognised (Pyxis arachnoides arachnoides, P. a. oblonga, and P. a. brygooi), with the presence, or varying mobility, of a plastron hinge providing the bases for this determination ^{(4) (7)}. Pyxis arachnoides arachnoides has a semi hinged plastron, allowing the tortoise to retract its head and front legs and close itself in its protective shell, hence the scientific name Pyxis, which means box. Pyxis arachnoides brygooi completely lacks a hinge on the plastron, while Pyxis arachnoides oblonga has the most mobile plastron hinge allowing complete closure and quite often has black marks on the plastron ⁽⁷⁾.

French

Pyxide Arachnoide, Tortue-araignée.

Spanish

Tortuga Araña.

Size

Average shell length: 11.1 ⁽²⁾

Spider tortoise biology

The spider tortoise is most active during the wet season ⁽⁹⁾, between November and April, when the vegetation is relatively lush, and the tortoise can feed on grasses, young leaves, the roots of succulents, and insects attracted to the flourishing plants. This tortoise is also known to feed on cow dung containing insect larvae ⁽¹⁰⁾. With the commencement of the dry season in April, many spider tortoises bury themselves deep into the sand and aestivate for the duration of the colder and drier weather, understood to be an energy and moisture-saving tactic for when vegetation is sparse ⁽⁹⁾. 

Fairly little is known about reproduction in the spider tortoise, but it is thought to mate at the beginning of the rainy season, resulting in a single egg being laid. In captivity, females laid three times a year; whether this reflects true behaviour in the wild is not clear. The eggs are incubated for between 220 and 250 days before tiny hatchlings, measuring just 4.5 centimetres long, emerge.  The young tortoises reach maturity at around 6 to 7 years, and are estimated to live for up to 70 years ⁽⁴⁾.

Spider tortoise range

The spider tortoise is endemic  to  the arid regions of the coastal areas of south-western Madagascar, where it is distributed from the coast up to about 20 kilometres inland ^{(2) (4)}. Historically the species inhabited a continuous strip of 555 kilometres of coastline from Morombe to the Amboasary region ⁽⁴⁾, however the range has become severely fragmented due to poaching and habitat destruction.The three subspecies are geographically divided across this range, with Pyxis arachnoides brygooi being the most northern subspecies, with three separate and fragmented populations, covering a total area of around 500 square kilometres of coastal forest ⁽²⁾. Pyxis arachnoides arachnoides has the largest and most geographically central range, while Pyxis arachnoides oblonga is  the most southern subspecies ⁽¹⁾. Like Pyxis arachnoides brygooi, the range of the more southerly subspecies is thought to be severely fragmented, but up to date, comprehensive distribution and range data has yet to be collected ⁽²⁾.

Spider tortoise habitat

This tortoise inhabits arid to semi-arid, Mikea Forests in the north and southern dry forests in the south. The habitat is typically comprised of sandy soil and low lying vegetation dominated by succulents and thorny shrubs ⁽⁴⁾. This species is dependent upon varying levels of canopy cover for thermal regulation, typically inhabiting areas of 30 to 50 percent canopy cover ⁽⁸⁾.

Spider tortoise status

Classified as Critically Endangered (CR) on the IUCN Red List ⁽¹⁾, listed on Appendix I of CITES ⁽³⁾ and and listed as Endangered under Malagasy National Law ⁽⁴⁾.

Spider tortoise threats

This species’ habitat has been seriously degraded, with an estimated 1.2 percent loss in habitat per year. The main causes of habitat loss and degradation in Madagascar include human-caused fires, conversion to agriculture, charcoal production, firewood exploitation and invasive alien plants ^{(1) (11)}. Madagascar’s burgeoning human population can only cause this problem to worsen ⁽¹¹⁾.

Compounding the threat of habitat loss is the impact of illegal harvesting for the international pet trade ⁽⁵⁾. The small size and attractive shell of the spider tortoise makes it an incredibly popular species in the pet trade. The order of 10,000 individuals in 2001 by one trader in the Comoros illustrates the massive demand for this species ⁽¹²⁾.   Despite the ban in international trade in the species under CITES, the animal is still thought to be being collected in vast numbers and smuggled out of Madagascar to support the pet trade, principally in Japan, Europe, North America and south east Asia ^{(5) (13)}. Spider tortoises are also harvested for local consumption, mainly towards the north of the range ⁽²⁾. Pyxis arachnoides brygooi is probably the most threatened subspecies and has vanished from over 50 percent of its historical range ⁽¹¹⁾.

Spider tortoise conservation

The Critically Endangered spider tortoise is protected by national law in Madagascar and listed on Appendix I of CITES, which prohibits international trade in this species. Unfortunately, compliance with the law is proving difficult to enforce, with large numbers leaving the country illegally to support the exotic pet trade ^{(4) (5)}, as well as being hunted for food by certain communities within Madagascar. The spider tortoise’s occurrence in two protected areas (Lake Tsimanampetsotsa National Park and Cap Sainte-Marie Special Reserve) offers some much needed protection, but owing to a lack of resources within the protected areas system, habitat destruction and poaching still continues ^{(4) (14)}. The need for a specific conservation action plan has been raised, in addition to stricter measures to protect its habitat, and the implementation of education programmes to try and protect this tortoise from hunting ⁽⁹⁾. These measures, in addition to ensuring that populations of all subspecies are represented within protected areas ^{(1) (15)}, are essential if the long-term survival of the spider tortoise is to be assured.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

For further information on conservation in Madagascar see:

• WWF:
  www.panda.org/about_wwf/where_we_work/africa/where/madagascar/index.cfm

• Wildlife Conservation Society:
  www.wcs.org/globalconservation/Africa/madagascar

Authentication

Glossary

Aestivate

To become dormant during the summer or dry season, analogous to hibernation in winter.

Endemic

A species can be described as Endemic to a particular country, region or habitat if it its occurrence is restricted exclusively to this particular country, region or habitat.

Larvae

Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.

Plastron

In reptiles, the lower shell of a turtle.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

References

1. IUCN Red List (November, 2009)
   http://www.iucnredlist.org
2. Walker, R.C.J. (2009) Preliminary results of a population range and density survey for Pyxis arachnoides brygooi in Madagascar. TurtleLog, 2. Available at:
   http://www.iucn-tftsg.org/turtlelog_online_newsletter/tln002
3. CITES (November, 2009)
   http://www.cites.org
4. Pedrono, M. (2008) The Tortoises and Turtles of Madagascar. Natural History Publications (Borneo), Kota Kinabalu, Malaysia.
5. Walker, R.C.J., Rix, C. and Woods-Ballard, A.J. (2004) The export of the endangered Madagascar spider tortoise (Pyxis arachnoides) to support the exotic pet trade. Herpetological Bulletin, 90: 2-9.
6. Bell, T. (1827) On two new genera of land tortoises. Transactions of the Linnean Society of London, 15: 392-401.
7. Chiari, Y., Thomas, M., Pedrono, M. and Veites, D.R. (2005) Preliminary data on genetic differentiation within the Madagascar spider tortoise, Pyxis arachnoides (Bell, 1827). Salamandra, 41: 35-43.
8. Walker, R.C.J. (2009) Pers. comm.
9. Walker, R.C.J., Woods-Ballard, A.J. and Rix, C.E. (2007) Population density and seasonal activity of the threatened Madagascar spider tortoise (Pyxis arachnoides arachnoides) of the southern dry forests; South West Madagascar. African Journal of Ecology, 46: 67 - 73.
10. Glaw, F. and Vences, M. (1994) A Field Guide to the Amphibians and Reptiles of Madagascar. Moos Druck, Leverkusen.
11. Harper, G.J., Steininger, M.K., Tucker, C.J., Juhn, D. and Hawkins, F. (2007) Fifty years of deforestation and forest fragmentation in Madagascar. Environmental Conservation, 34(4): 325-333.
12. CITES. (2002) Consideration of Proposals for Amendment of Appendices I and II, Proposal 15. Thirteenth Meeting of the Conference of the Parties, Bangkok, Thailand. Available at:
    http://www.cites.org/eng/cop/13/prop/index.shtml
13. Nijman, V. and Shepherd, C.R. (2007) Trade in non-native, CITES-listed, wildlife in Asia, as exemplified by the trade in freshwater turtles and tortoises (Chelonidae) in Thailand. Contributions to Zoology, 76(3): 207-212.
14. Behler, J. (2000) Letter from the IUCN Tortoise and Freshwater Turtle Specialist
    Group
     . Turtle and Tortoise Newsletter, 1: 4-5.
15. Mittermeier, R.A., Rhodin, A.G.J., Randriamahazo, H., Lewis, R.E., van Dijk, P.P., Hudson, R., and Rioux Paquette, S. (2008) Vision sokatra gasy - Madagascar turtle vision. Turtle and Tortoise Newsletter, 12: 7-9.