Usually spiders prey on insects and other spiders. Of course it varies, from different species. For example, the Goliath spider eats: frogs, small snakes, beetles, insects, lizards, bats and young rats. Then you have the tarantula spider, which eat: crickets, cicadas, grasshoppers, sow bugs, caterpillars, and beetles. They also don't mind eating rodents, but they aren't preferred , due to the size of the tarantula. There are so many different species of spiders, that eat a variety of things; dead or alive.