Daggerwings are similar in wing shape to Swordtails and Swallowtails (Papilionidae), but Papilionidae have 6 legs whereas Marpesia and all other Nymphalidae genera have only 4 legs. 
Another feature to look for is the antennae.
In all Papilionidae species these are recurved at the tip, but in Marpesia they are straight.

Reserva Ecologica Taricaya, Puerto Maldonado, Peru, 15 & 16 June 2009