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Spiders and other arachnids

by  Simon Pollard

New Zealand’s spiders are mostly harmless to humans, busily trapping or hunting a vast number of insects. They are spinning their webs everywhere, from the mountains to the coast, and thousands of species have yet to be named.


What is a spider?

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.


Webs

Why do spiders produce webs?

We usually see spiderwebs more often than we see spiders. About half of all spiders build webs to catch prey, while the others use stealth, speed and ambush, and are commonly called hunting spiders.

Spiderwebs effectively increase the size of the spider and provide it with information that would normally be outside the range of its senses. A spider’s web extends the range over which the vibrations of a moving insect can be felt.

Web spiders use their feet to ‘listen’ for the vibrations that signal that their prey has touched the silken lines of the web. They then run across to the prey and immobilise it with venom. They add glue droplets to silk or entangling threads, so that prey stick to the web.

Producing silk

At the end of their abdomen, spiders have tiny tubes called spinnerets, used for producing silk. In the abdomen are silk-making glands, inside which the silk is a liquid protein. The spider squeezes silk from these glands and into the spinnerets. It uses hairs on its fourth pair of legs to pull the liquid silk through the spinnerets. The tension of this movement makes the protein molecules line up, and the silk solidifies into a thread.

Spiders use silk in different ways throughout their lives – to trap and wrap up prey, as a safety line if they fall, to build nests, and to protect their eggs.

Spider silk is the strongest natural fibre known. One strand is about five times stronger than a strand of steel of the same width. Silk is also very elastic and can be stretched to 130% of its original length.

Why don’t spiders get caught in a web?

Many spiders have a coating of oil on their feet, which stops them from getting glued down. Most also tread carefully, to ensure that they don’t get tangled. But sometimes an unfortunate spider can get caught in a web.


Mygalomorphs – tarantula relatives

Only about 10% of New Zealand spiders are mygalomorphs, but this group includes some of the more spectacular species.

Most New Zealand mygalomorphs are large and stocky, with a body length up to 3 centimetres, and are related to tarantulas. Mygalomorphs have to strike downwards at their prey, and their fangs move up and down.

Catch a beetle

If you rest your hand on the ground, then raise the two fingers next to your thumb like a spider’s fangs, you will see how you have to lift your hand slightly.Your finger fangs can stab at the beetle that just walked by. This is how mygalomorph spiders strike at their prey.

Tunnel-web spider

The tunnel-web spider Porrhothele antipodiana (Family Hexathelidae) is found throughout New Zealand. Living among logs and loose stones, it builds silken tunnels along which it can quickly reach prey or run away from predators.

Although closely related to the very venomous Australian funnel-web Atrax robusta, tunnel-webs are harmless. However, they have big fangs and have been known to bite.

Trapdoor spider

The common trapdoor spider (Misgolas species) lives in a silken tube with a hinged trapdoor at the top. It waits with its front legs poking out from beneath the lid, and detects the vibrations of insects walking near the trapdoor. When the insect is within striking distance, the trapdoor flies open, and the spider leaps from the burrow and pulls the prey down the tube. The remains of victims are left next to the trapdoor.

New Zealand cave spider

The unique New Zealand cave spider, Spelungula cavernicola, has some features that are intermediate between mygalomorphs and araneomorphs.

Discovered in the Ōpārara caves near Karamea in 1957, it has since been found in other caves. It lives in the twilight zone near the mouth of caves rather than in full darkness, and feeds mainly on cave wētā, supplemented by blowflies.

Some cave spiders hang from the roof of caves on draglines, and feed and moult in this position. There are records of a cave spider grabbing a wētā, then letting itself down on a dragline, wrapping the prey in silk and eating it.


Araneomorphs

Most New Zealand spiders are araneomorphs. Their fangs move sideways (imagine your thumb and forefinger coming together) rather than up and down like the mygalomorphs. With this type of fang, araneomorphs do not need to have their prey on a solid surface to strike, and can exploit a far wider range of habitats than the mygalomorphs.

Spiders do not fly, but a lot of their food comes from insects that can. Araneomorphs can directly catch flying insects, and also use webs as aerial filters.

Orb-web spider

The common orb-web spider Eriophora pustulosa is seen in gardens throughout New Zealand. Often its lines are weighed down with drops of morning dew, making the web look like a diamond necklace.

At night the spider either remakes or repairs the web, and then waits for insects to fly into it once again. The spiralling lines have tiny glue droplets which stick to an insect that touches the web. Once the prey has been caught, the spider wraps it in a shroud of silk so it cannot escape. The ‘spokes’ of the web do not have glue, and are used as attachment points for the spiralling threads.

Spinning a tale

In 1981 the novelist Patricia Grace published the children’s book Te kuia me te pungawerewere or The old woman and the spider. The spider is probably the common grey house spider, Badumna longinqua. The story tells of a spinning contest between the two.

Grey house spider

The grey house spider Badumna longinqua is probably the most common spider in New Zealand, and lives in most homes and gardens. It arrived from Australia in the 19th century.

Badumna has a comb of special hairs on its back legs, to comb out the threads from its spinnerets. It builds a cobweb with a narrow tube and traps prey with a fine ‘wool’ of threads between the structural threads. Tangled prey vibrate the lines, alerting the spider.

Huntsman as stuntman

The Avondale spider (Delena cancerides) is a huntsman spider from Australia, but in New Zealand it seems to occur only in the Auckland suburb of Avondale. This is one of New Zealand’s largest spiders, up to 20 centimetres across. It was used in the 1990 film Arachnophobia instead of a tarantula because it can run across walls, while tarantulas tend to fall off.

Hunting spiders

Hunting spiders rely on stealth rather than webs. Two common species are crab spiders and jumping spiders.

Crab spider

Crab spiders (Thomisidae family) are common on garden plants, but are well camouflaged. They wait with outstretched arms for insects to land on the plant, then grab them. Crab spiders usually inject venom into the head of their victim and suck out its insides. They leave the body intact.

Jumping spiders

Jumping spiders (Salticidae family) have eyesight to rival a primate, and a mammal-like cunning. They will stalk a fly on the edge of a table, then walk hidden towards it, checking its position before pouncing. If the spider has to approach directly, it will crouch down and move very slowly until close enough to pounce – like a cat stalking a bird. When you look at a jumping spider closely, it will often raise its head and look back.

Hey, good-looking

Many jumping spiders look like tiny primates. Some have moustache-like tufts, punk-style haircuts and jewel-coloured scales decorating their faces and bodies, to attract mates and scare off rivals. Males attract a mate by waving their legs and posturing.

Water spiders

The common water spider Dolomedes aquaticus has muted colouring that blends with river stones. It is not normally seen during the day, but sits and waits for prey after dark, and can survive under water for short periods.


Venomous spiders

New Zealand has no harmful animals like venomous snakes, scorpions or venomous insects, so its sole venomous native spider – the rare katipō – has almost mythical status. Since the late 19th century there have been accidental introductions of the venomous redback and white-tailed spiders from Australia.

Katipō

Māori knew of a venomous spider that lived on or near some of the warmer North Island beaches. They called it the katipō, which means ‘night-stinger’. The scientific name is Latrodectus katipo.

Only the adult female katipō bites. A fully-grown female is about the size of a garden pea. It is black, with a bright red stripe on its back.

Katipō are naturally shy, and would probably only bite if accidentally squashed. Few New Zealanders have ever seen one, let alone been bitten. Despite their reputation, there is no solid evidence that anyone has died from a katipō bite in the last 100 years.

Rarer than a kiwi

Katipō spiders are now classified as a threatened species. It is illegal to collect or deliberately kill them. The decline is probably because of changes in the beach habitat, especially the replacement of native pīngao with marram grass. Experts agree that there are now fewer katipō than another national icon, the kiwi.

Redback spider

In recent years small numbers of the Australian redback spider (Latrodectus hasselti) have been recorded in different parts of New Zealand. Because it prefers dry sheltered places, it is often found in outbuildings. There appear to be only small, localised populations, but there is some possibility of the spider spreading further through much of the North Island and northern parts of the South Island. While New Zealand’s damper climate does not favour the redback, their liking for modified urban environments could provide shelter from the weather.

White-tailed spider

Two species of the Australian white-tailed spider, Lampona cyclindrata and Lampona murina, have been recorded in New Zealand, and appear to have been present for at least 100 years. Both live in cracks and crevices, sometimes on the outside of houses.

The bite of the white-tailed spider is not poisonous to humans. There has been considerable publicity about serious skin infections, called necrotic lesions, that may develop near bites. In a recent Australian study of 130 confirmed white-tailed spider bites, 75% of people said the bite was less painful than a bee sting, and nobody developed lesions.


Other arachnids – spider relatives

Mites

Mites (Acari order) are found in most habitats where animals exist. They are so small that they are often overlooked. The most abundant mites live in the upper layers of the soil, playing an essential role in the breakdown of organic content.

Pseudoscorpions

Pseudoscorpions are small scorpion-like arachnids common throughout New Zealand. They are usually no more than 5 millimetres long, and are often mistaken for baby scorpions. They are predators, and use their pincer-like pedipalps to catch small insects. Unlike scorpions they do not have stinging tails.

Pseudoscorpions are shy and retiring. Sometimes they hide under stones or foliage, but the best way to find them is to sift leaf litter from the forest floor on to a dish, and then wait for them to move.

Harvestmen (daddy-long-legs)

Harvestmen (Opiliones order) seem the most bizarre of all the arachnids. In fact they are the most harmless creatures, being one of the few arachnid groups that do not use venom.

Although native harvestmen are numerous and widespread in New Zealand, the most common is the introduced European species Phalangium opilio (known as daddy-long-legs), found throughout the country. Because they were so common in English fields during the harvest, the group has become known as harvestmen.

New Zealand has a large number of unique species. They are divided into two groups: the suborder Laniatores (short-legged harvestmen) and the suborder Palpatores (long-legged harvestmen).

Short-legged harvestmen are known for their spiny, knobby bodies and stout, spiny pedipalps which are used for grabbing prey. The long-legged harvestmen have very thin legs, about 20 times the length of their body.

The males in the genus Megalopsalis have black bodies and enlarged, two-segmented chelicerae (mouth appendages) that tower above their body like a crane. The females look more colourful, with yellow, brown, green and red patterns on their bodies. For many years each sex was thought to be a separate species.


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How to cite this page: Simon Pollard, 'Spiders and other arachnids', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/spiders-and-other-arachnids/print (accessed 18 November 2017)

Story by Simon Pollard, published 24 Sep 2007