Sphex pensylvanicus (Great Black Digger Wasp)

Species Overview

• Scientific name: Sphex pensylvanicus

• Common name: Great Black Wasp

• Family: Sphecidae (thread-waisted wasps)

• Native range: Widely distributed across North America, from southern Canada through most of the continental U.S., into northern Mexico. Common in the Midwest, including the Chicago region.

• Appearance: Large (up to 1.5 inches), completely black with iridescent blue highlights on wings and body; long, slender “thread-waist.”

Ecological Role

Predator of pest insects

• Adults hunt katydids, grasshoppers, and other Orthoptera — often species that can damage crops and garden plants.

• Paralyzes prey with a sting and brings it to an underground burrow as food for larvae.

• This makes them valuable natural biocontrol agents.

Pollinator

• Adults feed on nectar, making them important pollinators of many summer-blooming native wildflowers.

• While not specialized to one plant group, they are efficient cross-pollinators because of their large size and frequent foraging.

Ecosystem link

• Serves as prey for birds, spiders, and other predators, linking higher and lower trophic levels.

• By hunting herbivorous insects, they indirectly support plant health.

Lifecycle

1. Emergence:
   Adults typically emerge in mid-to-late summer (July–August in Chicago).
   Males emerge first, establish territories, and patrol for females.

2. Mating:
   Males guard sunny patches of vegetation and intercept females for mating.

3. Nesting:

   • Solitary (not colony-forming like yellowjackets).

   • Females dig burrows in sandy or loose soil, often in open, sunny spots.

   • Burrow may be up to 12 inches deep with several side chambers.

4. Hunting and provisioning:

   • Female hunts katydids/grasshoppers, stings to paralyze them, carries prey to burrow.

   • Places 1–3 prey items in each chamber with a single egg laid on the first prey.

5. Larval stage:

   • Egg hatches within ~3 days; larva feeds on the still-living prey.

   • Consumes all prey in its chamber, then spins a cocoon.

6. Overwintering:

   • Pupates inside the burrow and remains dormant over winter.

   • Emerges as an adult the following summer to repeat the cycle.

Best Native Host Plants to Support Sphex pensylvanicus (Chicago Region)

The Great Black Wasp needs nectar-rich mid-to-late summer blooms for adult feeding, plus loose, sunny soil for nesting.

Nectar Sources

(All native to the Chicago area; bloom July–September)

• Pycnanthemum virginianum (Virginia Mountain Mint) – highly attractive to wasps

• Pycnanthemum tenuifolium (Narrow-leaved Mountain Mint)

• Eutrochium purpureum (Sweet Joe-Pye Weed)

• Eutrochium maculatum (Spotted Joe-Pye Weed)

• Monarda fistulosa (Wild Bergamot)

• Asclepias tuberosa (Butterfly Weed)

• Solidago spp. (Goldenrods, especially S. speciosa, S. rigida, S. juncea)

• Rudbeckia hirta (Black-eyed Susan)

• Vernonia fasciculata (Ironweed)

Habitat Support

• Nesting substrate: Areas of bare or sparsely vegetated sandy or loose loam soil in full sun are essential for nesting. Avoid heavy mulch or dense turf in these patches.

• Avoid pesticides: Even “bee-safe” sprays can harm hunting adults or developing larvae.

Key Notes for Chicago

• Activity period: Mid-July through late August is peak visibility.

• Often seen nectaring in prairie restorations, park gardens,

Sphex pensylvanicus – the great black wasp – is a large, solitary, thread-waisted wasp native across most of North America, including the Chicago region. Adults are up to 1.5 inches long, a glossy black with a blue-iridescent sheen, and are powerful fliers.

Ecological role

• Predator: Females hunt katydids, grasshoppers, and other orthopterans, sting to paralyze them, and drag them to their burrows. This helps control herbivorous insects that can damage vegetation.

• Pollinator: Adults feed on nectar from a wide variety of summer-blooming plants, moving pollen between flowers as they forage.

• Food web link: They themselves are preyed upon by birds, spiders, and other predators.

Lifecycle

1. Emergence – Adults appear mid- to late summer (July–August in Chicago).

2. Mating – Males patrol sunny areas and intercept females.

3. Nesting – Solitary females dig burrows in bare, sandy or loose soil in sunny, open spots. Each burrow has several side chambers.

4. Provisioning – Females capture and paralyze multiple katydids/grasshoppers per cell, lay an egg, and seal the chamber.

5. Larval stage – Egg hatches in a few days; larva feeds on still-living prey, then spins a cocoon.

6. Overwintering – Larvae pupate underground and overwinter, emerging as adults the following summer.

Supporting Sphex pensylvanicus in Chicago

• Provide nectar sources during their active period (July–September). Good native plants include:

  • Pycnanthemum virginianum (Virginia mountain mint)

  • Pycnanthemum tenuifolium (Narrow-leaf mountain mint)

  • Eutrochium purpureum and E. maculatum (Joe-Pye weeds)

  • Monarda fistulosa (Wild bergamot)

  • Asclepias tuberosa (Butterfly milkweed)

  • Solidago rigida, S. speciosa, S. juncea (Goldenrods)

  • Vernonia fasciculata (Ironweed)

  • Rudbeckia hirta (Black-eyed Susan)

• Maintain small patches of bare, loose, sunny soil for nesting; avoid mulching every inch of ground.

• Eliminate or reduce pesticide use, especially broad-spectrum insecticides, which can harm both adults and prey populations.

With nectar plants for the adults, hunting habitat for prey, and nesting substrate, this striking wasp can thrive in Chicago gardens and serve as both a pollinator and a natural pest controller.