All spiders are predators. They attack only live Insecta, other Araneae, and other invertebrates. A few very large spider species attack small vertebrates like Squamata, Pimephales notatus, or Anura, but this is rare. Spiders are famous for trapping their prey in webs of sticky silk, but many of them are wandering predators who don't use silk to catch prey.
"One particular hydraulic device is worth a little more attention here, partly because its existence comes as yet another surprise and partly because it achieves antagonism for contractile muscle in an unusual way. The eight legs of a spider differ little from the six of an insect, but a curious special feature of spider legs has been known for almost a century. While properly equipped with flexor muscles (ones that decrease the angle between one segment and another), they lack the antagonistic extensor muscles (ones that increase that angle toward 180 degrees). Biologists casually assumed that elasticity of the interarticular membranes provided the antagonistic force, not on the face of it an unreasonable idea. But Ellis (1944) remembered that spiders die with legs severely flexed. If elasticity did the extension, they would more likely die with legs extended or at least not so flexed--as do insects. He found that cutting off the tip of a leg prevented re-extenson until the tip was resealed; and he found that mild exsanguination reduced a spider's ability to extend any of its legs. He suggested that extension in spider legs was hydraulic, not muscular or elastic. The idea was confirmed by Parry and Brown (1959), who measured resting pressures of 6.6 kilopascals and transient pressures of up to 60 kilopascals (over half an atmosphere) in spider legs. An isolated leg could lift more weight as the pressure inside it was increased, and the spiders turned out to have a special mechanism to seal off a joint that prevented fatal depressurization when a leg was lost." (Vogel 2003:421) Learn more about this functional adaptation.
Barcode of Life Data Systems (BOLD) Stats Specimen Records:93416 Specimens with Sequences:70176 Specimens with Barcodes:67332 Species:5866 Species With Barcodes:5147 Public Records:65137 Public Species:2922 Public BINs:7360
Spiders often have good camouflage, and many of the wandering hunter species hunt at night when big predators can't see them. Many spiders build a retreat of silk to hide in too. Some are quick runners, and will just run away if they can. These may use their silk as a safety line, jumping off into the air with a silk thread attached so they don't fall.
Spiders scare a lot of people (usually this is unnecessary). A few spider species have venom that is dangerous to people, but spider bites are actually pretty rare. They get blamed for a lot of skin injuries that are not actually spider bites. Most spiders have such small weak fangs that they couldn't break a person's skin, even if they wanted to.
Negative Impacts: injures humans (bites or stings)
Based on studies in: Norway: Spitsbergen (Coastal) Canada: Manitoba (Grassland) Russia (Agricultural) Malaysia (Swamp) England: Oxfordshire, Wytham Wood (Forest) Namibia, Namib Desert (Desert or dune) USA: Alaska (Tundra) USA: Arizona, Sonora Desert (Desert or dune) India, Rajasthan Desert (Desert or dune) USA: Massachusetts, Cape Ann (Marine) USA: California, Cabrillo Point (Grassland) Puerto Rico, El Verde (Rainforest)
This list may not be complete but is based on published studies.