Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
Order Amblypygi

Common names: whip spiders, whip scorpions

Overview

Amblypygi are moderate to large spider-like arachnids which are commonly referred to as whip spiders or tail-less whip scorpions. They are usually less than 50 mm long and can be extremely flattened. Like spiders, the body is divided into two sections by a medial constriction or pedicel. However, they differ from spiders in many ways, the most striking being the enlarged and raptorial (talon-like) pedipalps which are armed with variably developed spines. Another unique feature is their highly modified antenna-like first pair of legs, in which the terminal portion comprises many (more than 100) small segments. These legs function as tactile sensors and one is usually extended in the direction the animal is moving. Amblypygi usually walk in a sideways or crab-like manner and are capable of extremely fast movement. The abdomen is segmented and possesses clearly defined tergites and sternites, and attaches to the prosoma via a narrow pedicel, similar to spiders. Despite their fearsome and spider-like appearance, whip spiders are not dangerous to humans and do not possess venom

Distribution and diversity

Australian whip scorpions have been found in rainforest or cave habitats in Arnhem Land, Christmas Island, and from Cape York Peninsula to south of Townsville. They are one of the smaller arachnid orders with about 140 species globally and only four described species from two genera in two families in Australia.

Life cycle

Amblypygi mate following a series of ritualised movements (mostly by the male) that include tapping the female with the elongate first legs, grasping the female with the pedipalps, and rocking back and forth. The male eventually produces a spermatophore (sperm packet), and guides the female over it using his pedipalps and/or first legs, until the spermatophore is taken up into her gonopore (genital opening). Eggs are laid into a membranous brood sac and remain attached underneath the female�s abdomen until they hatch. The juveniles crawl onto the abdomen of their mother and remain with there until their first moult, the time at which they become independent. Sexual maturity is attained after a series of moults.

Feeding

Amblypygi are ambush predators and they capture small invertebrates (mostly insects) with their raptorial pedipalps. Prey is carefully guided towards the pedipalps with the antenniform legs while the rest of the body remains motionless. When in range, the pedipalps rapidly grab the prey and force it into the chelicerae, where it is torn apart. Like most other arachnids, whip spiders do not ingest solid food, but rather prey is partially digested pre-orally before the liquefied contents are consumed.

Ecology

Most whip spiders are tropical and their flattened bodies are adapted for living under rocks and sheets of bark. Their impact as predators on invertebrate populations is unknown and they are not considered commercially significant.