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Autumn and the Last Wasps

Maybe it was the full moon. Maybe it was something in the air—the mild air of a mild autumn day—but with a hint of change; a leaf flutter or a minute drop in barometric pressure, some early message from a storm, and not a big storm, fifteen hundred miles away, far out over the Pacific Ocean and still two days from landfall.

First the deer came bounding by—all of our usual crowd: the two does and their three fawns. My office/studio is in the barn—a nicely windowed corner where I can watch the meadow, the knoll, and the animal-maintained trail along the creek. To say that the deer bounded by understates it: they came at a gallop. And prancing behind: a large well-racked buck, evidently with one thing on his mind, which turned out to be the alpha female, the mother of the twins.

The cat was in the window box when the deer ran through and she sat bolt upright wide-eyed. She’s always been a deer watcher, but I don’t think she’d ever seen this. The doe ran back and forth across the meadow, the buck pursuing her without ever breaking his stride. The twins thought the whole chase was a great game, and bounded and pranced after the two adults. They all crossed the stream, crossed back, and finally disappeared over the knoll.

Next two foxes appeared—with gray bushy tails and gray backs but with the russet-brown clearly flashing from under their flanks—chasing each other in circles, feinting and leaping into the air. We’d already had two heavy rainstorms in October, so the meadow was green.

Next Laura called from the house and said that the bedroom screen had been left open and that a lot of wasps were in the room. It turned out she wasn’t exaggerating. The wasps had taken up position on the windows and on the wall in several large clusters—”aggregates”—the wasps all piled together beside and on top of each other in tight groups.

It turns out that “aggregating” is a common behavior for paper wasps in the fall and winter. As the weather cools, the late-hatched females—better fed and with more fat reserves than their older sisters—seek shelter to huddle together for the winter. These are the females who, if they survive (and not all of them do), will begin new nests in the spring. The aggregates we were seeing were “pre-hibernation” aggragates. As winter sets in more seriously the wasps move to a more sheltered spot called a “hibernaculum,” under the bark of a down tree or in the crevice iof a rock, or, of course, in an attic.

Several recent studies have appeared on the social behavior of paper wasps. One, in Science, purported to prove that female wasps who helped to feed a nest to which they were not related were not behaving altruistically, since they stood a chance to inherit the nest. As the wasps were, after all, acting according to “plain old self-interest,” and not from altruism, the scientific model was able to dodge what is evidently a most challenging and perplexing problem.

Another study found that on warm winter days a wasp will occasionally disengage herself from the group to foray for food, and will indeed share the food with the other wasps, even though they are not her sisters (nest mates) or even of her species or genus.

a groggy wasp: Mischocyttarus flavitarsisWhen I call these wasps “paper wasps” I do not mean hornets, the genus Vespa, who also make paper nests, but with a covering. I refer to those wasps building open comb nests, usually under eaves. Because the nests are open and the wasps are rather tolerant, the social behavior of these wasps has been studied much more than that of hornets or yellowjackets (genus Vespula). The commonest species of paper wasp and the one most studied is Polistes. I had always assumed that the sometimes huge open nests ringing the roof of my barn were Polistes, but I had never checked. Fortunately, a key was available online: “The Social Wasps of California,” by R. M. Bohart and R. C. Bechtel, Bulletin of the California Insect Survey Volume 4, No. 3, University of California Press 1957. I didn’t want to kill the wasps, so I caught one in a jar and put it in the refrigerator for fifteen minutes, after which it was easy to handle.

Now insect keys, while structured like a botanical key, take some getting used to. It’s all about “parts,” meaning body parts like tarsal claws, the clypeus, the gaster, the hind tibia and basitarsus, the seventh tergite, and a score of other specialized terms that I had never heard of. Fortunately, these authors provided some drawings. But still: examining the flowering parts of a plant is not the same as inspecting the ventral edge of the aedeagus (the male sexual organ of an insect). But it turned out to be easy:

1.    –Second gastral segment not swelling abruptly at or near base in dorsal view    ->2
–Second gastral segment swelling abruptly at or near base in dorsal view    ->4

The drawing showed that the gastral segments were the same as what I had always called the abdomen, and that they were counting from front to back. In my wasp, the first gastral segment was narrowed and elongated, not so much as a mud dauber, but enough so that the second gastral segment was clearly abruptly widened. That took me to (4).

4.    –First abdominal tergite broader than long    ->Brachhygastra
–First abdominal tergite much longer than broad    ->5

Again, the drawings helped immensely, and I didn’t have to find out just what the difference was between a gaster segment and an abdominal tergite—whatever it was, it was much longer than broad. Which took me to (5).

5.    –Claws of tarsi simple    ->Mischocyttarus
–Claws of tarsi toothed beneath or bifid near apex    ->Zetbus

Again, it was easy: the delicate feet of the wasp ended in a simple, untoothed claw. I had Mischocyttarus Saussure, which means something like “pediceled nest.” The genus is mainly South American, and the sometimes extended stem from which the nest hangs is thought to be a protection against ants. In our species the pedicel is short and looks just like that of many Polistes species.

There wasn’t any species key because only one occurs in California: Mischocyttarus flavitarsis (used to be Polybia flavitarsis). The authors notes stated that M. flavitarsis builds similar nests to Polistes, “but with fewer cells.” Since some of the nests contain well over two hundred cells, Polistes nests must get very large indeed. They also stated that M. flavitarsis females hibernate together with two Polistes specis. My groggy female was starting to move, so I took her out into the sun. She sat a moment, and was gone.

After deciding how I was going to pronounce the name (/’mis ko si ‘tar us/), I found out that the “western paper wasp” or the “yellow-legged paper wasp” has an even more fluid social structure than Polistes. That is, the nest foundress, what we might better call an alpha female than a queen, sometimes chucks it to go be a worker at another nest. Wasps performing as workers seem to change jobs when they feel like it: sometimes foraging, sometimes nursing the larvae. Even the males occasionally work. All of them spend a lot of time just hanging out and preening themselves. Besides pyrethrin and parasitic wasps and flies (which are a constant problem), the main enemy of the wasps, at least where I live, is the blue jay. I’ve seen blue jays knock down the nests, wait for the wasps to abandon it, and then feed on the larvae at leisure.

Wasps are good to have around a house. Mud daubers prey wholly on spiders—one species exclusively on black widows—that’s why they are hovering around eaves and crevices. Paper wasps will sting you if you bug them too much, or mess with their nest, but for the most part you almost have to sit on them to get stung. And if you live in a “permeable” cabin and let the wasps stay inside all winter, when they are groggy and crawling instead of flying, sooner or later that will happen. Kind of wakes you up.

Further Reading:
Field entomologists, beginning with Henri Fabre, tend to be colorful writers, and their books age well. Maybe that’s because the writers spend so much time lying flat in the dirt waiting for a wasp to emerge from its tunnel. My favorite wasp book is The Ways of a Mud Dauber, by George D. Shafer (Stanford University Press, 1949). One can get a clue of what is to come from the dedication: “To “Crumple-Wing,” who was true to the tradition of all mud daubers. She honored her Creator and published His name so that ‘He who runs may read.'”

Shafer describes his investigations of the digestive and execratory systems of Sceliphron cementarium, but the heart of the book is his story of his personal relationships with two of the mud daubers. Shafer often felt that the wasps were as curious about him as he was of them. He “tamed” one wasp—one who seemed less shy than most–by repeatedly offering her a bit of honey on his finger tip. Finally, after some days, she decided to accept it and hopped onto his finger and ate the honey. After that she would fly up to him often, landing on his hand or finger, even if she wasn’t interested in eating. “After five or six weeks she began to show some evidence of friendship.”

One day Shafer was working in his lab with an alcohol lamp. The door was ajar and his familiar wasp flew in and hovered around his hands. Fearing that the wasp might singe her wings in the flame, he caught her with his handkerchief and put her out. As he describes it, after such an indignity (and from a friend!), the wasp spurned him for four days. I’ll leave the story of Crumple-Wing for the book.

Another good wasp read is Wasp Farm, by Howard Ensign Evans (Natural History Press, 1963). Most of Evans’s engaging stories are about sand and digger wasps, but there are also chapters on social wasps. It’s a charming read. Evans also co-authored a somewhat more technical book, The Wasps, with Mary Jane West Eberhard.

There are a couple of new-ish  books (one reviewer said “even though this book is already ten years old . . .”) that look interesting: Evolution of Social Wasps, by James Hunt, and The Social Biology of Wasps, a collection of scientific essays edited by Kenneth Ross and Robert Matthews. I’ll report on those later.


  1. Mike Riter writes:

    Love your wasp article! I never saw “pre-hibernation aggregating” mentioned before. Where I live, in Columbia County, just south of Albany in New York, it’s common for the wasps, Pachysomoides fulvus and Polistes dominula to hibernaculum in the nests of Dolichovespula maculata. Do you think P. fulvis has a meal on the larvae before hibernation?

    August 29th, 2013 at 10:26 am

  2. Mike Riter writes:

    I’m thinking, since you say wasps will sometimes look for food on warm winter days, maybe the coolness of winter keeps the larvae inside the D. maculata nests fresh enough to snack on during such days??
    I collect D. maculata nests, in case you’re wondering how I know these wasps hiberaculum inside them.
    I was given a nest in a black paper bag in November and forgot about it until May. When I opened it there were @ 30 live P. fulvus.

    August 29th, 2013 at 10:45 am

  3. susanna writes:

    Great post! May I ask how you got the aggregating wasps out of the room? I currently have a few groups in my living room after I inadvertently knocked their nest down from my chimney when I opened & closed the flue. Thanks!

    October 7th, 2013 at 2:31 pm

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