Attract Beneficial Thynnid Wasps with Summer-Blooming Native Plants

Thynnid wasps may look formidable with their large size and the male's curved pseudo-stinger, but these solitary wasps are gentle garden allies. Unlike social wasps that defend nests aggressively, thynnids have no colony to protect, making them perfectly safe to observe up close. Their presence offers a double benefit: adults act as pollinators while visiting flowers for nectar, and females hunt destructive scarab beetle larvae—including May beetle grubs—underground.

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Why Thynnid Wasps Are Valuable Garden Inhabitants

These parasitic wasps (family Thynnidae, genus Myzinum) don't build nests or stockpile prey. Instead, females locate beetle grubs in the soil—often by scent—and lay eggs directly on them. The hatching larvae consume the host from within, naturally suppressing root-feeding white grub populations that damage lawns and garden plants. Meanwhile, both sexes frequent summer blossoms, transferring pollen as they feed.

Range: Central, southwestern, and northeastern North America, including southern Canada and Central America
Habitat: Gardens, meadows, prairies, old fields, and farms
Active period: Mid-July through early September in northern regions (earlier farther south)

Identifying Thynnid Wasps

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Males have slender abdomens ending in a curved pseudo-stinger (not a true stinger), long antennae, and slender legs. Females are bulkier with broad, hairy legs adapted for digging. Both display black bodies with white, cream, or yellow markings. Larvae develop hidden underground on their hosts.

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How to Attract Them to Your Garden

Provide Prey Habitat

Avoid broad-spectrum pesticides that kill scarab beetle larvae—the wasps' essential hosts. A healthy grub population ensures female thynnids have reason to stay and reproduce.

Plant Their Favorite Nectar Sources

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Since they don't provision nests, thynnids only need floral resources. Plant these summer-to-fall bloomers:

• Mid-summer: Boneset (Eupatorium perfoliatum), Virginia mountain mint (Pycnanthemum virginianum), rattlesnake master (Eryngium yuccifolium), spotted beebalm (Monarda punctata), swamp milkweed (Asclepias incarnata), white prairie clover (Dalea candida)
• Late summer to fall: Goldenrod (Solidago spp.)

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Life Cycle Overview

After mating on flowers, females tunnel into soil to lay eggs on scarab or tiger beetle larvae. The wasp larva consumes its host, pupates underground, and overwinters. Adults emerge the following summer, completing a one-year cycle. Population numbers fluctuate with prey availability.

Shown: Mating pair on boneset (Eupatorium perfoliatum)