Spider, line drawing.
- Andrew Howells
- © Australian Museum
Spiders belong to the Order Araneae.
What do spiders look like?
- Less than 1 mm - 180 mm in length.
- Constriction between cephalothorax (front portion containing head) and the abdomen.
- Abdomen without segments and is circular to cigar-shaped, some have spines and nodules.
- Most have eight simple eyes and size is variable. Two, four or six-eyed species exist, while some cave dwelling spiders have no eyes at all.
- For paralysing prey (i.e. fangs), for mashing and chopping up prey and for slurping liquids
- Mouthparts held in front or downwards at rest.
- Eight legs.
- Pedipalps (appendages between first legs and mouthparts) are leg-like, often with swollen tips in males.
- Cerci (tails) absent.
- Spinnerets (silk distributing organs) originate under the abdomen and sometimes extend well past the tip.
Where are spiders found?
- On land in all habitats.
- In leaf litter and under rocks, logs and bark.
- Below soil level in burrows.
- On plants on any surface.
- Suspended in webs and retreats.
- Some are found on or below the surface of fresh water.
- Domestic areas such as corners of the house.
What do spiders do?
- They are usually solitary, but a few live together.
- When disturbed they run under cover or move out of line of sight, run to constructed retreats or burrows, jump, drop to ground on draglines, remain still faking death, rear up exposing fangs, or bite.
- Almost all are venomous. The venom is delivered via fangs (mouthparts with poison glands) and is used to paralyse or kill prey, but may be used defensively if threatened. Few are harmful to humans.
- They are all predators, feeding mostly on other invertebrates but have been known to snare small vertebrates such as birds. After injecting their venom, spiders liquefy a victim's tissues with digestive juices.
- They have many types of hunting strategies. For example, passive hunters capture prey in webs, active hunters hunt particular prey using specialised techniques.
- They produce silk. The silk is used for a variety of purposes such as web-building, packaging prey and eggs, making draglines, and triplines, and casting nets.
- Many spiders are experts at camouflage, which they use to capture prey or to hide from predators. These spiders may behave in a particular way or use colouration, patterning, or structural features to help them blend in with their surroundings. In special circumstances they may also look or act like other invertebrates including ants, termites, wasps and even other spiders.
- Some have bright conspicuous colours to warn potential predators that they taste bad or can bite.
- They are active during the day or night.
What looks similar?
- Harvestmen (class Arachnida, Order Opilionida) are sometimes mistaken for spiders. However, they do not have a narrow waist, they are generally smaller (body length less than 10 mm), their pedipalps are long and antennae-like, and their body has segments.
- Some of the spiders that mimic insects such as ants and wasps can be difficult to identify. On closer examination they can be distinguished from ants and wasps by having only two major body regions, and eight legs.
- Some tiny spiders look like mites, but can be distinguished from mites by their narrow waist.