Kleptoparasitism describes the behaviour of a few different genera of spiders that steal the food from other spiders. The most obvious example one is likely to come across is the tiny Dew-Drop Spider (Argyrodes spp) feeding off the discarded prey remains of the massive Golden Orb Web Spider (Nephila spp). Some species will even feed on the web itself for added protein.
Dew Drop Spiders come in all sorts of funny shapes, with large bulbous abdomens, as shown here, or long protruding ones.
Above: Nephila fenestrata - BLACK LEGGED NEPHILA (Golden Orb Web Spider), whose massive web harboured at least 3 Kleptoparasitic Dew Drop Spiders.