Madagascan Spider Tortoise

The spider tortoise is most active during the wet months of the rainy season (5), when the vegetation is relatively lush, and the tortoise can feed on grasses (2), young leaves (1), the roots of succulents, and insects attracted to the flourishing plants (2). This tortoise is also known to feed on cow dung containing insect larvae (1). 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-saving tactic for when vegetation is sparse (2) (5). Fairly little is known about reproduction in the spider tortoise (1), but it is thought to mate at the beginning of the rainy season, resulting in a single egg being laid (2). In captivity, females laid three times a year; whether this reflects true behaviour in the wild is not clear (2). The eggs are incubated for between 220 and 250 days before tiny hatchlings, measuring just 4.5 centimetres long, emerge (2). The young tortoises reach maturity in two years (2), and are estimated to live for up to 70 years (1).

Under law, the Critically Endangered spider tortoise is fairly well protected. It is a protected species in Madagascar, which prohibits its consumption (2), and its listing on Appendix I of the Convention on International Trade in Endangered Species (CITES) is supposed to prohibit any international commercial trade in this species (3). The spider tortoise's occurrence in two protected areas (Lake Tsimanampetsotsa National Park and Cap Sainte-Marie Special Reserve) also offers its habitat some much needed protection (1) (2). The need for a specific conservation action plan has been raised, in addition to stricter measures to protect its habitat and education programmes to try and protect this tortoise from hunting (1). These measures, in addition to ensuring that populations of all subspecies are represented within protected areas (1), are essential if the long-term survival of the spider tortoise is to be assured.

The attractive spiders-web pattern that adorns the shell of this species is both the reason for its name, and one of the factors behind its now precarious situation (1) (2). The spider tortoise is a small reptile, with an oblong shell that is highly curved and widens towards the rear (2). The shell is decorated with five to eight yellow lines radiating out from a yellow centre, against a dark brown or black background (2). 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 (2), and males and females can also be distinguished by the generally larger size of the females (4). Three subspecies of the spider tortoise are recognised. Pyxis arachnoides arachnoids has a hinged plastron, which allows the tortoise to close itself in its protective shell; the scientific name arises from this feature, as Pyxis means box in Greek. Pyxis arachnoides brygooi is the smallest subspecies and lacks a hinge on the plastron, while Pyxis arachnoides oblonga has, as its names suggests, the most oblong shell, and has black marks on the yellow plastron (2).

This tortoise inhabits arid to semi-arid areas, typically in areas of sandy soil and where the vegetation is dominated by succulents and thorny shrubs (2). It is sometimes found among sand dunes near the sea, where there is very little vegetation (2).

The spider tortoise is found only in the arid regions of the coastal areas of south-western Madagascar, where it is distributed from the coast to between 10 and 50 kilometres inland (1). The three subspecies occupy different parts of this range, with Pyxis arachnoides brygooi being the most northern subspecies, Pyxis arachnoides arachnoids occupying the central part of the range, and Pyxis arachnoides oblonga being the most southern subspecies (1).

Classified as Critically Endangered (CR) on the IUCN Red List (1) and listed on Appendix I of CITES (3).

The habitat in which the spider tortoise exists has been seriously degraded. Human-caused fires, conversion to agriculture, charcoal production, firewood exploitation and invasive alien plants have all taken their toll on the habitat and reduced the distribution of the spider tortoise (1) (2). It is of great concern that with Madagascar's burgeoning human population, this habitat destruction can only worsen (2). Compounding the threat of habitat loss is the impact of harvesting for the international pet trade (1) (2). 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 (2). Collection for the pet trade has increased in recent years, and is becoming more of a serious problem (2). A small number are also harvested for local consumption, but the impact of this on the species is nominal in comparison to the threats of habitat loss and international trade (2). Pyxis arachnoides brygooi is considered to be the most threatened subspecies, which has vanished from some areas and is declining in others (1).

Continent: Indian-Ocean
Distribution: Madagascar (along the S coast from the Mahajamba River southward around Cape Sainte-Marie almost to Fort-Dauphin)
Type locality: Unknown; designated as "Soalara (Baie de Saint-Augustin), sud-ouest de Madagascar" by Bour 1978:153.

The spider tortoise (Pyxis arachnoides) is a species of tortoise in the family Testudinidae that is endemic to Madagascar and is one of only two species in the genus Pyxis.