I originally got the idea of getting guineas when I google-searched for an effective organic method of controlling the plague of grasshoppers that damaged my vegetable garden the first year I planted it. A couple of sites recommended guineas....Three years later here I am - proud tender of 14 guineas who have solved the grasshopper problem in less than 2 complete summers. And mine only free range about 2 times a week. (Because I'm hawk phobic after losing one bird the first fall I has them.)
They also love: Japanese beetles, crickets, cicadas, katydids, flies, little moths that fly out of the grass, and I'm supposing ticks although I cannot claim to have seen one catch and eat a tick!