This one is interesting: the genus Argyrodes is known for being kleptoparasites. They can spin their own webs, but prefer to reside in the webs of other, usually larger, spiders. Some species may wait until the host is vulnerable (such as after a molt) then attack and consume it, but most will simply feed off small captured prey the host can't be bothered with.

Appropriately, the Japanese name for the genus means "freeloader spider", with this species being the "silver freeloader spider".