Grass Skipper

With Apaustus gracilis you were really very close. Take a look at the colors of the antennae. Apaustus gracilis has complete black antennae tips and the markings/venetion seem in my eyes being stronger and slightly "thicker" compared to yours: http://butterfliesofamerica.com/apaustus_g_gracilis_live1.htm That's why I think it is Callimormus radiola. Please, looks at these pictures to compare the antennae with the whitish part at the end of the club and the markings: http://butterfliesofamerica.com/images/Hesperiidae/Hesperiinae/Callimormus_r_radiola/Callimormus_r._radiola_COSTA_RICA_Moravia_Route_10_November_2010_CATCHICK_1.JPG http://butterfliesofamerica.com/images/Hesperiidae/Hesperiinae/Callimormus_r_radiola/Callimormus_r._radiola_MEXICO_CHIAPAS_07-VIII-2008_BERTHET..JPG Here is again an Apaustus gracilis to compare: http://butterfliesofamerica.com/images/Hesperiidae/Hesperiinae/Apaustus_g_gracilis/Apaustus_g_gracilis_La_Selva_CR_22-I-08_KG_3.jpg