Black rugose trapdoor spider

Description

Idiosoma nigrum, also called black rugose trapdoor spider, occurs only in south-western Western Australia, in dry woodlands east of the Darling Scarp and north to Moore River. Females can reach a length of about 30mm, males about 18mm. Idiosoma nigrum digs burrows up to 32 cm deep. The species name is derived from Latin Niger "black". Idiosoma is a genus of Australian armored trapdoor spiders that was first described by Anton Ausserer in 1871. Originally placed with the Ctenizidae, it was moved to the armored trapdoor spiders in 1985. The name is derived from the Greek ἴδιος (idios), meaning "individual, unique", and σῶμα (soma), meaning "body", referring to the distinctive structure of the abdomen. The skin of their opisthosoma is hardened, with a flattened end and deep grooves running along the sides. The thickened skin helps to reduce water loss in its dry habitat. It also serves as a kind of plug to shield itself from predators. This phenomenon is called phragmosis and occurs in perfection in the spider genus Cyclocosmia (Ctenizidae). However, some parasitic wasps have evolved paper-thin abdomens and long, slender ovipositors and lay their eggs on the softer skin at the front of the spider's opisthosoma. It digs burrows up to 32 centimetres (13 in) deep, where the temperature is relatively constant during the seasons. When prey triggers any of the trip-lines radiating from the burrow's entrance, the spider runs out of the burrow to capture ants, beetles, cockroaches, millipedes and moths. This is unlike many trapdoor spiders that very rarely leave their burrow. Males actively look for females, and mating takes place in the female's burrow. She lays her eggs during late spring and early summer. The spiderlings hatch in mid-summer, and stay inside the burrow until early winter, when the climate gets more humid. The Black rugose trapdoor spider (Idiosoma nigrum) can grow up to 30 millimetres (1.2 in) long. Males can grow up to 18 millimetres (0.71 in) in body length.