Myzinum maculatum

Distinguished from other Myzinum species by subtle morphological characters requiring expert examination (species separation is notoriously difficult even for specialists). Males recognized by slender build, long straight antennae, and curled abdominal pseudostinger. Females recognized by robust abdomen, short coiled antennae, and stout fossorial legs. From other thynnid genera: Myzinum males uniquely combine pseudostinger with long straight antennae; females uniquely combine robust build with coiled antennae. Phenology helps: active late summer through autumn, associated with goldenrod and thoroughwort blooms.

Medium-sized wasp with striking sexual dimorphism. Males: slender, missile-shaped body; long, straight antennae; prominent curled spine (pseudostinger) at abdominal tip formed by external genitalia. Females: larger, robust abdomen; short, coiled antennae; stouter legs for excavation. Both sexes visit flowers, with males more frequently observed due to extended flower-visiting behavior.

Open habitats including prairies, meadows, and fields. Associated with turf grass environments where host scarab larvae occur. Adults frequent flowering vegetation, particularly autumn-blooming composites.

North America east of the Rocky Mountains and in the Southwest. Precise range boundaries undocumented; genus occurs across most of North America north of Mexico.

Adults active late summer through autumn (August–October), coinciding with bloom of goldenrod (Solidago) and thoroughwort (Eupatorium). Males observed in evening aggregations on vegetation.

• Phyllophaga - parasitoidScarab beetle grubs ('white grubs'), particularly May beetle larvae. Female wasps locate grubs underground, excavate them, sting to paralyze briefly, and oviposit. Larval wasp consumes host internally, eventually killing it.

Parasitoid development: female locates scarab grub below ground, digs to expose it, stings into brief paralysis, and lays single egg on host. Host recovers and reburies, but wasp larva hatches and bores into grub, feeding internally while host continues to feed and grow. Eventually larval wasp kills host, pupates, and emerges as adult the following summer. Uniparental or biparental emergence pattern not specified.

Males gather in evening aggregations ('slumber parties') on vegetation, bedding down in groups. Both sexes visit flowers for nectar; males more conspicuous due to extended flower-visiting. Females exhibit fossorial behavior, digging in soil to locate hosts. Males possess pseudostinger (non-functional in defense, part of genitalia) that appears intimidating but is harmless.

Biological control agent of scarab beetle populations, particularly in turf grass ecosystems. Acts as parasitoid, regulating grub densities. Adults contribute to pollination as flower visitors. Serves as food source for potential predators and parasites (thick-headed flies observed attacking related wasps).

Explicitly used as biological control agent for turf grass pests. Valued in integrated pest management for scarab grub suppression in lawns and golf courses. Non-aggressive; pseudostinger of males appears threatening but is harmless. No documented medical or economic negative impacts.

• Other Myzinum speciesTen species recognized north of Mexico, extremely difficult to distinguish morphologically even for experts. M. maculatum separation requires specialist examination using revised keys (Kimsey 2009).
• Male vs. female Myzinum (within species)Sexual dimorphism so extreme that genders were historically mistaken for different species, genera, or families. Recognition as conspecific requires knowledge of genus-specific dimorphism pattern.
• Other ThynnidaeMyzinum males distinguished by combination of pseudostinger and long straight antennae; females by robust build with coiled antennae and fossorial legs. Other thynnids lack this specific character combination.

The male pseudostinger is frequently mistaken for a functional stinger, causing unnecessary alarm. It is actually part of the external genitalia and harmless. The extreme sexual dimorphism has led to males and females being misidentified as different species or even higher taxa.

• parasitoid
• biological control
• sexual dimorphism
• turf pest management
• scarab parasite
• autumn active
• flower visitor

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• Bug Eric: Wasp Wednesday: Myzinum
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