As predators, most spiders feed on other animal life. Given the great variety in spider sizes, anatomy and hunting practices across the order, prey species vary from small flies and insects -- in the case of smaller net-casting spiders -- to larger species of insects and even rodents and other small animals -- in the case of larger spiders and tarantulas. Many of the defining characteristics of the spider order Araneae, such as venomous fangs, are adapted to this predatory role in the food chain.
Perhaps the best-known spider hunting technique is the setting of insect-trapping webs. Many species of spiders use this method, spinning sticky webs of protein fibers that serve both as a shelter and a trap that entangles insects flying nearby, working much like an adhesive fly trap. Certain species of spiders have also been observed casting these sticky fibers in the direction of prey to snare unsuspecting insects, while larger spiders like tarantulas are usually ambush hunters, hiding in camouflaged shelters and surprising prey with a venomous bite.
Unlike most larger predators, spiders do not have teeth and a complex digestive system capable of processing animal protein. As a result, spiders can only ingest liquids and must break-down the tissues in their prey before consuming them. Spiders either pump digestive enzymes onto their prey and ingest the liquefied remains or combine that process with a grinding procedure using chelicarae, the antennae-like projections near the mouth of a spider. This external digestion process is also useful for feeding young.
While most spiders are predatory hunters, a few species exhibit other feeding behaviors. A few families of spiders have been known to feed on plant nectar or pollen trapped in their nets. The jumping spider, for example, feeds mostly on plant matter from acacia shrubs, although it complements its diet with small insect species. In other cases, spiders also act as scavengers, feeding on dead insects and even discarded human wastes such as egg yolks.