Spiders aren’t made as such, they have evolved as other insects have. They are essential as part of the ecosystem – they eat flies (for examples) and are then themselves eaten by birds and so on.
As Blanka said, they haven’t been ‘made’ – they’ve evolved. They are around because there is a space in the ecosystem that allows them to feed and reproduce. If there was no food for them or if they were easily eaten by predators before they had chance to reproduce then they wouldn’t survive and so there wouldn’t be any spiders
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