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What are arachnids?

Arachnids include spiders, scorpions, harvestmen, mites and ticks. Their body is made up of two parts called the cephalothorax and abdomen. They have eight legs. 

Arachnids also have a pair of chelicerae which are mouthparts that are used for catching and holding prey and a set of pedipalps which look like another pair of legs (often smaller) that act as feelers for their surroundings and locating prey.

A group of arachnids you may be most familiar with are spiders. The local Darug people of the Sydney basin refer to spiders as marigung, marrayagong or danganuwa. 

All spiders belong to a larger groups of animals called arthropods. This means they have a segmented body covered in an exoskeleton and pairs of jointed limbs. 

Case study – Huntsman spider


Huntsman spiders are large, hairy, flat-bodied spiders. Their legs fan out sideways enabling them to walk forwards and sideways. They are found in a variety of colours and patterns but are mostly brown, black or grey. Some species are very large reaching over 16 centimetres in leg span.


Huntsman spiders occur Australia-wide and are usually found on tree trunks, under bark, beneath stones and even on the walls of houses. Their flat body allows them to squeeze into tight places.


Huntsman spiders eat insects and other invertebrates as well as small lizards and frogs. They hunt their food instead of using a web. Their fangs are large and can be used to hold the prey until it is paralysed by their venom.

Role in the ecosystem

Huntsman spiders control invertebrate populations and pest species such as the household cockroach. They are also food for other animals such as birds, geckos and spider wasps.

Spider anatomy


The cephalothorax is the head and thorax fused together. 

Huntsmen have eight eyes to spot approaching prey and predators.

Located at the front of the spider are the mouth parts called chelicerae, this includes their fangs at the end which they use to inject venom into their prey.

Beside the chelicerae are the pedipalps which the huntsman uses to feel and touch things around them and also helping to catch and hold onto prey. Males of some species use their pedipalps when mating.

All the spiders' jointed legs are attached to the cephalothorax. The legs have sensitive hairs to pick up sounds, vibrations and air currents.


The abdomen has no appendages except for spinnerets at the back end which produce silk.

Huntsmen spiders build silk egg sacks the size of a 20 cent piece to protect their eggs. These can often be found under bark.

Find out more

The Invertebrate Explorer digital book explores the incredible world of Australian invertebrates.

Students can use the book to investigate classification, features, adaptations and habitats of a variety of Australian invertebrates through narrated videos, stunning images, interactive activities and detailed text.

This book was designed by teachers to support the NSW Science and Technology K-6 Syllabus and NSW English K-6 Syllabus.

Content supports living world, Australian animals and class studies on invertebrates.

Download free from Apple Books.

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