Lasiopogon chaetosus

Distinguished from other Lasiopogon species by its exceptionally dense and prominent bristling (chaetotaxy), particularly on the legs and abdominal tergites. The species name 'chaetosus' (meaning 'bristly' or 'hairy') directly references this diagnostic feature. Separation from congeners requires examination of male terminalia and female ovipositor structure, as well as detailed patterns of bristle arrangement on the legs and body. Distinguished from other robber fly genera by the combination of small size, ground-perching behavior, and the characteristic Lasiopogon facial profile with a slightly concave mystax.

Small to medium-sized robber fly with a notably bristly or setose body surface, as indicated by the specific epithet. Members of Lasiopogon typically have a slender build, a relatively short and stout proboscis adapted for piercing prey, and eyes that are widely separated in females and contiguous or nearly so in males. The body is usually covered with prominent bristles (macrotrichia) on the legs and abdomen. Wing venation follows the typical asilid pattern with a distinct anal cell. Coloration is generally dull, often grayish or brownish, providing camouflage against ground substrates.

Open, dry habitats with exposed mineral substrates including sandy areas, gravel bars, rocky outcrops, and sparsely vegetated ground. Often associated with riverbanks, lake shores, and other riparian zones where bare ground is available for perching and nesting. Vegetation cover is typically low, allowing unobstructed flight paths for aerial hunting.

Endemic to western North America. Documented from California, with records extending into adjacent regions of the Pacific coastal states and interior western United States. The precise range boundaries remain incompletely documented due to limited collecting effort and taxonomic revisions within the genus.

Adult activity period spans late spring through summer, with peak emergence typically occurring in May through July. Activity is strongly dependent on local temperature and moisture conditions; adults are most active during warm, sunny periods when prey availability is highest.

Perches on bare ground or low rocks, waiting in ambush for small flying insects. Upon detecting prey, makes short, rapid aerial pursuit and captures prey in flight using spiny raptorial legs. Returns to perch to consume prey, using the piercing proboscis to inject digestive enzymes and suck liquefied tissues. Males establish and defend perching territories suitable for prey capture. Mating occurs at or near perching sites.

Predator of small Diptera and other minute flying insects, contributing to regulation of prey populations in open, early-successional habitats. Serves as prey for larger predatory insects, spiders, and birds. Larval stages (unknown for this species) typically function as predators or scavengers in soil food webs.

No direct economic importance. Occasionally encountered by entomologists and naturalists in appropriate habitats. Like all robber flies, poses no threat to humans; does not bite unless handled, and venom is harmless to people.

• Lasiopogon cinctusOverlapping range and habitat preference; distinguished by less dense leg bristling and differences in male terminalia structure
• Lasiopogon aldrichiSimilar size and ground-perching behavior; separated by patterns of bristle density on the hind femora and abdominal coloration
• Stenopogon spp.Congeneric subfamily members with similar habits; distinguished by more elongated body form, longer antennae, and different wing venation patterns
• Proctacanthus spp.Larger robber flies sometimes found in similar open habitats; distinguished by greater size, more robust build, and different perching posture

• robber fly
• asilid
• predatory fly
• ground-perching
• western North America
• sand habitat
• bristly

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