These tiny hunters are closely related to Stichopogon, and both have widely separated eyes. These are our smallest robber flies and are only 3 to 5 mm. They still have the same behavior as other robber flies — especially when they fly out from a perch and return to the same perch — so if you’re tuned in to robber fly behavior, you may have a chance at finding these. Otherwise, you may need to already be on your hands and knees to notice them. They are that tiny!
Below are a few photos I’ve taken to try to illustrate how small they are.
There are two species in Florida with very different habitats. T. nigra occurs throughout the southeast (north to NJ) along river floodplains, and T. arenicola is found in scrub on sand ridges in central Florida.
Townsendia arenicola
Scarbrough notes T. arenicola has a paler abdomen than T. nigra, but the abdomen of T. arenicola is downright reddish in life. Dense gray and brown tomentose pattern on scutum (microscopic hairs cause the top of the thorax to have gray and dark brown color). Sparse and short hairs on the head and scutum (if you can see them). Two tergosternal bristles. Scarbrough notes wide gray tomentose bands on apical margins of abdominal segments 2-6, but this may be difficult to see. Occurs in scrub on sand ridges in central Florida. May et al. (2012) refers to this as the Pygmy Scrub Robber Fly.
Size: 2.7-3.4 mm
FL Season: June – August
FL Range: Thought to be a Lake Wales Ridge endemic, but recently found on other scrub ridges in central Florida by Brandon Woo. Currently known from Highlands, Indian River, Osceola, Manatee, Martin, and Polk Counties. There is a Townsendia specimen at UCFC from Orange County sand-pine oak scrub that is likely T. arenicola if the genus ID is correct.
Townsendia nigra
Black abdomen, slightly whitish pruinose on sides and at base. Longer hairs on head and scutum. Three to five tergosternal bristles. Legs dark yellowish red. Occurs near rivers.
Size: 4-5 mm
FL Season: May – June
FL Range: Known from north Florida (Alachua & Columbia Counties) and the panhandle (Okaloosa County).
Range: Occurs throughout southeast (north to NJ).
References:
Back, E. A. (1909). The robber-flies of America, north of Mexico, belonging to the subfamilies Leptogastrinae and Dasypogoninae. Transactions of the American Entomological Society (1890-), 35(2/3), 137-400.
Martin, C. H. (1966). The genus Townsendia Williston in Mexico (Diptera: Asilidae). Journal of the Kansas Entomological Society, 542-551.
May, A., Otte, H., Dunlap, J., Dearborn, K., & Interns, S. 2012. Final Report on Project T-15-D: Lake Wales Ridge Scrub Arthropods.
Scarbrough, A. G., Norden, B. B., & Krombein, K. V. (1995). A new species of Townsendia Williston (Diptera: Asilidae) from Florida with notes on its association with Perdita graenicheri Timberlake (Hymenoptera: Andrenidae). Entomological Society of Washington (USA).
Robber Flies of Florida 