Myzinum frontalis

Males and females appear so different that they may be mistaken for separate species or even genera. Males are recognized by their slender build, long straight antennae, and prominent curled pseudostinger. Females are recognized by their larger, robust body, stout digging legs, and short coiled antennae. Species-level identification within Myzinum is extremely difficult even for experts; M. frontalis requires examination by a specialist using detailed morphological keys.

Sexual dimorphism is extreme. Males are slender-bodied with long, straight antennae and possess a curled, spine-like pseudostinger at the abdominal tip (part of external genitalia). Females are substantially larger with robust abdomens, stouter legs adapted for digging, and short, coiled antennae. Both sexes have a generally wasp-like appearance typical of the family.

Found in fields, meadows, and prairie habitats where host scarab beetle grubs occur in soil. Adults frequent flowering vegetation in open, sunny areas.

Eastern North America, west to the Rocky Mountains, and in the Southwest. Specific range boundaries within this broad area are poorly documented due to taxonomic difficulties in the genus.

Adults active from late summer through autumn (August to October), with peak activity coinciding with bloom of goldenrod and thoroughwort.

• Phyllophaga - parasitoidScarab beetle grubs (white grubs); female wasps dig up grubs, sting them into brief paralysis, and lay single eggs on them

Female wasps locate scarab beetle grubs underground, dig them up, sting them into temporary paralysis, and deposit a single egg on each. The wasp larva hatches, bores into the grub, and feeds internally while the host continues to live and feed. Eventually the wasp larva kills the host, pupates, and emerges as an adult the following summer.

Males are more frequently observed than females because they spend more time on flowers and gather in groups to roost on vegetation in early evening ("slumber parties"). Females are less conspicuous, spending more time underground searching for hosts. Males likely patrol flowers seeking females for mating.

Biological control agent of scarab beetle populations, particularly May beetle and June beetle grubs that can damage plant roots. As a parasitoid, it helps regulate soil-dwelling scarab populations in grassland and forest ecosystems.

Potential benefit to agriculture and forestry through suppression of scarab beetle grub populations, though quantitative impact is unknown. No documented negative impacts to humans; males possess a pseudostinger but cannot actually sting.

• Other Myzinum speciesExtremely difficult to distinguish morphologically; ten species recognized north of Mexico, and expert identification using specialized keys is required. Males of different species are especially challenging to separate.
• Male vs. female MyzinumSexual dimorphism is so pronounced that males and females of the same species were historically confused as different taxa; males are slender with pseudostinger, females are robust with digging legs.

• parasitoid
• sexual dimorphism
• scarab beetle
• soil-dwelling
• flower visitor
• autumn active
• biological control
• North America
• thynnid wasp

• BugGuide
• GBIF taxonomy match
• Bug Eric: Wasp Wednesday: Myzinum
• Southern Pine Beetle: How a Fellow Species May Help in Host Location
• Managing Southern Pine Beetle Infestations in a Changing Forest Environment
• Bug Eric: White Prairie Clover: An Awesome Blossom