Leptogaster obscuripes

Distinguished from other Asilidae by its small size, extremely slender and elongated body form, and disproportionately long, thin legs. The dark tarsi are a key feature separating L. obscuripes from congeners with paler legs. Leptogaster species can be confused with small damselflies or empidid flies due to their delicate build, but possess the characteristic robber fly features: a concave facial profile (mystax), spiny legs for prey capture, and a predatory resting posture with head raised. Specific separation from other Leptogaster species requires examination of leg coloration and male genitalia.

A small, slender robber fly with an elongated, cylindrical body. The legs are notably long and thin relative to body size, with dark or blackish tarsi that give the species its name ('obscuripes' = dark feet). The abdomen is typically elongated and tapering. The head is small with large, widely separated eyes in females and contiguous eyes in males. Wings are clear or lightly tinted with reduced venation compared to larger asilids.

Grassy meadows, open fields, and edges of woodlands with low vegetation. Prefers areas with scattered shrubs or brush where it can perch on grass stems and low vegetation to hunt. Often found in moist or mesic environments rather than arid habitats.

Documented from North America, with records primarily from the eastern and central United States. The exact range is imperfectly known due to identification challenges and undercollection of small asilids.

Adults active during summer months, typically June through August in temperate regions. Peak activity coincides with warm, sunny weather when prey availability is highest.

Perches horizontally on grass stems and thin twigs, often with the abdomen raised slightly and the long legs extended. Hunts small, soft-bodied insects such as aphids, small flies, and leafhoppers. Approaches prey with slow, deliberate movements before making a short flight to capture. Unlike larger robber flies, does not return to a fixed perch but may continue moving through vegetation while foraging.

Predator of small insects in grassland and meadow ecosystems. May contribute to natural control of pest populations such as aphids and leafhoppers, though quantitative impact is unknown.

No direct economic or medical significance. Occasionally encountered by entomologists and naturalists in field surveys. Too small to deliver a noticeable bite to humans.

• Leptogaster guttiventrisSimilar slender build and habitat preference; distinguished by pale or yellowish legs and abdominal spotting pattern
• Leptogaster flavipesOverlaps in range; has distinctly yellow legs rather than dark tarsi
• Empididae (dance flies)Similar small size and elongated body; empidids lack the concave facial profile and predatory leg spines of Asilidae, and often have more complex wing venation
• Coenagrionidae (damselflies)Similar perching posture and slender build; damselflies hold wings together above body at rest, have very large eyes that nearly meet, and are not predatory flies

• robber fly
• asilidae
• predatory fly
• grassland insect
• small asilid

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• Catalogue of Life