Story: Spiders and other arachnids

Page 1. What is a spider?

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Insect or spider?

Although insects and spiders are often grouped together, they belong to different animal groups. Spiders are arachnids – technically Class Arachnida, which includes ticks, mites, scorpions and harvestmen (daddy-long-legs).

The most obvious way to distinguish insects from spiders is to count their legs. Insects have six legs, while arachnids have eight.

The Māori term for spiders is pūngāwerewere. Both insects and spiders are included in the term pēpeke, covering creatures with four or more legs that appear to be in a crouching position.

Spiders in New Zealand

Worldwide about 40,000 species of spider have been named, and many more remain undescribed. New Zealand has about 1,100 named species, most of which are endemic (unique to New Zealand). There are probably two or three times this number still to be described and named. A small but increasing number of spiders have been accidentally introduced from Australia and other countries.

All spiders in New Zealand belong to two groups: mygalomorphs and araneomorphs. About 90% of the spiders are araneomorphs.

Distribution

Spiders live in almost all parts of the country, from up to 3,500 metres high in the Southern Alps to below sea level along the coastline. In fact, for most of us, for most of our lives, we are probably never more than a metre away from a spider.

For humans, the garden is a safe place where we sniff flowers, pull weeds and rake leaves. But for spiders it’s a jungle out there – they catch, dismember and devour insects, delude and deceive each other, and are pulled apart by bigger predators.

Spider bodies

Spiders have a hard outer body called an exoskeleton. They have two main body parts, the cephalothorax and the abdomen, plus eight jointed legs. Most spiders have eight eyes.

Spiders have jaws (chelicerae) with fangs. Near their mouth, they have a set of leg-like appendages called pedipalps, which are used for handling prey.

Food

All spiders are carnivorous and their most common prey are insects. Many spiders are cannibalistic and also eat spider eggs. Almost all spiders use venom (injected through the fangs) to paralyse their prey before they start feeding. Glands inside the spider’s head are squeezed by muscles that force the venom out through the fang tips, just as a plunger pushes liquid out of a syringe.

Spiders feed on liquids and cannot take in solid food. They mix digestive fluid with the prey’s tissue and suck up the partially digested nutrients. While some spiders tear apart their prey, others leave the corpse almost intact, appearing to feed more like a suave vampire than a dismembering werewolf.

Weight watching

The total weight of all the insects eaten by spiders each year in New Zealand is many times greater than the total weight of the four million people that live here. That’s a lot of spiders eating a lot of insects.

Spider reproduction

A male spider produces sperm within its abdomen. It then builds a small silken web called a sperm web, on which it deposits a drop of sperm before sucking it up inside appendages called palps or pedipalps.

The male then inserts the palps inside an opening under the female’s abdomen and releases the sperm.

The female can store the sperm for long periods before using it to fertilise her eggs. She can control when the eggs are laid, so they hatch when it is warmer. The amount of maternal care varies greatly between species. Some stay with the eggs and babies until they leave the nest, while others initially protect their eggs with a tough silk covering, and then abandon them.

How to cite this page:

Simon Pollard, 'Spiders and other arachnids - What is a spider?', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/spiders-and-other-arachnids/page-1 (accessed 23 November 2017)

Story by Simon Pollard, published 24 Sep 2007