Many factors affect the distribution and evolutionary history of spiders. These involve geological, environmental, genetic, ecological and behavioural processes.
You can see spiders by day and night in almost every habitat on earth. The only places where there are no spiders are the polar regions, the highest mountains and the oceans. A few spider species have invaded the ocean's edge, living in the rock and coral crevices of the intertidal zone.
How do spider relocate?
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.
Conserving spiders and their habitat - why should we?
Spiders are an important and fascinating part of our natural environment. Their webs are wonders of natural architecture. They have major ecological and agricultural roles as killers of insects. Both their venom and silk are being used in medical research (stroke treatment) , pest control (insect specific pesticides) and fibre technology (transgenic biosilk production).
In many parts of Australia spider populations are threatened because their habitats are being destroyed by the clearing and degrading of bushland. Conserving spider habitat not only saves the spiders but also the whole ecosystem of which they are a part. Habitat conservation is an essential element of maintaining sustainable ecosystems.
Bushland remnants are important habitats for spiders in rural areas. Grazing sheep and cattle damage vegetation, trample the ground and compact the soil. This can decimate local populations of ground dwelling spiders. Not only does trampling directly destroy their habitats, it can also make the soil so hard that burrowing spiders cannot recolonise the area.
Many different spiders live alongside humans exploiting the nooks and crannies of houses, sheds and gardens. They are good to have around because they eat lots of insect pests. Very few are harmful.