Asilus used to be a catch-all for many different groups of robber flies, but it now is represented by only a single species in North America.
Asilus sericeus
Large with a dark stripe down the middle of the scutum (thorax), so it could be confused with Triola interrupta. However, note the dark wing with pale wing veins and reddish-brown color overall. Legs pale brown.
Size: 20-28 mm
Range: Northeastern U.S. and Canada
FL Range: Unknown. I can’t find any records, but it is included in Fisher & Wilcox’s catalogue for Florida.
Season: May-August throughout range



References
Fisher, E. M., & Wilcox, J. A. (1997). Catalog of the robber flies (Diptera: Asilidae) of the Nearctic Region. EM Fisher.
Hine, J. S. (1909). Robberflies of the genus Asilus. Annals of the Entomological Society of America, 2(2), 136-170.