The Florida species of Andrenosoma were formerly classified as Dasyllis. They are in the Andrenosomini tribe, which contains 117 species worldwide, all of which live on fallen, dead trees (Fisher, 1986). They are fuzzy and look similar to Laphria.
Thorax has alternating silver gray and black coloration on mesonotum (top of thorax). The last 3 to 4 abdominal segments are reddish-brown.
Habitat: Found in dry, sandy locations with fallen trees. It perches on logs, trucks, and stumps in sunlight. Eric Fisher noted these were attracted to forest fires in California, and that females would oviposit in still-smoldering trees! (Fisher, 1986)
Size: 15-20 mm
Range: Throughout the U.S. and southern Canada
FL Range: Recorded in central Florida — likely throughout.
Season: March – May (through August outside of Florida)
Andrenosoma cruentum is similar to several neotropical species which have not been recorded in Florida. It can be distinguished from A. fulvicaudum by the abdomen and thorax. Abdominal segments 6 and 7 and genitalia are reddish-brown, whereas the last three and sometimes 4 segments are reddish-brown in A. fulvicaudum. The mesonotum (top) of the thorax is entirely dark gray or brown in A. cruentum, lacking silver-gray.
Habitat: Found among mangroves — both red mangrove (Rhizophora mangle) and black mangrove (Avicennia nitida), usually on dead branches and stems (Richard Westcott, per. comm, in Fisher, 1986).
Size: 17-25 mm
Range: Southern Florida and Cuba
FL Range: Miami-Dade and Monroe Counties. Deering Estate, Virginia Key, and Key Biscayne in Miami-Dade and Florida Keys. June 2022 edit: Population found at Ding Darling NWR in Lee County!
FL Season: May – September
Fisher, E. M. (1986). A Reclassification of the Robber Fly Tribe Andrenosomini: With a Revision of the Genus Dasyllis Loew (Diptera: Asilidae) (Doctoral dissertation, University of California, Riverside).