Wednesday, January 16, 2013

Wasp Wednesday: Great Black Wasp

Few North American wasps are as conspicuous as the Great Black Wasp, Sphex pensylvanicus. This all-black insect with violet reflections on its wings is so large as to sometimes be mistaken for a tarantula hawk wasp. Males average 22 millimeters in body length, while females are about 28 millimeters (up to 35 mm) and more robust.

This is also a common and widespread species, ranging from southeast Canada to northern Mexico, and as far west as southern California. It is absent from the Pacific Northwest, and while I lived in Arizona for a decade, I did not encounter this species there, either. It is perhaps most abundant along forest edges in deciduous woodlands, sumac thickets, gardens, and fields with scattered trees.

Habitat preference is governed by the need for the adult wasps to find flower nectar to fuel their flight; and for females to find katydid prey. Milkweed (Asclepias spp.), thoroughworts (Eupatorium spp.), mountain mint (Pycnanthemum spp.), buttonbush (Cephalanthus occidentalis), camphorweed (Pluchea spp.), Rattlesnake Master (Eryngium yuccifolium), White Sweet Clover (Melilotus alba), and goldenrod (Solidago spp.) are among this wasp’s favorite rest stops. Females dig burrows in soft soil, usually in sheltered spots such as the dirt floors of abandoned barns or other outbuildings.

Though they are solitary, several females may nest in close proximity to one other. Each burrow is an angled tunnel about an inch in diameter and over one foot long. At the end of the burrow is a chamber from which other cells are added over time. The female leaves the nest entrance open while she goes about finding katydids. Her prey can be enormous. Adult Greater Angle-wing Katydids (Microcentrum rhombifolium) can be 52-63 millimeters long and are quite heavy. The Lesser Angle-wing Katydid (M. retinerve) is another prey species, as is Scudderia furcata, the Fork-tailed Bush Katydid. An average of three paralyzed katydids goes into each cell in the nest, a single egg being laid on the first of those victims.


Greater Angle-wing Katydid female

The wasp larva that hatches from the egg feeds and grows for about ten days, eventually reaching a length of 30-35 millimeters, and a diameter of 7-10 millimeters. Larval insects are almost always larger than the adult stage because so much energy is spent in the pupal stage. The larva probably passes the winter in a pre-pupal state, pupating the following spring and then emerging in summer.

Female Great Black Wasps are incredibly successful at finding katydids. One field researcher, Reverend John A. Frisch of Woodstock College in Maryland plugged the nest entrances in one aggregation. The result was 252 katydids piled up in only five days. That worked out to an average of nearly 17 katydids per wasp per day (Evans, 1963). The wasps fly with that heavy load, too.

Hauling a large, heavy katydid back to the nest can attract unwanted attention, and one entomologist in Rhode Island observed House Sparrows (Passer domesticus) and, to a lesser degree, Gray Catbirds (Dumetella carolinensis) intercepting female wasps and relieving them of their paralyzed prey. As many as one-third of return trips by all the female wasps observed ended this way: empty-handed (Benntinen & Preisser, 2009).

The adult wasps themselves can be parasitized by Paraxenos westwoodi, one of the insects called stylopids or “twisted-wing parasites.” Wasps that have deformities of the abdominal segments, often with a bullet-like capsule or two protruding between segments, are victims of stylopids.

An interesting piece of historical trivia is that this species was the first insect subject of a paper by a naturalist native to North America. Observations of the Great Black Wasp by John Bartram (Philadelphia) were presented to the Royal Society (Royal Society of London for Improving Natural Knowledge) by Peter Collinson in 1749. The species was not officially described until 1763 by Carl Linnaeus.

Sources: Benntinen, Justin and Evan Preisser. 2009. “Avian kleptoparasitism of the digger wasp Sphex pensylvanicus,” Can. Ent. 141(6): 604-608.
Evans, Howard E. 1963. Wasp Farm. Ithaca, NY: Comstock Publishing Associates (Cornell University Press). 178 pp.

17 comments:

  1. Nice post Eric! I've grown fond of these wasps since the summer, when I was finding many of them. They seem to like hanging around Japanese knotweed (Fallopia japonica)flowers as well.

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    1. Thank you for the compliment! Yes, I forgot about Japanese Knotweed, perhaps optimistically so :-)

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  2. They particularly love my mountain mint. Will they sting humans?

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    1. Hi, Diane! The females are certainly capable of stinging, but you have to literally molest one to get it feeling threatened enough to deploy its stinger. Plus, males (which are anatomically incapable of stinging) are far more common at flowers in my experience. Females are busy digging nests and hunting katydids.

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  3. I had to post a comment because I just discovered these wasps in my garden today; I'd never seen them before. I live in the Pacific Northwest (Medford, OR)- was surprised to read that they are supposed to be absent here. One of these beauties was enormous - about the length of my little finger - and I saw 2 others that were a bit smaller. I had to find out what kind of wasp they are and my search led me here. Great informative post! I am a first year beekeeper and am frequently out observing them, and the bumble bees, in the yard, that's how I discovered the Great Black Wasps. How exciting that they are here!

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    1. Stephanie: You may have a different wasp altogether. I'd love to see an image of what you are talking about, and learn what kind of prey it is bringing in. I'm thinking it is a species of Palmodes, or even Prionyx, rather than the subject of this blog post. I lived in Oregon the first 27 years of my life and never saw a Great Black Wasp there, either.

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  4. Eric I have these wasps under the deck of my front door, they have never bitten anyone and my family has learned to just walk by them or ignore them but when people come to the front door it is pretty scary to be swarmed by these big black wasps. Every year we seem to get more and more and they love the Minnesota sun in July. Any ideas on how to get them to move on or move out? NancyB

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    1. I'm sorry, Nancy, but my business is not to suggest "pest control" for what are essentially harmless insects. Unless you physically grab a female wasp, you are not going to get stung. Period. The wasps use landmarks to locate their nests, and are circling the guests at your door because they interpret the people as new landmarks (or the wasps are simply disoriented by the sudden appearance of a person).

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    2. Hello Eric, as with nancy I have seen a wasp that looks a lot like this one, as far as if it is or is not I will give you what I can. I may be able to find the body of the wasp. We can't take risks, allergies. But I noticed it when it flew into a small hole in the inside of my hose reel for storring the garden hose. It was carrying a long piece of dryed grass. This wasp was much larger than the normal wasps I get . I would guess about 2/3ds larger.

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    3. Fred, what you are describing is a "grass-carrier" wasp, same family as the Great Black Wasp, but different genus and different nesting behavior. Here's one of my blog posts about them: http://bugeric.blogspot.com/2011/02/wasp-wednesday-more-on-isodontia.html

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  5. If these wasps are not in the Pacific Northwesr why do you suppose I found one in my garden, in the Bamboo with an ant on it's stinger? I live on the pennisula in NW Washington state.

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    1. Hi, Debra: I imagine you probably found a different kind of wasp altogether. In my response to Stephanie Gentry above, I suggested she might have seen a Palmodes wasp instead....Ants will antagonize wasps that visit aphid colonies they are guarding. The ants will also scavenge dead insects, even very large ones.

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  6. Hi Eric - I live in Bellevue (suburb of Omaha, I see you're coming to visit the zoo - it is AWESOME, so enjoy yourself), and this afternoon one of these wasps must have gotten trapped in my garage and buzzed in past me into the basement. Not knowing if it was going to sting me, I've pretty much left it alone. The lights are out down there now so no idea where it is. I will be using the treadmill down there in the morning (it is too hot and humid to run outside) and I'm wondering if this wasp will be trying to find it's way outside. I'd love to help it, but it's a bug.... and it could hurt me or the dogs.... suggestions that will save us all a little hurt? :-) Thanks!

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    1. Hi, Kelley! Most insects trapped indoors fly to light, so if you have a window or windows in your basement, it will fly to those. Then just put a glass or other transparent container over the insect and slip a card between bug and the window, trapping the insect inside the container. Then you can release it outdoors. That said, this species is in no danger of going extinct, so if you must kill it, then don't feel *too* guilty.

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  7. Greetings! I found one of these lovely, iridescent blue-black babies hanging around on the white goosefoot (Chenopodium Album) outside my back door (Milan, MI). It was terrifying my children (ages 5 and 3) so they wouldn't use the door. I looked it up and happened upon your page! Thanks for the great information! We're all pleased to learn it won't sting us, but big, black flying things are scary nonetheless!

    I'm going to try removing the plant it seems to favor (there's a bunch elsewhere in the yard) to see if the wasp hangs out around the door less. I'm sure her nest is somewhere in the crumbling cinderblock wall of our small porch right there, so she probably won't go TOO far, but if we can get in and out of the door without a two-inch wasp in our faces, that'd be lovely. :)

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  8. Just discovered these burrowing under my house in Upstate South Carolina. Any reason to be concerned ?

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    1. Hi, June. No reason for concern. Just don't disturb them for the week, more or less, that they need to nest. You wouldn't likely get stung anyway, but locations suitable for nesting are sometimes hard to come by for solitary wasps and bees.

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