Proctacanthus milbertii

Large robber fly with a prominent beard. Distinguished from similar Promachus species by lacking the yellow and black tiger striping on the abdomen seen in P. hinei, P. rufipes, and P. vertebratus. Specific diagnostic features for separating P. milbertii from other Proctacanthus species are not documented in the available sources.

Open habitats with sandy or loose soil suitable for oviposition. Occurs in grassland and prairie environments where grasshopper prey is abundant.

Occurs across much of the United States. Documented from western Nebraska and ranges widely throughout the country.

Late season species, active in late summer and early fall.

Adults are aerial predators. A study in western Nebraska found grasshoppers (Orthoptera) made up 94% of prey captured. Nearly all remaining prey captures were other P. milbertii individuals. Prey species selection was determined by availability rather than size, with even the largest grasshopper species captured as readily as smaller ones.

Females lay eggs in crevices in soil. Larvae feed on soil insects, roots, and decaying plant matter. Development occurs within the soil.

Perches in open areas to ambush flying prey. Exhibits ferocious predatory behavior, capable of capturing large grasshoppers and even other individuals of its own species. Mating postures can resemble prey handling positions.

Significant predator of grasshoppers in prairie ecosystems, potentially contributing to grasshopper population regulation. Larval stage contributes to soil food web as a predator and detritivore.

• Promachus hineiSimilar large size and predatory habit, but distinguished by yellow and black tiger striping on abdomen and reddish femora
• Promachus rufipesSimilar large size and predatory habit, but distinguished by yellow and black tiger striping, black femora with orangish tibiae, and southeastern U.S. distribution
• Promachus vertebratusSimilar large size and predatory habit, but distinguished by more muted abdominal striping, two-toned legs with smaller dark areas dorsally on abdominal segments, and northern distribution

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• Catalogue of Life
• Magnificently Monstrous Muscomorphs | Beetles In The Bush
• Magnificently Monstrous Muscomorphs | Beetles In The Bush
• One-Shot Wednesday—Proctacanthus fulviventris ovipositing | Beetles In The Bush