Meeting the Great Black Wasp

My computer’s dictionary defines “insectary” as “a place where insects are kept, exhibited, and studied.”  This definition conjures up images of a dusty museum room filled with glass-topped cases of brittle specimens, each with a pin inserted through its thorax.  A thin rectangular slip of paper just below the head of the pin provides the scientific name of the creature, perhaps also where it was found, and when.  I’ve never felt very comfortable, certainly not inspired, by such a place.  Too much taxonomy for its own sake.

The garden, or a section of the garden, can be another kind of insectary, a collection of flowering plants chosen for their potential to attract pollinators, predatory insects that feed on herbivores, and the herbivores as well.  This is a place worth visiting on a regular basis.

On a warm summer day you can move quietly among the garden’s plants, observing the interactions of flowers and insects, pursuing those observations to a deeper understanding of connections between plants, herbivores, predatory insects, birds, and you, the gardener.  I recall such a day, an August afternoon, standing in the center of a patch of swamp milkweed, the day I first met the Giant Black Wasp.

I was visiting a coastal Maine residential landscape filled with regionally native plants, a garden close enough to home to provide visual ownership of plants that we do not grow in our own garden.  On one edge was a rain garden planted with native herbaceous species that love wet feet, including swamp milkweed, Asclepias incarnata.

Swamp milkweed grows wild in swamps and wet meadows, but it is surprisingly tolerant of average well-drained garden soil.  I have seen it colonize a vacant lot of compacted soil surrounded by asphalt and concrete.  Blooming in July and August, it has an erect, clump-forming habit, reaching three to four feet tall with a deep taproot.  Tight clusters of hourglass flowers, wide at the bottom and top but constricted in the middle, range in color from pink to mauve, almost red in some locations.  These are followed by 4-inch-long seed pods which split open at maturity to release silky-haired seeds to the wind.

I stood in the midst of the blooming milkweeds, astonished by the diversity of insects swarming and crawling among the flowers and along the stems.  On some plants, the earliest flower clusters had produced bunches of immature green seed pods, the stems of which were crowded with orange aphids that I later determined to be oleander aphids, Aphis nerii, a common herbivore associated with milkweeds worldwide.

I looked up from photographing the aphids and there, inches from my nose, was a Giant Black Wasp crawling purposefully across a cluster of milkweed blossoms.  At least 1-1/2 inches long, she was both beautiful and threatening, black except for wings that reflected a shining metallic blue in sunlight.  (The wasp’s sex was determined later in the day when a field guide showed the male to be much smaller.)

She ignored me and the myriad other insects swarming around her, completely focused on foraging for nectar while moving pollen from flower to flower.  After a few moments of feeling intimidated by the size of her stinger, I followed her from one flower cluster to another with the camera.

Later that day I sat down with field guides to learn as much as I could about the wasp named Sphex pennsylvanicus.  Also known as Katydid Hunter and the Steel-blue Cricket

A female Great Black Wasp forages for nectar on a cluster of swamp milkweed blossoms.

Hunter, she belongs to a group of solitary hunting wasps collectively called digger wasps, a reference to the construction of their nesting tunnels in soft soil.

It is the male wasp’s responsibility to pick the nest site and keep competitors away while choosing a mate.  The female is the digger, using her heavy-duty mandibles to loosen the soil.  Using her legs as a rake, she compacts a lump of soil, holds it in place under her chin with her front pair of legs, and transports it to the surface where she deposits it in a pile.  Her nesting tunnel is long, with multiple egg chambers.  While not social insects, several females may excavate nesting tunnels in the same area.

After constructing the nesting tunnels, but prior to laying eggs, the female provisions each egg chamber with food for the developing larva.  Katydids and grasshoppers, often much larger than her, are her primary prey.  She first provisions each chamber with one insect which she has captured and paralyzed with three stings before gluing an egg to its underside.  Although immobile, the prey will live until the egg hatches and the larva begins to feed.

During its development, the larva will consume between two and six katydids or grasshoppers, so the adult female spends a good portion of her time provisioning each chamber of her nest.  (Forget the male at this point, he’s just the sperm donor.)  When a chamber is fully provisioned, she fills it, pushing in soil and tamping it down either with her head alone or with the aid of a small leaf or pebble, placing the “tool” on the loose earth and pressing her head against it while vibrating her abdomen.  After the egg hatches, the larva spends about 10 days feeding and then pupates through the winter.

Provisioning each nest chamber with sufficient food takes up much of the female’s time and the task is made even more arduous when a captured and paralyzed prey never makes it to the nest.  The female wasp can become a victim of kleptoparasitism (parasitism by theft) by house sparrows and gray catbirds as she drags her prey back to the nest.  Researchers at University of Rhode Island determined that as many as one third of a wasp’s provisioning attempts are thwarted by avian theft.

As often happens, a few days after my first encounter with a Great Black Wasp, I met another female foraging on a Queen Anne’s lace in our garden insectary.  Paying me no heed, she moved deliberately across the cluster of tiny flowers, filling up on nectar.  I smiled at the thought that somewhere in the garden, perhaps along the back edge of a bed where the soil had been softened by digging, there was a nesting tunnel where well-fed pupae would spend the winter.

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About Reeser Manley

I was born in Laramie Wyoming but moved to the southeast at an early age. I was educated through my B.S. in Biology in the Columbus, Georgia area, then crossed the Chattahoochee River to earn my M.S. in Botany at Auburn University. For the next ten years, I worked as Horticultural Manager for the George W. Park Seed Co. in Greenwood, S.C. At 40 years of age, I decided to return to graduate school and in 1994, I earned a Ph.D. in Horticultural Science from Washington State University, Pullman, Washington. Fast forward through 10 years at university (7 at UMaine, Orono) and you find me teaching high school science in Eastport, Maine, the edge of the world, and writing a weekly garden column for the Bangor Daily News. My new book, The New England Gardener's Year, a Month-by-Month Guide for Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, and Upstate New York”, will be published later this year by Cadent Publishing. You can learn more about the book by visiting its Facebook page: http://www.facebook.com/pages/The-New-England-Gardeners-Year/187285218055676.)