The Wasp Wall

South Cape May Meadows in Cape May, New Jersey is a property managed by The Nature Conservancy (TNC) for birds and other wildlife. Near the parking lot stands a shed that itself is something of a refuge for a whole community of insects. One wall, facing west and with beams that make something of an overhang or trellis, is being worked over by the Eastern Carpenter Bee, Xylocopa virginica. The abandoned nests of these solitary bees are then used by mason wasps, leafcutter bees, and other solitary Hymenoptera.

The shed at South Cape May Meadows, behind the arbor entrance

During our visit this past September 24, we noticed the holes, then soon saw females of the Four-toothed Mason Wasp, Monobia quadridens, exploring some of those cavities. I wrote about this species previously, detailing its life cycle, but this was the first time I had observed them coming and going from nests.

Female Monobia quadridens entering her nest

One female delivered a paralyzed caterpillar during our observations. It was a surprisingly small larva given the size of the wasp, but then she caches several victims in each cell before laying a single egg, putting up a partition of mud, and then starting a new cell along the length of the tunnel inside the wood.

Female cuckoo wasp, Chrysis sp., prospecting for a host

One might think that nests in such solid material would be impermeable to parasites, but not so. We watched a brilliant blue-green cuckoo wasp, Chrysis sp., investigate some of the holes for occupants. Given a nest in progress, she would infiltrate and lay her own egg inside. Her larva would then consume the prey items left by the rightful owner for its offspring. Cuckoo wasps are nearly impregnable, with a very dense exoskeleton that deflects the bites and stings of host wasps. Cuckoo wasps can roll into a ball to further protect themselves.

Female Leucospis affinis ovipositing in a host nest

A less common parasitic wasp also came to the wall. Leucospis affinis is a large chalcidoid wasp. The female is easily recognized by the whip-like ovipositor that curls over the top of her abdomen. The ovipositor is the organ she uses to lay her eggs....by drilling through the solid wood directly into one of the cells of her host. How she divines the location of a host larva through a layer of dense cellulose is a mystery to me, but her aim is usually true.

Nest closure of mason wasp or carpenter bee

A completed nest of a mason wasp is usually identified by the mud plug that closes the entrance to the hole in the wall. Because the soil at Cape May is essentially all sand, it was difficult to tell if we were looking at a sand closure or a sawdust closure that would be the work of one of the carpenter bees.

Nest closure of leafcutter bee, Megachile sp.

Easier to identify was the completed nest of a leafcutter bee, genus Megachile. Leafcutter bees snip oval pieces from leaves of living plants and fashion those clippings into barrel-shaped cells that they stack along the length of a tunnel in wood, or underground in the case of a few species. The female bee then cuts at least one perfectly circular leaf fragment that serves as a "lid" for the completed cell.

Nest of grass-carrier wasp, Isodontia sp.

We found one hole filled loosely with bits of grass, and we surmise this was the work of yet another kind of wasp, the grass-carrier. These solitary wasps, related to mud daubers in the family Sphecidae, use dry grass to fill, and/or partition, and plug their nest tunnels. Near Cape May Point State Park we did witness a female Isodontia mexicana select and bite off a dry grass stem to take back to her nest, so we know these insects were active.

Female grass-carrier wasp, Isodontia mexicana, cutting a piece of grass

Ironically, one other kind of wasp was tearing the wall down one mouthful at a time. Workers of the Bald-faced Hornet, Dolichovespula maculata, would alight on the wall and begin chewing off wood fibers to mix with their own saliva. This creates a pulp that they use to make durable paper nests. Looking more closely at the wall we realized that the scores of yellow streaks on the otherwise weathered gray wooden surface were where yellowjackets (of which the Bald-faced "Hornet" is just another species) had stripped fibers for use in building their nests.

Bald-faced Hornet gathering wood fibers to make paper

No doubt, earlier in the season there would be even more activity around this wall. The shed is still standing, sturdy as ever, so the insects are not doing much, if any, structural damage. Please consider that if you find that your own shed is becoming home to carpenter bees and other insects. You may find yourself as enthralled as we were by the little ecosystem started by carpenter bees.

Female Monobia quadridens exiting her nest

Sources: Evans, Howard E. 1963. Wasp Farm. Ithaca, NY: Comstock Publishing Associates (Cornell University Press). 178 pp.
Buck, Matthias, Stephen A. Marshall, and David K.B. Cheung. 2008. “Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region,” Canadian Journal of Arthropod Identification No. 5: 492 pp. (PDF version).
Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.
Krombein, Karl V., et al. 1979. Catalog of Hymenoptera in America North of Mexico Vol.2 Apocrita (Aculeata). Washington, DC: Smithsonian Institution Press. Pp. 1199-2209.

Wasp Wednesday: More on Isodontia

Last week I showed a short video introducing you to a puzzling phenomenon in suburban areas of eastern North America. A quick review: Some homeowners in the U.S. and Canada, upon sliding open their windows, have been startled to discover the tracks filled with dry grass, dead insects, and live “worms.” Even the odd wasp has flown out. What is going on here?

Certain solitary wasps called “grass-carriers,” genus Isodontia, seem to have found window tracks make ideal nesting sites. Each female wasp makes her own nest, usually a series of cells along the length of the tunnel (though one species forms a communal brood chamber much like a bird nest).

After selecting a site, she goes in search of tree crickets or small katydids which she paralyzes with her sting and carts back to the nest. Once a cell is filled with victims, she lays an egg, and makes a partition of dry grass. Then she begins the provisioning process again, until the tunnel is filled with cells. She finishes the nest by plugging the entrance with dry grass, such that it looks as if someone has shoved a tiny broom into the hole, handle-first. Her job complete, she leaves permanently.

The larva that hatches from each egg grows by consuming the fresh prey insects. These are the “worms” that people find in the window tracks. After finishing its meals, the larva then enters the pupal stage, and an adult wasp emerges later (the following summer in northern climates).

Grass-carriers are not pests, and not aggressive towards people or pets. You will not get stung unless you physically grab a female. Males have no stinger at all.

My initial theory was that the wasps much prefer using natural cavities in dead wood, but few such natural resources exist in suburban settings. My revised theory is that the wasps may find window tracks to be a superior nesting site. Perhaps the space is “roomier” than conventional natural cavities. Maybe the parasitic flies and wasps that plague Isodontia have not yet caught on to the new nesting strategy, therefore giving Isodontia an advantage that yields more success in terms of offspring reared to maturity.

Please tolerate these wasps if you can, they are fascinating to watch. Otherwise, simply flushing the wasp and cleaning the track should discourage her from trying again.

Meanwhile, look for the adult wasps on wildflowers, especially sweetclover, sumac, and grape. They will also frequent aphid colonies, lapping up the “honeydew” secreted by the sap-sucking pests. Notice that these wasps usually have the wings splayed at rest, in contrast to other sphecid wasps that habitually fold their wings flat over their abdomen while sipping nectar.

The species shown in the images accompanying this article is Isodontia mexicana, very common over most of the eastern U.S. There are also five other species occurring in North America.

Wasp Wednesday: Audition Video

I had the privilege of auditioning for a pool of new talent with the BBC Natural History Unit back in December of 2008. They wanted a demo DVD, so I had to enlist some help. I decided I would use grass-carrier wasps of the genus Isodontia, family Sphecidae, as my subject. The result is shown below.

A huge amount of thanks goes to Kirk Sellinger of Kalypsis Productions. Kirk helped me out on a moment's notice, charged reasonable rates, and shared a few tricks of the production trade. When he isn't working with minor clients like me, Kirk joins National Geographic tours documenting both the natural history and the guests, making DVDs available to the guests at the end of the expedition.

Nothing became of this particular audition for the BBC, but they were most gracious. I would very much like to make a living interpreting insect and spider natural history through all types of media, regardless of whether I am in front of the camera or not. Watching myself in this video I might actually prefer to be behind the scenes. I welcome inquiries from those who produce nature documentaries, or referrals to production companies and others in that business.

I have appeared on television before, locally (at the "Bug Fest" at the Arkansas Museum of Discovery in Little Rock, July, 2000) nationally (a guest on Donahue in February, 1989 for a discussion on children of divorce), and syndicated (Make Peace With Nature in the 1990s). I have also performed stand-up comedy for a live audience at the end of a comedy workshop.

Since I will be out of my current part-time job come May of this year, I figure I better get started on my next move. Creative enterprises really are "my thing," and I look forward to collaborating with like minds. Oh, and I’ll be back next week with a bit more on Isodontia. Thanks.