Microstylum

Microstylum can be distinguished from other Asilidae genera by the mystax being restricted to the oral margin and composed chiefly of stout bristles, rather than extending more broadly across the face. The genus includes some of the largest-bodied robber flies in their respective regions. In North America, Microstylum morosum and M. galactodes are separable by wing coloration: M. morosum has dark wings and body with thoracic pruinescence restricted to lateral margins, while M. galactodes has milky white wing membranes, reddish-brown body, and even whitish pruinescence covering the head and thoracic dorsum. M. galactodes is also generally smaller than M. morosum.

In North America, Microstylum galactodes occurs most frequently in short grass prairies and scrub lands. Microstylum morosum has been documented in mixed-grass prairie habitats, limestone glades, and atop mesas with scattered eastern redcedar (Juniperus virginiana). The species shows affinity for elevated terrain, with individuals observed hilltopping on the highest points of mesas and perching in scattered trees.

The genus Microstylum has a broad geographic range spanning North America, the Neotropics, and Madagascar. In North America, Microstylum morosum occurs in the southern Great Plains from Texas northward through Oklahoma and Kansas, westward to New Mexico, Arizona, and Colorado, with eastern extensions into Arkansas and Missouri. Microstylum galactodes has a slightly more western distribution, extending north only into western Oklahoma and western Kansas.

Microstylum morosum exhibits hilltopping behavior, with males flying to the highest points in the landscape to defend perches that provide vantage points for spotting females and competing males. Males and mating pairs have been observed perching and flying among scattered trees on elevated terrain. Individuals are generally wary and difficult to approach closely, though they may remain stationary when wind conditions reduce flight capability. Females have been observed with abdomen inserted into loose sand, presumably during oviposition, followed by rapid sweeping movements of the abdomen tip to cover the hole.

• Efferia group (including Triorla, Nerax)Similar large size and general body plan; distinguished by facial bristle arrangement and other structural characters
• PromachusOther giant robber flies in North America; Promachus species have different mystax structure and abdominal coloration patterns

• Asilidae
• Diptera
• robber flies
• giant robber flies
• Microstylum morosum
• Microstylum galactodes
• hilltopping
• prairie insects
• Great Plains fauna

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• The marvelously monstrous Microstylum morosum | Beetles In The Bush
• Asilidae | Beetles In The Bush | Page 2
• North America’s largest robber fly | Beetles In The Bush
• Observations of the Behavior of the Giant Prairie Robberfly, Microstylum morosum Loew (Diptera: Asilidae) at Terre Noire Natural Area, Clark County, Arkansas