Why do spiders exist

The world' s continents, with the plants and animals on them, have drifted together and broken apart over many millions of years. Some million years ago, Australia was part of the southern supercontinent of Gondwana. When Gondwana broke up, spiders were isolated on separate continents, where they evolved independently into new but related spider groups.

The recognition of related plant and animal taxa on widely separated continents like Australia. Spider species that are found in many places are often good travellers. Many of these spiders get around by behaviour called ballooning. Young spiders, and even small adults of some species, put out silk threads which are caught by the wind, carrying them up and away.

Many land close by, sometimes swathing the landscape in gossamer silk; but others may travel long distances across land or sea. Ballooning helps maintain and extend the distributions of these spiders.

Spiders as different as orb weavers and wolf spiders disperse by ballooning. Many events, like climate change or rising sea levels, can result in animals like spiders becoming isolated in 'refuge' habitats, like caves, mountain tops and islands, where they are unable to survive in the 'hostile' areas surrounding their refuge.

These isolated populations are often small and can be subject to considerable random genetic variation - a 'bottleneck' effect. Such spiders may not only evolve into new species but may also become specifically adapted to living in specialised habitats like caves.

These highly adapted species cannot survive outside the cave refuge even after surface climatic conditions have improved. It is logical that such species are poor dispersers that need to spread only over relatively short distances by walking. Refuge habitats are important for conservation because many of the animals and plants that live in them are not found anywhere else. Their presence gives us valuable information about evolutionary processes and environmental history. Wind and rain damage their structure, while the gluey coating on the spiral thread that ensnares flying insects is rendered ineffective by pollen and dust.

As a result the webs are often rebuilt every night — an operation requiring the manufacture of some 20 metres of silk. Abandoning one web and building a new one every night would be pretty wasteful. Instead, some orb-web-spinners recycle the amino acids that make up the silk proteins by ingesting the silk as they systematically dismantle their damaged webs. Other species simply discard the old silk but one American species uses it to wrap its egg sac. Silk is used to build webs and egg sacs, wrap up prey, help dispersal of young and as safety lines when escaping predators.

Water spiders also use silk to hold an underwater air supply. Spiderlings disperse using silk. They travel to a high point, raise their abdomens and let out one or more strands.

On warm days with rising air currents, the spiderlings are lifted into the air and carried away. Spiders eat large numbers of insects. Exceptionally, one spider may take hundreds of very small flies in one day. Edible prey is wrapped up in silk. The remains can often be seen attached to the web for those spider species that build them. Crab spiders are sit-and-wait predators.

They are often seen perched on garden flowers with their long front legs held out, crablike, to seize insects visiting the plant. Wolf spiders are brown and furry, and on sunny days large numbers can be seen running through vegetation on the edge of a pond, for instance hunting prey. On sunny walls, black-and-white striped jumping spiders can be seen stalking and pouncing on prey. The very distinctive nocturnal woodlouse spider Dysdera crocota , which has a reddish-brown body and legs, a pale abdomen and powerful fangs, hunts woodlice under stones and flowerpots.

Spider venom has the potential to act as a safer painkiller and may be able to treat strokes, muscular dystrophy, and of course, is used for antivenom in cases of harmful spider bites. These pests play an important role in our ecosystem as predators to other insects. Determining the importance of spiders depends on who you ask. A gardener or farmer is likely to recognize how helpful they are at preventing pests from destroying crops. A doctor, scientist, or engineer may appreciate the innovative possibilities related to the study of spiders.

Being scared of them is a normal response, and there are a few types of dangerous spiders , including the black widows and brown recluses. However, most species generally prefer to avoid contact with people. Even in instances of spider bites , healthy adults can usually survive without serious consequences. Keeping spiders outside where they belong is the best way to keep everyone safe, happy, and healthy. Keep your home pest free with simple, effective solutions.

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